This work was supported by JSPS KAKENHI Grant Numbers JP24750023, JP24350012, MEXT KAKENHI Grant Numbers JP26104534, JP16H00850, JP26102541, JP16H00782, and MEXT-Supported Program for the Strategic Research Foundation at Private Universities, 2015&#8211;2019.

<ol><li>Polívka, T., Herek, J. L., Zigmantas, D., Åkerlund, H. -E., Sundström, V. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Direct+Observation+of+the+%28Forbidden%29+S1+State+in+Carotenoids%5BTitle%5D)+AND+%22Proceedings+of+the+National+Academy+of+Sciences+of+the+United+States+of+America%22%5BJournal%5D)">Direct Observation of the (Forbidden) S1 State in Carotenoids.</a> Proceedings of the National Academy of Sciences of the United States of America. 96 (9), 4914-4917 (1999).</li>
<li>Takaya, T., Iwata, K. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Relaxation+Mechanism+of+%CE%B2-Carotene+from+S2+%281Bu%2B%29+State+to+S1+%282Ag-%29+State%3A+Femtosecond+Time-Resolved+Near-IR+Absorption+and+Stimulated+Resonance+Raman+Studies+in+900-1550+nm+Region%5BTitle%5D)+AND+%22Journal+of+Physical+Chemistry+A%22%5BJournal%5D)">Relaxation Mechanism of β-Carotene from S2 (1Bu+) State to S1 (2Ag-) State: Femtosecond Time-Resolved Near-IR Absorption and Stimulated Resonance Raman Studies in 900-1550 nm Region.</a> Journal of Physical Chemistry A. 118 (23), 4071-4078 (2014).</li>
<li>Takaya, T., Anan, M., Iwata, K. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Vibrational+Relaxation+Dynamics+of+%CE%B2-Carotene+and+Its+Derivatives+with+Substituents+on+Terminal+Rings+in+Electronically+Excited+States+as+Studied+by+Femtosecond+Time-Resolved+Stimulated+Raman+Spectroscopy+in+the+Near-IR+Region%5BTitle%5D)+AND+%22Physical+Chemistry+Chemical+Physics%22%5BJournal%5D)">Vibrational Relaxation Dynamics of β-Carotene and Its Derivatives with Substituents on Terminal Rings in Electronically Excited States as Studied by Femtosecond Time-Resolved Stimulated Raman Spectroscopy in the Near-IR Region.</a> Physical Chemistry Chemical Physics. 20 (5), 3320-3327 (2017).</li>
<li>Guo, J., Ohkita, H., Benten, H., Ito, S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Near-IR+Femtosecond+Transient+Absorption+Spectroscopy+of+Ultrafast+Polaron+and+Triplet+Exciton+Formation+in+Polythiophene+Films+with+Different+Regioregularities%5BTitle%5D)+AND+%22Journal+of+the+American+Chemical+Society%22%5BJournal%5D)">Near-IR Femtosecond Transient Absorption Spectroscopy of Ultrafast Polaron and Triplet Exciton Formation in Polythiophene Films with Different Regioregularities.</a> Journal of the American Chemical Society. 131 (46), (2009).</li>
<li>Hwang, I. -W., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Carrier+Generation+and+Transport+in+Bulk+Heterojunction+Films+Processed+with+1%2C8-Octanedithiol+as+a+Processing+Additive%5BTitle%5D)+AND+%22Journal+of+Applied+Physics%22%5BJournal%5D)">Carrier Generation and Transport in Bulk Heterojunction Films Processed with 1,8-Octanedithiol as a Processing Additive.</a> Journal of Applied Physics. 104 (3), 033706(2008).</li>
<li>Yonezawa, K., Kamioka, H., Yasuda, T., Han, L., Moritomo, Y. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Fast+Carrier+Formation+from+Acceptor+Exciton+in+Low-Gap+Organic+Photovoltaic%5BTitle%5D)+AND+%22Applied+Physics+Express%22%5BJournal%5D)">Fast Carrier Formation from Acceptor Exciton in Low-Gap Organic Photovoltaic.</a> Applied Physics Express. 5 (4), 042302(2012).</li>
<li>Takaya, T., Enokida, I., Furukawa, Y., Iwata, K. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Direct+Observation+of+Structure+and+Dynamics+of+Photogenerated+Charge+Carriers+in+Poly%283-hexylthiophene%29+Films+by+Femtosecond+Time-Resolved+Near-IR+Inverse+Raman+Spectroscopy%5BTitle%5D)+AND+%22Molecules%22%5BJournal%5D)">Direct Observation of Structure and Dynamics of Photogenerated Charge Carriers in Poly(3-hexylthiophene) Films by Femtosecond Time-Resolved Near-IR Inverse Raman Spectroscopy.</a> Molecules. 24 (3), 431(2019).</li>
<li>Clafton, S. N., Huang, D. M., Massey, W. R., Kee, T. W. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Femtosecond+Dynamics+of+Excitons+and+Hole-Polarons+in+Composite+P3HT%2FPCBM+Nanoparticles%5BTitle%5D)+AND+%22Journal+of+Physical+Chemistry+B%22%5BJournal%5D)">Femtosecond Dynamics of Excitons and Hole-Polarons in Composite P3HT/PCBM Nanoparticles.</a> Journal of Physical Chemistry B. 117 (16), 4626-4633 (2013).</li>
<li>Cook, S., Furube, A., Katoh, R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Analysis+of+the+Excited+States+of+Regioregular+Polythiophene+P3HT%5BTitle%5D)+AND+%22Energy+%26+Environmental+Science%22%5BJournal%5D)">Analysis of the Excited States of Regioregular Polythiophene P3HT.</a> Energy & Environmental Science. 1 (2), 294-299 (2008).</li>
<li>Okino, S., Takaya, T., Iwata, K. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Femtosecond+Time-Resolved+Near-Infrared+Spectroscopy+of+Oligothiophenes+and+Polythiophene%3A+Energy+Location+and+Effective+Conjugation+Length+of+Their+Low-Lying+Excited+States%5BTitle%5D)+AND+%22Chemistry+Letters%22%5BJournal%5D)">Femtosecond Time-Resolved Near-Infrared Spectroscopy of Oligothiophenes and Polythiophene: Energy Location and Effective Conjugation Length of Their Low-Lying Excited States.</a> Chemistry Letters. 44 (8), 1059-1061 (2015).</li>
<li>Takaya, T., Iwata, K. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Development+of+a+Femtosecond+Time-Resolved+Near-IR+Multiplex+Stimulated+Raman+Spectrometer+in+Resonance+with+Transitions+in+the+900-1550+nm+Region%5BTitle%5D)+AND+%22Analyst%22%5BJournal%5D)">Development of a Femtosecond Time-Resolved Near-IR Multiplex Stimulated Raman Spectrometer in Resonance with Transitions in the 900-1550 nm Region.</a> Analyst. 141 (14), 4283-4292 (2016).</li>
<li>Jas, G. S., Wan, C., Johnson, C. K. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Picosecond+Time-Resolved+Fourier+Transform+Raman+Spectroscopy+of+9%2C10-Diphenylanthracene+in+the+Excited+Singlet+State%5BTitle%5D)+AND+%22Applied+Spectroscopy%22%5BJournal%5D)">Picosecond Time-Resolved Fourier Transform Raman Spectroscopy of 9,10-Diphenylanthracene in the Excited Singlet State.</a> Applied Spectroscopy. 49 (5), 645-649 (1995).</li>
<li>Jas, G. S., Wan, C., Kuczera, K., Johnson, C. K. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Picosecond+Time-Resolved+Fourier-Transform+Raman+Spectroscopy+and+Normal-Mode+Analysis+of+the+Ground+State+and+Singlet+Excited+State+of+Anthracene%5BTitle%5D)+AND+%22Journal+of+Physical+Chemistry%22%5BJournal%5D)">Picosecond Time-Resolved Fourier-Transform Raman Spectroscopy and Normal-Mode Analysis of the Ground State and Singlet Excited State of Anthracene.</a> Journal of Physical Chemistry. 100 (29), 11857-11862 (1996).</li>
<li>Sakamoto, A., Okamoto, H., Tasumi, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Observation+of+Picosecond+Transient+Raman+Spectra+by+Asynchronous+Fourier+Transform+Raman+Spectroscopy%5BTitle%5D)+AND+%22Applied+Spectroscopy%22%5BJournal%5D)">Observation of Picosecond Transient Raman Spectra by Asynchronous Fourier Transform Raman Spectroscopy.</a> Applied Spectroscopy. 52 (1), 76-81 (1998).</li>
<li>Sakamoto, A., Matsuno, S., Tasumi, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Construction+of+Picosecond+Time-Resolved+Raman+Spectrometers+with+Near-Infrared+Excitation%5BTitle%5D)+AND+%22Journal+of+Raman+Spectroscopy%22%5BJournal%5D)">Construction of Picosecond Time-Resolved Raman Spectrometers with Near-Infrared Excitation.</a> Journal of Raman Spectroscopy. 37 (1-3), 429-435 (2006).</li>
<li>Sakamoto, A., Matsuno, S., Tasumi, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Picosecond+Near-Infrared+Excited+Transient+Raman+Spectra+of+%CE%B2-Carotene+in+the+Excited+S2+State%3A+Solvent+Effects+on+the+in-Phase+C%3DC+Stretching+Band+and+Vibronic+Coupling%5BTitle%5D)+AND+%22Journal+of+Molecular+Structure%22%5BJournal%5D)">Picosecond Near-Infrared Excited Transient Raman Spectra of β-Carotene in the Excited S2 State: Solvent Effects on the in-Phase C=C Stretching Band and Vibronic Coupling.</a> Journal of Molecular Structure. 976 (1-3), 310-313 (2010).</li>
<li>Yoshizawa, M., Kurosawa, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Femtosecond+Time-Resolved+Raman+Spectroscopy+Using+Stimulated+Raman+Scattering%5BTitle%5D)+AND+%22Physical+Review+A%22%5BJournal%5D)">Femtosecond Time-Resolved Raman Spectroscopy Using Stimulated Raman Scattering.</a> Physical Review A. 61 (1), 013808(2000).</li>
<li>Yoshizawa, M., Kubo, M., Kurosawa, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Ultrafast+Photoisomerization+in+DCM+Dye+Observed+by+New+Femtosecond+Raman+Spectroscopy%5BTitle%5D)+AND+%22Journal+of+Luminescence%22%5BJournal%5D)">Ultrafast Photoisomerization in DCM Dye Observed by New Femtosecond Raman Spectroscopy.</a> Journal of Luminescence. 87-89, 739-741 (2000).</li>
<li>Yoshizawa, M., Aoki, H., Hashimoto, H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Vibrational+Relaxation+of+the+2Ag%E2%80%93+Excited+State+in+All-Trans-%CE%B2-Carotene+Obtained+by+Femtosecond+Time-Resolved+Raman+Spectroscopy%5BTitle%5D)+AND+%22Physical+Review+B%22%5BJournal%5D)">Vibrational Relaxation of the 2Ag– Excited State in All-Trans-β-Carotene Obtained by Femtosecond Time-Resolved Raman Spectroscopy.</a> Physical Review B. 63 (18), 180301(2001).</li>
<li>McCamant, D. W., Kukura, P., Mathies, R. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Femtosecond+Broadband+Stimulated+Raman%3A+A+New+Approach+for+High-Performance+Vibrational+Spectroscopy%5BTitle%5D)+AND+%22Applied+Spectroscopy%22%5BJournal%5D)">Femtosecond Broadband Stimulated Raman: A New Approach for High-Performance Vibrational Spectroscopy.</a> Applied Spectroscopy. 57 (11), 1317-1323 (2003).</li>
<li>McCamant, D. W., Kukura, P., Yoon, S., Mathies, R. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Femtosecond+Broadband+Stimulated+Raman+Spectroscopy%3A+Apparatus+and+Methods%5BTitle%5D)+AND+%22Review+of+Scientific+Instruments%22%5BJournal%5D)">Femtosecond Broadband Stimulated Raman Spectroscopy: Apparatus and Methods.</a> Review of Scientific Instruments. 75 (11), 4971-4980 (2004).</li>
<li>Kukura, P., McCamant, D. W., Mathies, R. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Femtosecond+Stimulated+Raman+Spectroscopy%5BTitle%5D)+AND+%22Annual+Review+of+Physical+Chemistry%22%5BJournal%5D)">Femtosecond Stimulated Raman Spectroscopy.</a> Annual Review of Physical Chemistry. 58, 461-488 (2007).</li>
<li>Laimgruber, S., Schachenmayr, H., Schmidt, B., Zinth, W., Gilch, P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((A+Femtosecond+Stimulated+Raman+Spectrograph+for+the+Near+Ultraviolet%5BTitle%5D)+AND+%22Applied+Physics+B%22%5BJournal%5D)">A Femtosecond Stimulated Raman Spectrograph for the Near Ultraviolet.</a> Applied Physics B. 85 (4), 557-564 (2006).</li>
<li>Umapathy, S., Lakshmanna, A., Mallick, B. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Ultrafast+Raman+Loss+Spectroscopy%5BTitle%5D)+AND+%22Journal+of+Raman+Spectroscopy%22%5BJournal%5D)">Ultrafast Raman Loss Spectroscopy.</a> Journal of Raman Spectroscopy. 40 (3), 235-237 (2009).</li>
<li>Mallick, B., Lakshmanna, A., Umapathy, S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Ultrafast+Raman+Loss+Spectroscopy+%28URLS%29%3A+Instrumentation+and+Principle%5BTitle%5D)+AND+%22Journal+of+Raman+Spectroscopy%22%5BJournal%5D)">Ultrafast Raman Loss Spectroscopy (URLS): Instrumentation and Principle.</a> Journal of Raman Spectroscopy. 42 (10), 1883-1890 (2011).</li>
<li>Kloz, M., van Grondelle, R., Kennis, J. T. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Wavelength-Modulated+Femtosecond+Stimulated+Raman+Spectroscopy-Approach+towards+Automatic+Data+Processing%5BTitle%5D)+AND+%22Physical+Chemistry+Chemical+Physics%22%5BJournal%5D)">Wavelength-Modulated Femtosecond Stimulated Raman Spectroscopy-Approach towards Automatic Data Processing.</a> Physical Chemistry Chemical Physics. 13 (40), 18123-18133 (2011).</li>
<li>Kloz, M., Weißenborn, J., Polívka, T., Frank, H. A., Kennis, J. T. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Spectral+Watermarking+in+Femtosecond+Stimulated+Raman+Spectroscopy%3A+Resolving+the+Nature+of+the+Carotenoid+S%2A+State%5BTitle%5D)+AND+%22Physical+Chemistry+Chemical+Physics%22%5BJournal%5D)">Spectral Watermarking in Femtosecond Stimulated Raman Spectroscopy: Resolving the Nature of the Carotenoid S* State.</a> Physical Chemistry Chemical Physics. 18 (21), 14619-14628 (2016).</li>
<li>Kuramochi, H., Takeuchi, S., Tahara, T. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Ultrafast+Structural+Evolution+of+Photoactive+Yellow+Protein+Chromophore+Revealed+by+Ultraviolet+Resonance+Femtosecond+Stimulated+Raman+Spectroscopy%5BTitle%5D)+AND+%22Journal+of+Physical+Chemistry+Letters%22%5BJournal%5D)">Ultrafast Structural Evolution of Photoactive Yellow Protein Chromophore Revealed by Ultraviolet Resonance Femtosecond Stimulated Raman Spectroscopy.</a> Journal of Physical Chemistry Letters. 3 (15), 2025-2029 (2012).</li>
<li>Wang, S., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Dynamic+High+Pressure+Induced+Strong+and+Weak+Hydrogen+Bonds+Enhanced+by+Pre-Resonance+Stimulated+Raman+Scattering+in+Liquid+Water%5BTitle%5D)+AND+%22Optics+Express%22%5BJournal%5D)">Dynamic High Pressure Induced Strong and Weak Hydrogen Bonds Enhanced by Pre-Resonance Stimulated Raman Scattering in Liquid Water.</a> Optics Express. 25 (25), 31670-31677 (2017).</li>
<li>Ashner, M. N., Tisdale, W. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((High+Repetition-Rate+Femtosecond+Stimulated+Raman+Spectroscopy+with+Fast+Acquisition%5BTitle%5D)+AND+%22Optics+Express%22%5BJournal%5D)">High Repetition-Rate Femtosecond Stimulated Raman Spectroscopy with Fast Acquisition.</a> Optics Express. 26 (14), 18331-18340 (2018).</li>
<li>Quincy, T. J., Barclay, M. S., Caricato, M., Elles, C. G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Probing+Dynamics+in+Higher-Lying+Electronic+States+with+Resonance-Enhanced+Femtosecond+Stimulated+Raman+Spectroscopy%5BTitle%5D)+AND+%22Journal+of+Physical+Chemistry+A%22%5BJournal%5D)">Probing Dynamics in Higher-Lying Electronic States with Resonance-Enhanced Femtosecond Stimulated Raman Spectroscopy.</a> Journal of Physical Chemistry A. 122 (42), 8308-8319 (2018).</li>
<li>Taylor, M. A., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Delayed+Vibrational+Modulation+of+the+Solvated+GFP+Chromophore+into+a+Conical+Intersection%5BTitle%5D)+AND+%22Physical+Chemistry+Chemical+Physics%22%5BJournal%5D)">Delayed Vibrational Modulation of the Solvated GFP Chromophore into a Conical Intersection.</a> Physical Chemistry Chemical Physics. 21 (19), 9728-9739 (2019).</li>
<li>Cassabaum, A. A., Silva, W. R., Rich, C. C., Frontiera, R. R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Orientation+and+Polarization+Dependence+of+Ground-+and+Excited-State+FSRS+in+Crystalline+Betaine-30%5BTitle%5D)+AND+%22Journal+of+Physical+Chemistry+C%22%5BJournal%5D)">Orientation and Polarization Dependence of Ground- and Excited-State FSRS in Crystalline Betaine-30.</a> Journal of Physical Chemistry C. 123 (20), 12563-12572 (2019).</li>
<li><a target="_blank" href="http://scholar.google.com/scholar?hl=en&safe=off&q=%22Raman+Spectroscopy+%28The+Spectroscopical+Society+of+Japan%2C+Spectroscopy+Series+1%29%22">Raman Spectroscopy (The Spectroscopical Society of Japan, Spectroscopy Series 1)</a>. Hamaguchi, H., Iwata, K. , Kodansha. Tokyo, Japan. (2015).</li>
<li>Hashimoto, H., Koyama, Y. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((The+C%3DC+Stretching+Raman+Lines+of+%CE%B2-Carotene+Isomers+in+the+S1+State+as+Detected+by+Pump-Probe+Resonance+Raman+Spectroscopy%5BTitle%5D)+AND+%22Chemical+Physics+Letters%22%5BJournal%5D)">The C=C Stretching Raman Lines of β-Carotene Isomers in the S1 State as Detected by Pump-Probe Resonance Raman Spectroscopy.</a> Chemical Physics Letters. 154 (4), 321-325 (1989).</li>
<li>Noguchi, T., Hayashi, H., Tasumi, M., Atkinson, G. H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Solvent+Effects+on+the+ag+C%3DC+Stretching+Mode+in+the+21Ag-+Excited+State+of+%CE%B2-Carotene+and+Two+Derivatives%3A+Picosecond+Time-Resolved+Resonance+Raman+Spectroscopy%5BTitle%5D)+AND+%22Journal+of+Physical+Chemistry%22%5BJournal%5D)">Solvent Effects on the ag C=C Stretching Mode in the 21Ag- Excited State of β-Carotene and Two Derivatives: Picosecond Time-Resolved Resonance Raman Spectroscopy.</a> Journal of Physical Chemistry. 95 (8), 3167-3172 (1991).</li>
</ol>

The authors have nothing to disclose.

Crucial factors in femtosecond time-resolved near-IR multiplex stimulated Raman measurement 
To obtain time-resolved near-IR stimulated Raman spectra with a high signal-to-noise ratio, the probe spectrum should ideally have uniform intensity in the whole wavelength range. White-light continuum generation (section 2.5) is, therefore, one of the most crucial parts of time-resolved near-IR stimulated Raman experiments. In general, the probe spectrum becomes broad and flat as the intensity of the incide...

Raman spectroscopy is a powerful and versatile tool for investigating the structures of molecules in a wide variety of samples from simple gases, liquids, and solids to functional materials and biological systems. Raman scattering is significantly enhanced when the photon energy of the excitation light coincides with the electronic transition energy of a molecule. The resonance Raman effect enables us to selectively observe the Raman spectrum of a species in a sample composed of many kinds of molecules. Near-IR electronic transitions are drawing a lot of attention as a probe for investigating the excited-state dynamics of molecules with large &#960;-conjugated structures. The energy and lifetime of the lowest excited singlet state have been determined for several carotenoids, which have a long one-dimensional polyene chain1,2,3. The dynamics of neutral and charged excitations have been extensively investigated for various photoconductive polymers in films4,5,6,7, nanoparticles8, and solutions9,10,11. Detailed information on the structures of the transients will be obtainable if time-resolved near-IR Raman spectroscopy is applied to these systems. Only a few studies, however, have been reported on time-resolved near-IR Raman spectroscopy12,13,14,15,16, because the sensitivity of near-IR Raman spectrometers is extremely low. The low sensitivity principally originates from the low probability of near-IR Raman scattering. The probability of spontaneous Raman scattering is proportional to &#969;i&#969;s3, where &#969;i and &#969;s are the frequencies of the excitation light and the Raman scattering light, respectively. In addition, commercially available near-IR detectors have much lower sensitivity than CCD detectors functioning in the UV and visible regions.
Femtosecond time-resolved stimulated Raman spectroscopy has emerged as a new method of observing time-dependent changes of Raman active vibrational bands beyond the apparent Fourier-transform limit of a laser pulse17,18,19,20,21,22,23,24,25,26,27,28,29,30,31,32,33. Stimulated Raman scattering is generated by irradiation of two laser pulses: the Raman pump and probe pulses. Here it is assumed that the Raman pump pulse has a larger frequency than the probe pulse. When the difference between the frequencies of the Raman pump and probe pulses coincides with the frequency of a Raman active molecular vibration, the vibration is coherently excited for a large number of molecules in the irradiated volume. Nonlinear polarization induced by the coherent molecular vibration enhances the electric field of the probe pulse. This technique is particularly powerful for near-IR Raman spectroscopy, because stimulated Raman scattering can solve the problem of the sensitivity of time-resolved near-IR spontaneous Raman spectrometers. Stimulated Raman scattering is detected as intensity changes of the probe pulse. Even if a near-IR detector has a low sensitivity, stimulated Raman scattering will be detected when the probe intensity is sufficiently increased. The probability of stimulated Raman scattering is proportional to &#969;RP&#969;SRS, where &#969;RP and &#969;SRS are the frequencies of the Raman pump pulse and stimulated Raman scattering, respectively20. The frequencies for stimulated Raman scattering, &#969;RP and &#969;SRS, are equivalent to &#969;i and &#969;s for spontaneous Raman scattering, respectively. We have recently developed a femtosecond time-resolved near-IR Raman spectrometer using stimulated Raman scattering for investigating the structures and dynamics of short-lived transients photogenerated in &#960;-conjugate systems2,3,7,10. In this article, we present the technical details of our femtosecond time-resolved near-IR multiplex stimulated Raman spectrometer. Optical alignment, acquisition of time-resolved stimulated Raman spectra, and calibration and correction of recorded spectra are described. The excited-state dynamics of &#946;-carotene in toluene solution is studied as a representative application of the spectrometer.

<table><tbody><tr><td>1-Axis Translational Stage</td><td>OptSigma</td><td>TSD-401S</td><td>Products equivalent to this are used as well; for M22, L9, and CM in Figure 1A</td></tr><tr><td>20-cm Optical Delay Line</td><td>OptSigma</td><td>SGSP26-200</td><td>ODL1 in Figure 1A</td></tr><tr><td>3-Axis Translational Stage</td><td>OptSigma</td><td>TSD-405SL</td><td>For L8 in Figure 1A</td></tr><tr><td>3-Axis Translational Stage</td><td>Suruga Seiki</td><td>B72-40C</td><td>For FC in Figure 1A</td></tr><tr><td>5-cm Optical Delay Line</td><td>PMT</td><td>HRS-0050</td><td>ODL2 in Figure 1A</td></tr><tr><td>Al Concave Mirror</td><td>Thorlabs</td><td>CM254-050-G01</td><td>Focal length: 50 mm; CM in Figure 1A</td></tr><tr><td>Base Plate</td><td>Suruga Seiki</td><td>A21-6</td><td>Products equivalent to this are used as well; for M1-M32, BS1-BS3, L1-L10, I1-I17, P1-P2, HWP1-3, F1-F3, VND1-VND2, OC, BPF, HS, BBO, SP, CM, and FC in Figure 1A</td></tr><tr><td>BBO Crystal</td><td>EKSMA Optics</td><td>-</td><td>Type 1, &amp;theta; = 23.2 deg; BBO in Figure 1A</td></tr><tr><td>BK7 Plano-Concave Lens</td><td>OptSigma</td><td>SLB-25.4-50NIR2</td><td>Focal length: 50 mm; IR anti-reflection coating; L6 in Figure 1A</td></tr><tr><td>BK7 Plano-Convex Lens</td><td>OptSigma</td><td>SLB-25.4-150PIR2</td><td>Focal length: 150 mm; IR anti-reflection coating; L2, L3, L5 in Figure 1A</td></tr><tr><td>BK7 Plano-Convex Lens</td><td>OptSigma</td><td>SLB-25.4-100PIR2</td><td>Focal length: 100 mm; IR anti-reflection coating; L4 in Figure 1A</td></tr><tr><td>BK7 Plano-Convex Lens</td><td>OptSigma</td><td>SLB-25.4-200PIR2</td><td>Focal length: 200 mm; IR anti-reflection coating; L7 in Figure 1A</td></tr><tr><td>Broadband Dielectric Mirror</td><td>OptSigma</td><td>TFMS-25.4C05-2/7</td><td>M22-M25, M28, M29 in Figure 1A</td></tr><tr><td>Broadband Dielectric Mirror</td><td>Precision Photonics (Advanced Thin Films)</td><td>-</td><td>M26, M27, M30-M32 in Figure 1A</td></tr><tr><td>Broadband Half-Wave Plate</td><td>CryLight</td><td>-</td><td>HWP3 in Figure 1A</td></tr><tr><td>Color Glass Filter</td><td>HOYA</td><td>IR85</td><td>F1 in Figure 1A</td></tr><tr><td>Color Glass Filter</td><td>HOYA</td><td>RM100</td><td>F2 in Figure 1A</td></tr><tr><td>Color Glass Filter</td><td>Schott</td><td>BG39</td><td>F3 in Figure 1A</td></tr><tr><td>Computer</td><td>Dell</td><td>Vostro 200 Mini Tower</td><td>OS: Windows XP</td></tr><tr><td>Cyclohexane</td><td>Kanto Kagaku</td><td>07547-1B</td><td>HPLC grade</td></tr><tr><td>Data Analysis Software</td><td>Wavemetrics</td><td>Igor Pro 8</td><td></td></tr><tr><td>Dielectric Beamsplitter</td><td>LAYERTEC</td><td>-</td><td>Reflection : Transmission = 2 : 1; BS1 in Figure 1A</td></tr><tr><td>Dielectric Beamsplitter</td><td>LAYERTEC</td><td>-</td><td>Reflection : Transmission = 1 : 1; BS2, BS3 in Figure 1A</td></tr><tr><td>Dielectric Mirror</td><td>Precision Photonics&lt;br/&gt; (Advanced Thin Films)</td><td>-</td><td>M1-M8 in Figure 1A</td></tr><tr><td>Digital Oscilloscope</td><td>Tektronix</td><td>TDS3054B</td><td>500 MHz, 5 GS/s</td></tr><tr><td>Elastomer Tube</td><td>-</td><td>-</td><td>Figure 1E</td></tr><tr><td>Femtosecond Ti:sapphire Oscillator</td><td>Coherent</td><td>Vitesse 800-2</td><td>Wavelength: 800 nm, pulse duration: 100 fs, average power: 280 mW, repetition rate: 80 MHz; included in Ti:S in Figure 1A</td></tr><tr><td>Femtosecond Ti:sapphire Regenerative Amplifier</td><td>Coherent</td><td>Legend-Elite-F-HE</td><td>Wavelength: 800 nm, pulse duration: 100 fs, pulse energy: 3.5 mJ, repetition rate: 1 kHz; included in Ti:S in Figure 1A</td></tr><tr><td>Film Polarizer</td><td>OptSigma</td><td>SPFN-30C-26</td><td>P1 in Figure 1A</td></tr><tr><td>Glan-Taylor Prism</td><td>OptSigma</td><td>GYPB-10-10SN-3/7</td><td>P2 in Figure 1A</td></tr><tr><td>Gold Mirror</td><td>OptSigma</td><td>TFG-25C05-10</td><td>M9-M21 in Figure 1A</td></tr><tr><td>Half-Wave Plate</td><td>OptSigma</td><td>WPQ-7800-2M</td><td>HWP1 in Figure 1A</td></tr><tr><td>Harmonic Separator</td><td>Coherent</td><td>TOPAS-C HRs 410-540 nm</td><td>HS in Figure 1A</td></tr><tr><td>InGaAs Array Detector</td><td>Horiba</td><td>Symphony-IGA-512X1-50-1700-1LS</td><td>512 ch, Liquid nitrogen cooled</td></tr><tr><td>InGaAs PIN Photodiode</td><td>Hamamatsu Photonics</td><td>G10899-01K</td><td></td></tr><tr><td>IR Half-Wave Plate</td><td>OptiSource</td><td>-</td><td>HWP2 in Figure 1A</td></tr><tr><td>Iris</td><td>Suruga Seiki</td><td>F74-3N</td><td>Products equivalent to this are used as well; I1-I17 in Figure 1A</td></tr><tr><td>Lens Holder</td><td>OptSigma</td><td>LHF-25.4S</td><td>Products equivalent to this are used as well; for L1-L10 in Figure 1A</td></tr><tr><td>Magnetic Gear Pump</td><td>Micropump</td><td>184-415</td><td></td></tr><tr><td>Mirror Mount</td><td>Siskiyou</td><td>IM100.C2M6R</td><td>Products equivalent to this are used as well; for M1-M32, BS1-BS3, BBO, CM in Figure 1A</td></tr><tr><td>near-IR phosphor card</td><td>Thorlabs</td><td>VRC2</td><td></td></tr><tr><td>Nut</td><td>-</td><td>-</td><td>Figure 1E, M4; purchased from a DIY store</td></tr><tr><td>Optical Chopper</td><td>New Focus</td><td>3501</td><td>OC in Figure 1A</td></tr><tr><td>Optical Parametric Amplifier</td><td>Coherent</td><td>OPerA-F</td><td>OPA1 in Figure 1A</td></tr><tr><td>Optical Parametric Amplifier</td><td>Coherent</td><td>TOPAS-C</td><td>OPA2 in Figure 1A</td></tr><tr><td>Polarizer Holder</td><td>OptSigma</td><td>PH-30-ARS</td><td>Products equivalent to this are used as well; for P1-P2 and HWP1-3 In Figure 1A</td></tr><tr><td>Polyfluoroacetate Tube</td><td>-</td><td>-</td><td>Figure 1E</td></tr><tr><td>Post Holder</td><td>OptSigma</td><td>BRS-12-80</td><td>Products equivalent to this are used as well; for M1-M32, BS1-BS3, L1-L10, I1-I17, P1-P2, HWP1-3, F1-F3, VND1-VND2, OC, BPF, HS, BBO, SP, CM, and FC in Figure 1A</td></tr><tr><td>Quartz Flow Cell</td><td>Tosoh Quartz</td><td>T-70-UV-2</td><td>FC in Figure 1A</td></tr><tr><td>Quartz Plano-Concave Lens</td><td>OptSigma</td><td>SLSQ-25-50N</td><td>Focal length: 50 mm; L8 in Figure 1A</td></tr><tr><td>Quartz Plano-Convex Lens</td><td>OptSigma</td><td>SLSQ-25-100P</td><td>Focal length: 100 mm; L1, L9 in Figure 1A</td></tr><tr><td>Quartz Plano-Convex Lens</td><td>OptSigma</td><td>SLSQ-25-220P</td><td>Focal length: 220 mm; L10 in Figure 1A</td></tr><tr><td>Sapphire Plate</td><td>Pier Optics</td><td>-</td><td>3 mm thick; SP in Figure 1A</td></tr><tr><td>Si PIN Photodiode</td><td>Hamamatsu Photonics</td><td>S3883</td><td></td></tr><tr><td>Single Spectrograph</td><td>Horiba Jobin Yvon</td><td>iHR320</td><td>Focal length: 32 cm</td></tr><tr><td>Stainless Steel Rod</td><td>Suruga Seiki</td><td>A41-100</td><td>Products equivalent to this are used as well; for M1-M32, BS1-BS3, L1-L10, I1-I17, P1-P2, HWP1-3, F1-F3, VND1-VND2, OC, BPF, HS, BBO, SP, CM, and FC in Figure 1A</td></tr><tr><td>Stainless Steel Rod</td><td>Newport</td><td>J-SP-2</td><td>Figure 1E</td></tr><tr><td>Toluene</td><td>Kanto Kagaku</td><td>40180-1B</td><td>HPLC grade</td></tr><tr><td>U-Shaped Steel Plate</td><td>-</td><td>-</td><td>Figure 1E; purchased from a DIY store</td></tr><tr><td>Variable Neutral Density Filter (with a holder)</td><td>OptSigma</td><td>NDHN-100</td><td>VND1 in Figure 1A</td></tr><tr><td>Variable Neutral Density Filter (with a holder)</td><td>OptSigma</td><td>NDHN-U100</td><td>VND2 in Figure 1A</td></tr><tr><td>Visual Programming Language</td><td>National Instruments</td><td>LabVIEW 2009</td><td>The control software in this study is programmed in LabVIEW 2009</td></tr><tr><td>Volume-Grating Bandpass Filter</td><td>OptiGrate</td><td>BPF-1190</td><td>BPF in Figure 1A</td></tr><tr><td>&amp;beta;-Carotene</td><td>Wako Pure Chemical Industries</td><td>035-05531</td><td></td></tr></tbody></table>

ultrafast time-resolved near-ir stimulated raman measurements of functional &#960;-conjugate systems

Femtosecond time-resolved stimulated Raman spectroscopy is a promising method of observing the structural dynamics of short-lived transients with near infrared (near-IR) transitions, because it can overcome the low sensitivity of spontaneous Raman spectrometers in the near-IR region. Here, we describe technical details of a femtosecond time-resolved near-IR multiplex stimulated Raman spectrometer that we have recently developed. A description of signal generation and optimization, measurement, data acquisition, and calibration and correction of recorded data is provided as well. We present an application of our spectrometer to analyze the excited-state dynamics of &#946;-carotene in toluene solution. A C=C stretch band of &#946;-carotene in the second lowest excited singlet (S2) state and the lowest excited singlet (S1) state is clearly observed in the recorded time-resolved stimulated Raman spectra. The femtosecond time-resolved near-IR stimulated Raman spectrometer is applicable to the structural dynamics of &#960;-conjugate systems from simple molecules to complex materials.

Femtosecond time-resolved near-IR stimulated Raman spectroscopy was applied to &#946;-carotene in toluene solution. The concentration of the sample was 1 x 10-4 mol dm-3. The sample was photoexcited by the actinic pump pulse at 480 nm with a pulse energy of 1 &#956;J. Time-resolved stimulated Raman spectra of &#946;-carotene in toluene are shown in Figure 2A. The raw spectra contained strong Raman bands of the solvent toluene and a weak Raman band of &#...

Watch this Scientific Journal Video about Ultrafast Time-resolved Near-IR Stimulated Raman Measurements of Functional Ï€-conjugate Systems at JoVE.com

Ultrafast Time-resolved Near-IR Stimulated Raman Measurements of Functional &#960;-conjugate Systems

Details of signal generation and optimization, measurement, data acquisition, and data handling for a femtosecond time-resolved near-IR stimulated Raman spectrometer are described. A near infrared stimulated Raman study on the excited-state dynamics of &#946;-carotene in toluene is shown as a representative application.

Femtosecond time-resolved stimulated Raman spectroscopy is a promising method of observing the structural dynamics of short-lived transients with near ...

ultrafast-time-resolved-near-ir-stimulated-raman-measurements

Research

JoVE Journal

Chemistry

7.1K Views.  Gakushuin University. Details of signal generation and optimization, measurement, data acquisition, and data handling for a femtosecond time-resolved near-IR stimulated Raman spectrometer are described. A near infrared stimulated Raman study on the excited-state dynamics of β-carotene in toluene is shown as a representative application.

Video: Ultrafast Time-resolved Near-IR Stimulated Raman Measurements of Functional π-conjugate Systems

Rejection of Fluorescence Background in Resonance and Spontaneous Raman Microspectroscopy

Raman spectroscopy is often plagued by a strong fluorescent background, particularly for biological samples. If a sample is excited with a train of ultrafast pulses, a system that can temporally separate spectrally overlapping signals on a picosecond timescale can isolate promptly arriving Raman scattered light from late-arriving fluorescence light. Here we discuss the construction and operation of a complex nonlinear optical system that uses all-optical switching in the form of a low-power optical Kerr gate to isolate Raman and fluorescence signals. A single 808 nm laser with 2.4 W of average power and 80 MHz repetition rate is split, with approximately 200 mW of 808 nm light being converted to &lt; 5 mW of 404 nm light sent to the sample to excite Raman scattering. The remaining unconverted 808 nm light is then sent to a nonlinear medium where it acts as the pump for the all-optical shutter. The shutter opens and closes in 800 fs with a peak efficiency of approximately 5%. Using this system we are able to successfully separate Raman and fluorescence signals at an 80 MHz repetition rate using pulse energies and average powers that remain biologically safe. Because the system has no spare capacity in terms of optical power, we detail several design and alignment considerations that aid in maximizing the throughput of the system. We also discuss our protocol for obtaining the spatial and temporal overlap of the signal and pump beams within the Kerr medium, as well as a detailed protocol for spectral acquisition. Finally, we report a few representative results of Raman spectra obtained in the presence of strong fluorescence using our time-gating system.

We discuss the construction and operation of a complex nonlinear optical
system that uses ultrafast all-optical switching to isolate Raman from fluorescence
signals. Using this system we are able to successfully separate Raman and fluorescence
signals utilizing pulse energies and average powers that remain biologically safe.

Raman spectroscopy is often plagued by a strong fluorescent background, particularly for biological samples. If a sample is excited with a train of ...

Bioengineering

Proton Transfer and Protein Conformation Dynamics in Photosensitive Proteins by Time-resolved Step-scan Fourier-transform Infrared Spectroscopy

Monitoring the dynamics of protonation and protein backbone conformation changes during the function of a protein is an essential step towards understanding its mechanism. Protonation and conformational changes affect the vibration pattern of amino acid side chains and of the peptide bond, respectively, both of which can be probed by infrared (IR) difference spectroscopy. For proteins whose function can be repetitively and reproducibly triggered by light, it is possible to obtain infrared difference spectra with (sub)microsecond resolution over a broad spectral range using the step-scan Fourier transform infrared technique. With ~102-103 repetitions of the photoreaction, the minimum number to complete a scan at reasonable spectral resolution and bandwidth, the noise level in the absorption difference spectra can be as low as ~10-4, sufficient to follow the kinetics of protonation changes from a single amino acid. Lower noise levels can be accomplished by more data averaging and/or mathematical processing. The amount of protein required for optimal results is between 5-100 &#181;g, depending on the sampling technique used. Regarding additional requirements, the protein needs to be first concentrated in a low ionic strength buffer and then dried to form a film. The protein film is hydrated prior to the experiment, either with little droplets of water or under controlled atmospheric humidity. The attained hydration level (g of water / g of protein) is gauged from an IR absorption spectrum. To showcase the technique, we studied the photocycle of the light-driven proton-pump bacteriorhodopsin in its native purple membrane environment, and of the light-gated ion channel channelrhodopsin-2 solubilized in detergent.

Key steps of protein function, in particular backbone conformational changes and proton transfer reactions, often take place in the microsecond to millisecond time scale. These dynamical processes can be studied by time-resolved step-scan Fourier-transform infrared spectroscopy, in particular for proteins whose function is triggered by light.

Monitoring the dynamics of protonation and protein backbone conformation changes during the function of a protein is an essential step towards ...

Engineering

Resonance Raman Spectroscopy of Extreme Nanowires and Other 1D Systems

This paper briefly describes how nanowires with diameters corresponding to 1 to 5 atoms can be produced by melting a range of inorganic solids in the presence of carbon nanotubes. These nanowires are extreme in the sense that they are the limit of miniaturization of nanowires and their behavior is not always a simple extrapolation of the behavior of larger nanowires as their diameter decreases. The paper then describes the methods required to obtain Raman spectra from extreme nanowires and the fact that due to the van Hove singularities that 1D systems exhibit in their optical density of states, that determining the correct choice of photon excitation energy is critical. It describes the techniques required to determine the photon energy dependence of the resonances observed in Raman spectroscopy of 1D systems and in particular how to obtain measurements of Raman cross-sections with better than 8% noise and measure the variation in the resonance as a function of sample temperature. The paper describes the importance of ensuring that the Raman scattering is linearly proportional to the intensity of the laser excitation intensity. It also describes how to use the polarization dependence of the Raman scattering to separate Raman scattering of the encapsulated 1D systems from those of other extraneous components in any sample.

The paper describes a method for producing extreme nanowires by melt infiltration into carbon nanotubes and how 1D systems may be characterized and investigated using Resonance Raman Spectroscopy to determine vibrational and optical excitation energies.

This paper briefly describes how nanowires with diameters corresponding to 1 to 5 atoms can be produced by melting a range of inorganic solids in the ...

Direct Imaging of Laser-driven Ultrafast Molecular Rotation

We present a method for visualizing laser-induced, ultrafast molecular rotational wave packet dynamics. We have developed a new 2-dimensional Coulomb explosion imaging setup in which a hitherto-impractical camera angle is realized. In our imaging technique, diatomic molecules are irradiated with a circularly polarized strong laser pulse. The ejected atomic ions are accelerated perpendicularly to the laser propagation. The ions lying in the laser polarization plane are selected through the use of a mechanical slit and imaged with a high-throughput, 2-dimensional detector installed parallel to the polarization plane. Because a circularly polarized (isotropic) Coulomb exploding pulse is used, the observed angular distribution of the ejected ions directly corresponds to the squared rotational wave function at the time of the pulse irradiation. To create a real-time movie of molecular rotation, the present imaging technique is combined with a femtosecond pump-probe optical setup in which the pump pulses create unidirectionally rotating molecular ensembles. Due to the high image throughput of our detection system, the pump-probe experimental condition can be easily optimized by monitoring a real-time snapshot. As a result, the quality of the observed movie is sufficiently high for visualizing the detailed wave nature of motion. We also note that the present technique can be implemented in existing standard ion imaging setups, offering a new camera angle or viewpoint for the molecular systems without the need for extensive modification.

We present a protocol for creating a real-time movie of a molecular rotational wave packet using a high-resolution Coulomb explosion imaging setup.

We present a method for visualizing laser-induced, ultrafast molecular rotational wave packet dynamics. We have developed a new 2-dimensional Coulomb ...

Raman and IR Spectroelectrochemical Methods as Tools to Analyze Conjugated Organic Compounds

In the presented work, two spectroelectrochemical techniques are discussed as tools for the analysis of the structural changes occurring in the molecule on the vibrational level of energy. Raman and IR spectroelectrochemistry can be used for advanced characterization of the structural changes in the organic electroactive compounds. Here, the step-by-step analysis by means of Raman and IR spectroelectrochemistry is shown. Raman and IR spectroelectrochemical techniques provide complementary information about structural changes occurring during an electrochemical process, i.e. allows for the investigation of redox processes and their products. The examples of IR and Raman spectroelectrochemical analysis are presented, in which the products of the redox reactions, both in solution and solid state, are identified.

A protocol of step-by-step Raman and IR spectroelectrochemical analysis is presented.

In the presented work, two spectroelectrochemical techniques are discussed as tools for the analysis of the structural changes occurring in the molecule ...

Novel Techniques for Observing Structural Dynamics of Photoresponsive Liquid Crystals

We discuss in this article the experimental measurements of the molecules in liquid crystal (LC) phase using the time-resolved infrared (IR) vibrational spectroscopy and time-resolved electron diffraction. Liquid crystal phase is an important state of matter that exists between the solid and liquid phases and it is common in natural systems as well as in organic electronics. Liquid crystals are orientationally ordered but loosely packed, and therefore, the internal conformations and alignments of the molecular components of LCs can be modified by external stimuli. Although advanced time-resolved diffraction techniques have revealed picosecond-scale molecular dynamics of single crystals and polycrystals, direct observations of packing structures and ultrafast dynamics of soft materials have been hampered by blurry diffraction patterns. Here, we report time-resolved IR vibrational spectroscopy and electron diffractometry to acquire ultrafast snapshots of a columnar LC material bearing a photoactive core moiety. Differential-detection analyses of the combination of time-resolved IR vibrational spectroscopy and electron diffraction are powerful tools for characterizing structures and photoinduced dynamics of soft materials.

Here, we present the protocols of differential-detection analyses of time-resolved infrared vibrational spectroscopy and electron diffraction which enable observations of the deformations of local structures around photoexcited molecules in a columnar liquid crystal, giving an atomic perspective on the relationship between the structure and the dynamics of this photoactive material.

We discuss in this article the experimental measurements of the molecules in liquid crystal (LC) phase using the time-resolved infrared (IR) vibrational ...

Measurement of Ultrafast Vibrational Coherences in Polyatomic Radical Cations with Strong-Field Adiabatic Ionization

We present a pump-probe method for preparing vibrational coherences in polyatomic radical cations and probing their ultrafast dynamics. By shifting the wavelength of the strong-field ionizing pump pulse from the commonly used 800 nm into the near-infrared (1200-1600 nm), the contribution of adiabatic electron tunneling to the ionization process increases relative to multiphoton absorption. Adiabatic ionization results in predominant population of the ground electronic state of the ion upon electron removal, which effectively prepares a coherent vibrational state (&#34;wave packet&#34;) amenable to subsequent excitation. In our experiments, the coherent vibrational dynamics are probed with a weak-field 800 nm pulse and the time-dependent yields of dissociation products measured in a time-of-flight mass spectrometer. We present the measurements on the molecule dimethyl methylphosphonate (DMMP) to illustrate how using 1500 nm pulses for excitation enhances the amplitude of coherent oscillations in ion yields by a factor of 10 as compared to 800 nm pulses. This protocol may be implemented in existing pump-probe setups through the incorporation of an optical parametric amplifier (OPA) for wavelength conversion.

We present a protocol for probing ultrafast vibrational coherences in polyatomic radical cations that result in molecular dissociation.

We present a pump-probe method for preparing vibrational coherences in polyatomic radical cations and probing their ultrafast dynamics. By shifting the ...

Multiplex Chemical Imaging Based on Broadband Stimulated Raman Scattering Microscopy

Stimulated Raman scattering (SRS) microscopy is a nonlinear optical technique for label-free chemical imaging. This analytical tool delivers chemical maps at high speed, and high spatial resolution of thin samples by directly interrogating their molecular vibrations. In its standard implementation, SRS microscopy is narrowband and forms images with only a single vibrational frequency at a time. However, this approach not only hinders the chemical specificity of SRS but also neglects the wealth of information encoded within vibrational spectra. 
These limitations can be overcome by broadband SRS, an implementation capable of extracting a vibrational spectrum per pixel of the image in parallel. This delivers hyperspectral data that, when coupled with chemometric analysis, maximizes the amount of information retrieved from the specimen. Thus, broadband SRS improves the chemical specificity of the system, allowing the quantitative determination of the concentration of the different constituents of a sample. Here, we report a protocol for chemical imaging with broadband SRS microscopy, based on a home-built SRS microscope operating with a custom differential multichannel-lock-in amplifier detection. It discusses the sample preparation, alignment of the SRS apparatus, and chemometric analysis. By acquiring vibrational Raman spectra, the protocol illustrates how to identify different chemical species within a mixture, determining their relative concentrations.

We present a protocol to acquire chemical images with broadband stimulated Raman scattering (SRS) microscopy. Based on an SRS microscope that operates with differential multichannel-lock-in detection, the protocol describes the sample preparation, adjustment of the SRS apparatus, and chemometrics to disentangle different constituents of chemically heterogeneous samples.

Stimulated Raman scattering (SRS) microscopy is a nonlinear optical technique for label-free chemical imaging. This analytical tool delivers chemical maps ...

A Technical Guide for Performing Spectroscopic Measurements on Metal-Organic Frameworks

Metal-organic frameworks (MOFs) offer a unique platform to understand light-driven processes in solid-state materials, given their high structural tunability. However, the progression of MOF-based photochemistry has been hindered by the difficulty in spectrally characterizing these materials. Given that MOFs are typically larger than 100 nm in size, they are prone to excessive light scatter, thereby rendering data from valuable analytical tools like transient absorption and emission spectroscopy nearly uninterpretable. To gain meaningful insights of MOF-based photo-chemical and physical processes, special consideration must be taken toward properly preparing MOFs for spectroscopic measurements, as well as the experimental setups that garner higher quality data. With these considerations in mind, the present guide provides a general approach and set of guidelines for the spectroscopic investigation of MOFs. The guide addresses the following key topics: (1) sample preparation methods, (2) spectroscopic techniques/measurements with MOFs, (3) experimental setups, (3) control experiments, and (4) post-run stability characterization. With appropriate sample preparation and experimental approaches, pioneering advancements toward the fundamental understanding of light-MOF interactions are significantly more attainable.

Here, we use a polymer stabilizer to prepare metal-organic framework (MOF) suspensions that exhibit markedly decreased scatter in their ground-state and transient absorption spectra. With these MOF suspensions, the protocol provides various guidelines to characterize the MOFs spectroscopically to yield interpretable data.

Metal-organic frameworks (MOFs) offer a unique platform to understand light-driven processes in solid-state materials, given their high structural ...

Biomolecular Imaging of Cellular Uptake of Nanoparticles using Multimodal Nonlinear Optical Microscopy

Probing gold nanoparticles (AuNPs) in living systems is essential to reveal the interaction between AuNPs and biological tissues. Moreover, by integrating nonlinear optical signals such as stimulated Raman scattering (SRS), two-photon excited fluorescence (TPEF), and transient absorption (TA) into an imaging platform, it can be used to reveal biomolecular contrast of cellular structures and AuNPs in a multimodal manner. This article presents a multimodal nonlinear optical microscopy and applies it to perform chemically specific imaging of AuNPs in cancer cells. This imaging platform provides a novel approach for developing more efficient functionalized AuNPs and determining whether they are within vasculatures surrounding the tumor, pericellular, or cellular spaces.

This article presents the integration of a spectral-focusing module and a dual-output pulse laser, enabling rapid hyperspectral imaging of gold nanoparticles and cancer cells. This work aims to demonstrate the details of multimodal nonlinear optical techniques on a standard laser scanning microscope.

Probing gold nanoparticles (AuNPs) in living systems is essential to reveal the interaction between AuNPs and biological tissues. Moreover, by integrating ...

Ultrafast Time-resolved Near-IR Stimulated Raman Measurements of Functional π-conjugate Systems

Summary

Explore More Videos

PLAYLIST