We thank Drs. E. Cronin-Furman and M. Weitzman (Olympus Corporation of the Americas Scientific Solutions Group) for assistance in acquiring images. This work was supported by National Institutes of Health Grant K22CA181611 (to B.Q.S.) and the Richard and Susan Smith Family Foundation (Newton, M.A.) Smith Family Award for Excellence in Biomedical Research (to B.Q.S.).

<ol>
	<li>Savage, N. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Optical+parametric+oscillators.">Optical parametric oscillators.</a> Nature Photonics. 4, 124 (2010).</li><li>Xu, C., Wise, F. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Recent+advances+in+fibre+lasers+for+nonlinear+microscopy.">Recent advances in fibre lasers for nonlinear microscopy.</a> Nature Photonics. 7, 875 (2013).</li><li>Kieu, K., Wise, F. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=All-fiber+normal-dispersion+femtosecond+laser.">All-fiber normal-dispersion femtosecond laser.</a> Optics Express. 16, 11453-11458 (2008).</li><li>Fekete, J., Cserteg, A., Szip&#337;ocs, R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=All-fiber+all-normal+dispersion+ytterbium+ring+oscillator.">All-fiber all-normal dispersion ytterbium ring oscillator.</a> Laser Physics Letters. 6, 49-53 (2009).</li><li>Krolopp, &. #. 1. 9. 3. ;., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Handheld+nonlinear+microscope+system+comprising+a+2+MHz+repetition+rate,+mode-locked+Yb-fiber+laser+for+in+vivo+biomedical+imaging.">Handheld nonlinear microscope system comprising a 2 MHz repetition rate, mode-locked Yb-fiber laser for in vivo biomedical imaging.</a> Biomedical Optics Express. 7, 3531-3542 (2016).</li><li>Fermann, M. E., Hartl, I. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Ultrafast+fibre+lasers.">Ultrafast fibre lasers.</a> Nature Photonics. 7, 868-874 (2013).</li><li>Szczepanek, J., Karda&#347;, T. M., Michalska, M., Radzewicz, C., Stepanenko, Y. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Simple+all-PM-fiber+laser+mode-locked+with+a+nonlinear+loop+mirror.">Simple all-PM-fiber laser mode-locked with a nonlinear loop mirror.</a> Optics Letters. 40, 3500-3503 (2015).</li><li>Bowen, P., Singh, H., Runge, A., Provo, R., Broderick, N. G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Mode-locked+femtosecond+all-normal+all-PM+Yb-doped+fiber+laser+at+1060+nm.">Mode-locked femtosecond all-normal all-PM Yb-doped fiber laser at 1060 nm.</a> Optics Communications. 364, 181-184 (2016).</li><li>Chong, A., Buckley, J., Renninger, W., Wise, F. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=All-normal-dispersion+femtosecond+fiber+laser.">All-normal-dispersion femtosecond fiber laser.</a> Optics Express. 14, 10095-10100 (2006).</li><li>Kieu, K., Renninger, W., Chong, A., Wise, F. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Sub-100+fs+pulses+at+watt-level+powers+from+a+dissipative-soliton+fiber+laser.">Sub-100 fs pulses at watt-level powers from a dissipative-soliton fiber laser.</a> Optics Letters. 34, 593-595 (2009).</li><li>Wise, F. W. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Femtosecond+Fiber+Lasers+Based+on+Dissipative+Processes+for+Nonlinear+Microscopy.">Femtosecond Fiber Lasers Based on Dissipative Processes for Nonlinear Microscopy.</a> IEEE Journal of Selected Topics in Quantum Electronics. 18, 1412-1421 (2012).</li><li>Nielsen, C. K., Keiding, S. R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=All-fiber+mode-locked+fiber+laser.">All-fiber mode-locked fiber laser.</a> Optics Letters. 32, 1474 (2007).</li><li>Liu, Z., Ziegler, Z. M., Wright, L. G., Wise, F. W. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Megawatt+peak+power+from+a+Mamyshev+oscillator.">Megawatt peak power from a Mamyshev oscillator.</a> Optica. 4, 649-654 (2017).</li><li>Sidorenko, P., Fu, W., Wright, L. G., Olivier, M., Wise, F. W. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Self-seeded,+multi-megawatt,+Mamyshev+oscillator.">Self-seeded, multi-megawatt, Mamyshev oscillator.</a> Optics Letters. 43, 2672-2675 (2018).</li><li>Li, X., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=High-power+ultrafast+Yb:fiber+laser+frequency+combs+using+commercially+available+components+and+basic+fiber+tools.">High-power ultrafast Yb:fiber laser frequency combs using commercially available components and basic fiber tools.</a> Review of Scientific Instruments. 87, 093114 (2016).</li><li>Bale, B., Kieu, K., Kutz, J., Wise, F. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Transition+dynamics+for+multi-pulsing+in+mode-locked+lasers.">Transition dynamics for multi-pulsing in mode-locked lasers.</a> Optics Express. 17, 23137-23146 (2009).</li><li>Davoudzadeh, N., Ducourthial, G., Spring, B. Q. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Custom+fabrication+and+mode-locked+operation+of+a+femtosecond+fiber+laser+for+multiphoton+microscopy.">Custom fabrication and mode-locked operation of a femtosecond fiber laser for multiphoton microscopy.</a> Scientific Reports. 9, 4233 (2019).</li><li>Renninger, W., Chong, A., Wise, F. W. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Area+theorem+and+energy+quantization+for+dissipative+optical+solitons.">Area theorem and energy quantization for dissipative optical solitons.</a> Journal of the Optical Society of America. 27, 1978-1982 (2010).</li></ol>

The authors declare no competing interests.

The protocols outlined here synthesize know-how and expertise that have been common practice in the laser physics laboratory for decades, but which is frequently unfamiliar to many biomedical researchers. This work attempts to make this ultrafast fiber laser technology more accessible to the broader community. The ANDi fiber laser design is well-established, as first developed in seminal works by Wise and colleagues3. However, implementations of this technology by other groups have sometimes resul...

Solid state femtosecond (fs) pulsed lasers are widely used for microscopy and biological research. One typical example is the usage of multiphoton excitation (MPE) fluorescence microscopy, where high peak power and low average power are desired to facilitate the MPE process while minimizing photodamage mechanisms. Many high-performance solid-state lasers are commercially available, and when combined with an optical parametric oscillator (OPO), the laser wavelength can be tuned over a wide range1. For example, commercial oscillator-OPO systems generate &#60;120 fs pulse durations (typically with an 80 MHz pulse repetition rate) and &#62;1 W average power from 680 to 1,300 nm. However, the cost of these commercial tunable fs laser systems is significant (&#62;$200,000), and solid-state systems generally require water cooling and are not portable for clinical applications.
Ultrashort pulsed fiber laser technology has matured in the past few years. The cost of a commercial fs pulsed fiber laser is typically significantly lower than solid-state lasers, albeit without the capability of broad wavelength tuning afforded by the solid-state systems mentioned above. Note that fiber lasers can be paired with OPOs when desired (i.e., hybrid fiber-solid-state systems). The large surface-to-volume ratio of fiber laser systems enables efficient air cooling2. Hence, fiber lasers are more portable than solid-state systems due to their relatively small size and simplified cooling system. Further, fusion splicing of the fiber components reduces system complexity and mechanical drift in contrast to the free-space alignment of the optical components making up solid-state devices. All of these features make fiber lasers ideal for clinical applications. In fact, all-fiber lasers have been developed for low-maintenance operation3,4,5, and all-polarization-maintaining (PM)-fiber lasers are stable to environmental factors including changes in temperature and humidity as well as mechanical vibrations2,6,7,8.
Here, a method is presented to build a cost-efficient fs pulsed ANDi fiber laser with commercially available parts and standard fiber splicing techniques. Methods to characterize pulse repetition rate, duration, and coherence (full mode-lock) are also presented. The resulting fiber laser generates mode-locked pulses that can be compressed to 70 fs with a repetition rate of 31 MHz and a wavelength centered at 1,060 to 1,070 nm. The maximum power output from the laser cavity is approximately 1 W. The pulse physics of ANDi fiber lasers elegantly utilizes nonlinear polarization evolution intrinsic to optical fiber as a key component of the saturable absorber2,3,9,10,11. However, this means that the ANDi design is not easily implemented using PM fiber (although an all-PM fiber implementation of ANDi mode-locking has been reported, albeit with low power and ps pulse duration12). Thus, environmental stability requires significant engineering. Next generation fiber laser designs, such as the Mamyshev oscillator, have the potential to offer complete environmental stability as all-PM-fiber devices capable of an order-of-magnitude increase in intracavity pulse energy as well as offering significant decreases in pulse duration to enable applications that rely on broad pulse spectra13,14. Custom fabrication of these innovative new fs fiber laser designs requires know-how and fiber splicing experience.

<table><tbody><tr><td>Adapters, mirrors, posts, mounts, and translational stage (optomechanics)</td><td>Thorlabs</td><td>TR6-P5 (3x), AD12NT (2x), PFSQ20-03-M01, PFSQ05-03-M01, KMS, KM100C, KM100CL, KM200S, LT1, LT101, UPH2-P5, UPH3-P5 (2x)</td><td>Standard optical components</td></tr><tr><td>Advanced optical fiber cleaver</td><td>AFL</td><td>CT-100</td><td></td></tr><tr><td>Autocorrelator</td><td>Femtochrome</td><td>FR-103XL/IR/FA/CDA</td><td></td></tr><tr><td>Beamsplitter mount</td><td>Thorlabs</td><td>BSH1/M</td><td></td></tr><tr><td>Factory fusion splicer</td><td>AFL</td><td>FSM-100P</td><td></td></tr><tr><td>Fiber collimators</td><td>OZ Optics (Canada)</td><td>LPC-08-1064-6/125-S-1.6-7.5AS-60-X-1-2-HPC</td><td>3x</td></tr><tr><td>Fiber-coupled,high-speed photodiode detector</td><td>Thorlabs</td><td>DET08CFC</td><td></td></tr><tr><td>Free-space isolator</td><td>Thorlabs</td><td>IO-5-1050-HP</td><td></td></tr><tr><td>Free-space isolator</td><td>Thorlabs</td><td>IO-3D-1050-VLP</td><td></td></tr><tr><td>Half waveplate</td><td>Union Optics (China)</td><td>WPZ2312</td><td>2x</td></tr><tr><td>High power multimode fiber pump module</td><td>Gauss Lasers (China)</td><td>Pump-MM-976-10</td><td></td></tr><tr><td>High power pump and signal combiner</td><td>ITF Technology (Canada)</td><td>MMC02112DF1</td><td></td></tr><tr><td>Index matching gel</td><td>Thorlabs</td><td>G608N3</td><td></td></tr><tr><td>Optical spectrum analyzer</td><td>Keysight</td><td>Agilent 70951B</td><td></td></tr><tr><td>Oscilloscope</td><td>Keysight</td><td>Agilent 54845A</td><td></td></tr><tr><td>Passive double clad fiber(5/130 &amp;mu;m)</td><td>ITF Technology (Canada)</td><td>MMC02112DF1</td><td>3m, Included with combiner</td></tr><tr><td>Polarizing beamsplitter</td><td>Thorlabs</td><td>PBS253</td><td></td></tr><tr><td>Quarter waveplates</td><td>Union Optics (China)</td><td>WPZ4312</td><td>2x</td></tr><tr><td>Quartz birefringent filter plate</td><td>Newlight (Canada)</td><td>BIR1060</td><td></td></tr><tr><td>RF spectrum analyzer</td><td>Tektronix</td><td>RSA306B</td><td></td></tr><tr><td>Single mode fiber (6/125 &amp;mu;m)</td><td>OZ Optics (Canada)</td><td>LPC-08-1064-6/125-S-1.6-7.5AS-60-X-1-2-HPC</td><td>1m, Included with collimators</td></tr><tr><td>Single mode fiber coupler</td><td>AFW (Australia)</td><td>FOSC-2-64-30-L-1-H64-2</td><td></td></tr><tr><td>Transmission diffraction grating 1</td><td>LightSmyth</td><td>T-1000-1040-3212-94</td><td>For compressor</td></tr><tr><td>Transmission diffraction grating 2</td><td>LightSmyth</td><td>T-1000-1040-60x12.3-94</td><td>For compressor</td></tr><tr><td>Waveplate rotation mount</td><td>Thorlabs</td><td>RSP1/M</td><td>4x</td></tr><tr><td>Ytterbium-doped single mode double clad fiber</td><td>Thorlabs</td><td>YB1200-6/125DC</td><td>3m</td></tr></tbody></table>

low-cost custom fabrication and mode-locked operation of an all-normal-dispersion femtosecond fiber laser for multiphoton microscopy

A protocol is presented to build a custom low-cost yet high-performance femtosecond (fs) fiber laser. This all-normal-dispersion (ANDi) ytterbium-doped fiber laser is built completely using commercially available parts, including $8,000 in fiber optic and pump laser components, plus $4,800 in standard optical components and extra-cavity accessories. Researchers new to fiber optic device fabrication may also consider investing in basic fiber splicing and laser pulse characterization equipment (~$63,000). Important for optimal laser operation, methods to verify true versus apparent (partial or noise-like) mode-locked performance are presented. This system achieves 70 fs pulse duration with a center wavelength of approximately 1,070 nm and a pulse repetition rate of 31 MHz. This fiber laser exhibits the peak performance that may be obtained for an easily assembled fiber laser system, which makes this design ideal for research laboratories aiming to develop compact and portable fs laser technologies that enable new implementations of clinical multiphoton microscopy and fs surgery.

It is critical to verify mode-locked operation upon completion of the fiber laser fabrication procedures. Signatures of optimal fs pulse generation and laser stability are as follows: First, the output pulse may be sufficiently characterized by the instrumentation outlined in step 6. The pulse spectrum output from the laser oscillator should be centered near 1,070 nm with the characteristic cat-ear or Batman shape that indicates mode-locking as predicted by numerical simulation of ANDi pu...

Watch this Scientific Journal Video about Low-cost Custom Fabrication and Mode-locked Operation of an All-normal-dispersion Femtosecond Fiber Laser for Multiphoton Microscopy at JoVE.com

Low-cost Custom Fabrication and Mode-locked Operation of an All-normal-dispersion Femtosecond Fiber Laser for Multiphoton Microscopy

A method is presented to build a custom low-cost, mode-locked femtosecond fiber laser for potential applications in multiphoton microscopy, endoscopy, and photomedicine. This laser is built using commercially available parts and basic splicing techniques.

A protocol is presented to build a custom low-cost yet high-performance femtosecond (fs) fiber laser. This all-normal-dispersion (ANDi) ytterbium-doped ...

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Research

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Engineering

7.5K Views.  Northeastern University. A method is presented to build a custom low-cost, mode-locked femtosecond fiber laser for potential applications in multiphoton microscopy, endoscopy, and photomedicine. This laser is built using commercially available parts and basic splicing techniques.

Video: Low-cost Custom Fabrication and Mode-locked Operation of an All-normal-dispersion Femtosecond Fiber Laser for Multiphoton Microscopy

Fabrication and Characterization of Disordered Polymer Optical Fibers for Transverse Anderson Localization of Light

We develop and characterize a disordered polymer optical fiber that uses transverse Anderson localization as a novel waveguiding mechanism. The developed polymer optical fiber is composed of 80,000 strands of poly (methyl methacrylate) (PMMA) and polystyrene (PS) that are randomly mixed and drawn into a square cross section optical fiber with a side width of 250 &mu;m. Initially, each strand is 200 &mu;m in diameter and 8-inches long. During the mixing process of the original fiber strands, the fibers cross over each other; however, a large draw ratio guarantees that the refractive index profile is invariant along the length of the fiber for several tens of centimeters. The large refractive index difference of 0.1 between the disordered sites results in a small localized beam radius that is comparable to the beam radius of conventional optical fibers. The input light is launched from a standard single mode optical fiber using the butt-coupling method and the near-field output beam from the disordered fiber is imaged using a 40X objective and a CCD camera. The output beam diameter agrees well with the expected results from the numerical simulations. The disordered optical fiber presented in this work is the first device-level implementation of 2D Anderson localization, and can potentially be used for image transport and short-haul optical communication systems.

We develop and characterize a disordered polymer optical fiber that uses transverse Anderson localization as a novel waveguiding mechanism. This microstructured fiber can transport a small localized beam with a radius that is comparable to the beam radius of conventional optical fibers.

We develop and characterize a disordered polymer optical fiber that uses transverse Anderson localization as a novel waveguiding mechanism. The developed ...

Automation of Mode Locking in a Nonlinear Polarization Rotation Fiber Laser through Output Polarization Measurements

When a laser is mode-locked, it emits a train of ultra-short pulses at a repetition rate determined by the laser cavity length. This article outlines a new and inexpensive procedure to force mode locking in a pre-adjusted nonlinear polarization rotation fiber laser. This procedure is based on the detection of a sudden change in the output polarization state when mode locking occurs. This change is used to command the alignment of the intra-cavity polarization controller in order to find mode-locking conditions. More specifically, the value of the first Stokes parameter varies when the angle of the polarization controller is swept and, moreover, it undergoes an abrupt variation when the laser enters the mode-locked state. Monitoring this abrupt variation provides a practical easy-to-detect signal that can be used to command the alignment of the polarization controller and drive the laser towards mode locking. This monitoring is achieved by feeding a small portion of the signal to a polarization analyzer measuring the first Stokes parameter. A sudden change in the read out of this parameter from the analyzer will occur when the laser enters the mode-locked state. At this moment, the required angle of the polarization controller is kept fixed. The alignment is completed. This procedure provides an alternate way to existing automating procedures that use equipment such as an optical spectrum analyzer, an RF spectrum analyzer, a photodiode connected to an electronic pulse-counter or a nonlinear detecting scheme based on two-photon absorption or second harmonic generation. It is suitable for lasers mode locked by nonlinear polarization rotation. It is relatively easy to implement, it requires inexpensive means, especially at a wavelength of 1550 nm, and it lowers the production and operation costs incurred in comparison to the above-mentioned techniques.

A protocol to detect and automate mode locking in a pre-adjusted nonlinear polarization rotation fiber laser is presented. The detection of a sudden change in the output polarization state when mode locking occurs is used to command the alignment of an intra-cavity polarization controller in order to find mode-locking conditions.

When a laser is mode-locked, it emits a train of ultra-short pulses at a repetition rate determined by the laser cavity length. This article outlines a ...

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 ...

Chemistry

Fabrication of 1-D Photonic Crystal Cavity on a Nanofiber Using Femtosecond Laser-induced Ablation

We present a protocol for fabricating 1-D Photonic Crystal (PhC) cavities on subwavelength-diameter tapered optical fibers, optical nanofibers, using femtosecond laser-induced ablation. We show that thousands of periodic nano-craters are fabricated on an optical nanofiber by irradiating with just a single femtosecond laser pulse. For a typical sample, periodic nano-craters with a period of 350 nm and with diameter gradually varying from 50 - 250 nm over a length of 1 mm are fabricated on a nanofiber with diameter around 450 - 550 nm. A key aspect of such a nanofabrication is that the nanofiber itself acts as a cylindrical lens and focuses the femtosecond laser beam on its shadow surface. Moreover, the single-shot fabrication makes it immune to mechanical instabilities and other fabrication imperfections. Such periodic nano-craters on nanofiber, act as a 1-D PhC and enable strong and broadband reflection while maintaining the high transmission out of the stopband. We also present a method to control the profile of the nano-crater array to fabricate apodized and defect-induced PhC cavities on the nanofiber. The strong confinement of the field, both transverse and longitudinal, in the nanofiber-based PhC cavities and the efficient integration to the fiber networks, may open new possibilities for nanophotonic applications and quantum information science.

We present a protocol for fabricating 1-D photonic crystal cavities on subwavelength diameter silica fibers (optical nanofibers) using femtosecond laser-induced ablation.

We present a protocol for fabricating 1-D Photonic Crystal (PhC) cavities on subwavelength-diameter tapered optical fibers, optical nanofibers, using ...

An Experimental Protocol for Femtosecond NIR/UV - XUV Pump-Probe Experiments with Free-Electron Lasers

This protocol describes key steps in performing and analyzing femtosecond pump-probe experiments that combine a femtosecond optical laser with a free-electron laser. This includes methods to establish the spatial and temporal overlap between the optical and free-electron laser pulses during the experiment, as well as important aspects of the data analysis, such as corrections for arrival time jitter, which are necessary to obtain high-quality pump-probe data sets with the best possible temporal resolution. These methods are demonstrated for an exemplary experiment performed at the FLASH (Free-electron LASer Hamburg) free-electron laser in order to study ultrafast photochemistry in gas-phase molecules by means of velocity map ion imaging. However, most of the strategies are also applicable to similar pump-probe experiments using other targets or other experimental techniques.

This protocol describes the key steps for performing and analyzing pump-probe experiments combining a femtosecond optical laser with a free-electron laser in order to study ultrafast photochemical reactions in gas-phase molecules.

This protocol describes key steps in performing and analyzing femtosecond pump-probe experiments that combine a femtosecond optical laser with a ...

Femtosecond Laser Filaments for Use in Sub-Diffraction-Limited Imaging and Remote Sensing

Probing remote matter with laser light is a ubiquitous technique used in circumstances as diverse as laser-induced breakdown spectroscopy and barcode scanners. In classical optics, the intensity that can be brought to bear on a remote target is limited by the spot size of the laser at the distance of the target. This spot size has a lower bound determined by the diffraction limit of classical optics. However, amplified femtosecond laser pulses generate intensity sufficient to modify the refractive index of the ambient air and undergo self-focusing. This self-focusing effect leads to the generation of highly intense laser filaments which maintain their intensity and small sub-millimeter diameter size at distances well beyond the classical Rayleigh length. Such intensity provides the capability of remote scanning, imaging, sensing, and spectroscopy with enhanced spatial resolution. We describe a technique for generating filaments with a femtosecond regenerative chirped-pulse amplifier, and for using the resulting filament to conduct imaging and spectroscopic measurements at remote distances of at least several meters.

High-intensity femtosecond pulses of laser light can undergo cycles of Kerr self-focusing and plasma defocusing, propagating an intense sub-millimeter-diameter beam over long distances. We describe a technique for generating and using these filaments to perform remote imaging and sensing beyond the classical diffraction limits of linear optics.

Probing remote matter with laser light is a ubiquitous technique used in circumstances as diverse as laser-induced breakdown spectroscopy and barcode ...

20 mJ, 1 ps Yb:YAG Thin-disk Regenerative Amplifier

This is a report on a 100 W, 20 mJ, 1 ps Yb:YAG thin-disk regenerative amplifier. A homemade Yb:YAG thin-disk, Kerr-lens mode-locked oscillator with turn-key performance and microjoule-level pulse energy is used to seed the regenerative chirped-pulse amplifier. The amplifier is placed in airtight housing. It operates at room temperature and exhibits stable operation at a 5 kHz repetition rate, with a pulse-to-pulse stability less than 1%. By employing a 1.5 mm-thick beta barium borate crystal, the frequency of the laser output is doubled to 515 nm, with an average power of 70 W, which corresponds to an optical-to-optical efficiency of 70%. This superior performance makes the system an attractive pump source for optical parametric chirped-pulse amplifiers in the near-infrared and mid-infrared spectral range. Combining the turn-key performance and the superior stability of the regenerative amplifier, the system facilitates the generation of a broadband, CEP-stable seed. Providing the seed and pump of the optical parametric chirped-pulse amplification (OPCPA) from one laser source eliminates the demand of active temporal synchronization between these pulses. This work presents a detailed guide to set up and operate a Yb:YAG thin-disk regenerative amplifier, based on chirped-pulse amplification (CPA), as a pump source for an optical parametric chirped-pulse amplifier.

A protocol for the operation of a high-energy, high-power optical parametric chirped pulse amplifier pump source based on an Yb:YAG thin-disk regenerative amplifier is presented here.

This is a report on a 100 W, 20 mJ, 1 ps Yb:YAG thin-disk regenerative amplifier. A homemade Yb:YAG thin-disk, Kerr-lens mode-locked oscillator with ...

Bioengineering

Conducting Multiple Imaging Modes with One Fluorescence Microscope

Fluorescence microscopy is a powerful tool to detect biological molecules in situ and monitor their dynamics and interactions in real-time. In addition to conventional epi-fluorescence microscopy, various imaging techniques have been developed to achieve specific experimental goals. Some of the widely used techniques include single-molecule fluorescence resonance energy transfer (smFRET), which can report conformational changes and molecular interactions with angstrom resolution, and single-molecule detection-based super-resolution (SR) imaging, which can enhance the spatial resolution approximately ten&#160;to twentyfold compared to diffraction-limited microscopy. Here we present a customer-designed integrated system, which merges multiple imaging methods in one microscope, including conventional epi-fluorescent imaging, single-molecule detection-based SR imaging, and multi-color single-molecule detection, including smFRET imaging. Different imaging methods can be achieved easily and reproducibly by switching optical elements. This set-up is easy to adopt by any research laboratory in biological sciences with a need for routine and diverse imaging experiments at a reduced cost and space relative to building separate microscopes for individual purposes.

Here we present a practical guide of building an integrated microscopy system, which merges conventional epi-fluorescent imaging, single-molecule detection-based super-resolution imaging, and multi-color single-molecule detection, including single-molecule fluorescence resonance energy transfer imaging, into one set-up in a cost-efficient way.

Fluorescence microscopy is a powerful tool to detect biological molecules in situ and monitor their dynamics and interactions in real-time. In addition to ...

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 ...

Photostimulation by Femtosecond Laser Activates Extracellular-signal-regulated Kinase (ERK) Signaling or Mitochondrial Events in Target Cells

Direct control of cellular defined molecular events is important to life science. Recently, studies have demonstrated that femtosecond laser stimulation can simultaneously activate multiple cellular molecular signaling pathways. In this protocol, we show that through coupling femtosecond laser into a confocal microscope, cells can be stimulated precisely by the tightly-focused laser. Some molecular processes that can be simultaneously observed are subsequently activated. We present detailed protocols of the photostimulation to activate extracellular signal regulated kinase (ERK) signaling pathway in Hela cells. Mitochondrial flashes of reactive oxygen species (ROS) and other mitochondrial events can be also stimulated if focusing the femtosecond laser pulse on a certain mitochondrial tubular structure. This protocol includes pretreating cells before photostimulation, delivering the photostimulation by a femtosecond laser flash onto the target, and observing/identifying molecular changes afterwards. This protocol represents an all-optical tool for related biological researches.

Photostimulation by Femtosecond Laser Activates Extracellular-signal-regulated Kinase ERK Signaling or Mitochondrial Events in Target Cells

Tightly-focused femtosecond laser can deliver precise stimulation to cells by being coupled into a confocal microscopy enabling the real-time observation and photostimulation. The photostimulation can activate cell molecular events including ERK signaling pathway and mitochondrial flashes of reactive oxygen species.

Direct control of cellular defined molecular events is important to life science. Recently, studies have demonstrated that femtosecond laser stimulation ...