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/pubmed?term=((Optical+parametric+oscillators%5BTitle%5D)+AND+%22Nature+Photonics%22%5BJournal%5D)">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/pubmed?term=((Recent+advances+in+fibre+lasers+for+nonlinear+microscopy%5BTitle%5D)+AND+%22Nature+Photonics%22%5BJournal%5D)">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/pubmed?term=((All-fiber+normal-dispersion+femtosecond+laser%5BTitle%5D)+AND+%22Optics+Express%22%5BJournal%5D)">All-fiber normal-dispersion femtosecond laser.</a> Optics Express. 16, 11453-11458 (2008).</li>
<li>Fekete, J., Cserteg, A., Szipőocs, R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((All-fiber+all-normal+dispersion+ytterbium+ring+oscillator%5BTitle%5D)+AND+%22Laser+Physics+Letters%22%5BJournal%5D)">All-fiber all-normal dispersion ytterbium ring oscillator.</a> Laser Physics Letters. 6, 49-53 (2009).</li>
<li>Krolopp, Á, et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Handheld+nonlinear+microscope+system+comprising+a+2+MHz+repetition+rate%2C+mode-locked+Yb-fiber+laser+for+in+vivo+biomedical+imaging%5BTitle%5D)+AND+%22Biomedical+Optics+Express%22%5BJournal%5D)">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/pubmed?term=((Ultrafast+fibre+lasers%5BTitle%5D)+AND+%22Nature+Photonics%22%5BJournal%5D)">Ultrafast fibre lasers.</a> Nature Photonics. 7, 868-874 (2013).</li>
<li>Szczepanek, J., Kardaś, T. M., Michalska, M., Radzewicz, C., Stepanenko, Y. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Simple+all-PM-fiber+laser+mode-locked+with+a+nonlinear+loop+mirror%5BTitle%5D)+AND+%22Optics+Letters%22%5BJournal%5D)">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/pubmed?term=((Mode-locked+femtosecond+all-normal+all-PM+Yb-doped+fiber+laser+at+1060+nm%5BTitle%5D)+AND+%22Optics+Communications%22%5BJournal%5D)">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/pubmed?term=((All-normal-dispersion+femtosecond+fiber+laser%5BTitle%5D)+AND+%22Optics+Express%22%5BJournal%5D)">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/pubmed?term=((Sub-100+fs+pulses+at+watt-level+powers+from+a+dissipative-soliton+fiber+laser%5BTitle%5D)+AND+%22Optics+Letters%22%5BJournal%5D)">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/pubmed?term=((Femtosecond+Fiber+Lasers+Based+on+Dissipative+Processes+for+Nonlinear+Microscopy%5BTitle%5D)+AND+%22IEEE+Journal+of+Selected+Topics+in+Quantum+Electronics%22%5BJournal%5D)">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/pubmed?term=((All-fiber+mode-locked+fiber+laser%5BTitle%5D)+AND+%22Optics+Letters%22%5BJournal%5D)">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/pubmed?term=((Megawatt+peak+power+from+a+Mamyshev+oscillator%5BTitle%5D)+AND+%22Optica%22%5BJournal%5D)">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/pubmed?term=((Self-seeded%2C+multi-megawatt%2C+Mamyshev+oscillator%5BTitle%5D)+AND+%22Optics+Letters%22%5BJournal%5D)">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/pubmed?term=((High-power+ultrafast+Yb%3Afiber+laser+frequency+combs+using+commercially+available+components+and+basic+fiber+tools%5BTitle%5D)+AND+%22Review+of+Scientific+Instruments%22%5BJournal%5D)">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/pubmed?term=((Transition+dynamics+for+multi-pulsing+in+mode-locked+lasers%5BTitle%5D)+AND+%22Optics+Express%22%5BJournal%5D)">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/pubmed?term=((Custom+fabrication+and+mode-locked+operation+of+a+femtosecond+fiber+laser+for+multiphoton+microscopy%5BTitle%5D)+AND+%22Scientific+Reports%22%5BJournal%5D)">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/pubmed?term=((Area+theorem+and+energy+quantization+for+dissipative+optical+solitons%5BTitle%5D)+AND+%22Journal+of+the+Optical+Society+of+America%22%5BJournal%5D)">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 ...

low-cost-custom-fabrication-mode-locked-operation-an-all-normal

Universidad San Sebastian

Research

JoVE Journal

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

Microwave Photonics Systems Based on Whispering-gallery-mode Resonators

Microwave photonics systems rely fundamentally on the interaction between microwave and optical signals. These systems are extremely promising for various areas of technology and applied science, such as aerospace and communication engineering, sensing, metrology, nonlinear photonics, and quantum optics. In this article, we present the principal techniques used in our lab to build microwave photonics systems based on ultra-high Q whispering gallery mode resonators. First detailed in this article is the protocol for resonator polishing, which is based on a grind-and-polish technique close to the ones used to polish optical components such as lenses or telescope mirrors. Then, a white light interferometric profilometer measures surface roughness, which is a key parameter to characterize the quality of the polishing. In order to launch light in the resonator, a tapered silica fiber with diameter in the micrometer range is used. To reach such small diameters, we adopt the "flame-brushing" technique, using simultaneously computer-controlled motors to pull the fiber apart, and a blowtorch to heat the fiber area to be tapered. The resonator and the tapered fiber are later approached to one another to visualize the resonance signal of the whispering gallery modes using a wavelength-scanning laser. By increasing the optical power in the resonator, nonlinear phenomena are triggered until the formation of a Kerr optical frequency comb is observed with a spectrum made of equidistant spectral lines. These Kerr comb spectra have exceptional characteristics that are suitable for several applications in science and technology. We consider the application related to ultra-stable microwave frequency synthesis and demonstrate the generation of a Kerr comb with GHz intermodal frequency.

The customized techniques developed in our lab to build microwave photonics systems based on ultra-high Q whispering gallery mode resonators are presented. The protocols to obtain and characterize these resonators are detailed, and an explanation of some of their applications in microwave photonics is given.

Microwave photonics systems rely fundamentally on the interaction between microwave and optical signals. These systems are extremely promising for various ...

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 ...

Implementation of a Reference Interferometer for Nanodetection

A thermally and mechanically stabilized fiber interferometer suited for examining ultra-high quality factor microcavities is fashioned. After assessing its free spectral range (FSR), the module is put in parallel with a fiber taper-microcavity system and then calibrated through isolating and eliminating random shifts in the laser frequency (i.e. laser jitter noise). To realize the taper-microcavity junction and to maximize the optical power that is transferred to the resonator, a single-mode optical fiber waveguide is pulled. Solutions containing polystyrene nanobeads are then prepared and flown to the microcavity in order to demonstrate the system&#8217;s ability to sense binding to the surface of the microcavity. Data is post-processed via adaptive curve fitting, which allows for high-resolution measurements of the quality factor as well as the plotting of time-dependent parameters, such as resonant wavelength and split frequency shifts. By carefully inspecting steps in the time-domain response and shifting in the frequency-domain response, this instrument can quantify discrete binding events.

A reference interferometer technique, which is designed to remove undesirable laser jitter noise for nanodetection, is utilized for probing an ultra-high quality factor microcavity. Instructions for assembly, setup, and data acquisition are provided, alongside the measurement process for specifying the cavity quality factor.

A thermally and mechanically stabilized fiber interferometer suited for examining ultra-high quality factor microcavities is fashioned. After assessing ...

Fabrication and Testing of Microfluidic Optomechanical Oscillators

Cavity optomechanics experiments that parametrically couple the phonon modes and photon modes have been investigated in various optical systems including microresonators. However, because of the increased acoustic radiative losses during direct liquid immersion of optomechanical devices, almost all published optomechanical experiments have been performed in solid phase. This paper discusses a recently introduced hollow microfluidic optomechanical resonator. Detailed methodology is provided to fabricate these ultra-high-Q microfluidic resonators, perform optomechanical testing, and measure radiation pressure-driven breathing mode and SBS-driven whispering gallery mode parametric vibrations. By confining liquids inside the capillary resonator, high mechanical- and optical- quality factors are simultaneously maintained.

Parametric optomechanical excitations have recently been experimentally demonstrated in microfluidic optomechanical resonators by means of optical radiation pressure and stimulated Brillouin scattering. This paper describes the fabrication of these microfluidic resonators along with methodologies for generating and verifying optomechanical oscillations.

Cavity optomechanics experiments that parametrically couple the phonon modes and photon modes have been investigated in various optical systems including ...

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 ...

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 ...

Chemistry

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 ...

Fabrication of a Fabry-P&#233;rot Etalon for Application in Trace-Gas Spectroscopy

Fabrication of a Low-Cost, Fiber-Coupled, and Air-Spaced Fabry-P&#233;rot Etalon

Fabry-P&#233;rot etalons (FPE) have found their way into many applications. In fields such as spectroscopy, telecommunications, and astronomy, FPEs are used for their high sensitivity as well as their exceptional filtering capability. However, air-spaced etalons with high finesse are usually built by specialized facilities. Their production requires a clean room, special glass handling, and coating machinery, meaning commercially available FPEs are sold for a high price. In this article, a new and cost-effective method to fabricate fiber-coupled FPEs with standard photonic laboratory equipment is presented. The protocol should serve as a step-by-step guide for the construction and characterization of these FPEs. We hope this&#160;will enable researchers to conduct fast and cost-effective prototyping of FPEs for various fields of application. The FPE, as presented here, is used for spectroscopic applications. As shown in the representative results section via proof of principle measurements of water vapor in ambient air, this FPE has a finesse of 15, which is sufficient for the photothermal detection of trace concentrations of gases.

Author Spotlight: Fabrication of a Low-Cost, Fiber-Coupled, and Air-Spaced Fabry-P&#233;rot Etalon  

This protocol describes the construction of a low-cost, discrete, fiber-coupled, and air-spaced Fabry-Perot etalon with various applications, such as in trace-gas spectroscopy. The fabrication is possible in any facility with standard optical laboratory equipment available.

Fabry-P&#233;rot etalons (FPE) have found their way into many applications. In fields such as spectroscopy, telecommunications, and astronomy, FPEs are ...

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 ...