Showing papers on "Femtosecond pulse shaping published in 2020"

Background-free imaging of chemical bonds by a simple and robust frequency-modulated stimulated Raman scattering microscopy

Abstract: Being able to image chemical bonds with high sensitivity and speed, stimulated Raman scattering (SRS) microscopy has made a major impact in biomedical optics. However, it is well known that the standard SRS microscopy suffers from various backgrounds, limiting the achievable contrast, quantification and sensitivity. While many frequency-modulation (FM) SRS schemes have been demonstrated to retrieve the sharp vibrational contrast, they often require customized laser systems and/or complicated laser pulse shaping or introduce additional noise, thereby hindering wide adoption. Herein we report a simple but robust strategy for FM-SRS microscopy based on a popular commercial laser system and regular optics. Harnessing self-phase modulation induced self-balanced spectral splitting of picosecond Stokes beam propagating in standard single-mode silica fibers, a high-performance FM-SRS system is constructed without introducing any additional signal noise. Our strategy enables adaptive spectral resolution for background-free SRS imaging of Raman modes with different linewidths. The generality of our method is demonstrated on a variety of Raman modes with effective suppressing of backgrounds including non-resonant cross phase modulation and electronic background from two-photon absorption or pump-probe process. As such, our method is promising to be adopted by the SRS microscopy community for background-free chemical imaging.

Randomly Spaced Phase-Only Transmission Combs for Femtosecond Pulse Shaping

Abstract: We present a new Randomized Multiple Independent Comb Shaping (RandoMICS) algorithm based on phase-only tailored transmission for ultrashort laser pulse replication. The benefit of this method is satellite-free generation of programmable laser pulse sequences. The result is achieved by creating a transmission function as a stochastic comb of disjoint segments of optical frequency continuum with numerically optimized segment width distribution. The algorithm is realized by generating a regular aperiodic comb and random permutations of its elements. Experimental demonstration is performed with an acousto-optic pulse shaper providing broadband multi-window transmission function with arbitrarily variable widths of the segments. Suppression of undesired satellite pulses by the factor of 8 is demonstrated as well as generating pulse replicas with extended usable delay range compared to phase-only pulse shaping with periodic transmission combs.

A Versatile THz Source from High-Brightness Electron Beams: Generation and Characterization

Abstract: Ultra-short electron bunches, such as those delivered by a high-brightness photo-injector, are suitable to produce high peak power THz radiation, both broad and narrow band, with sub-picosecond down to femtosecond pulse shaping. The features of this kind of source in the THz range of the electromagnetic spectrum are extremely appealing for frequency- and time-domain experiments in a wide variety of fields. The present manuscript will overview the method of generation and characterization of THz radiation produced by high-brightness electron beams, as those available at the SPARC_LAB test facility.

Fourier pulse shaper for high power fiber coupled lasers and supercontinuum sources

Abstract: Femtosecond pulse shaping, a widely used technology, enables the generation of light sources with arbitrary amplitude, phase and polarization in the ultrafast regime. This technology has seen applications in fiber and nonlinear optics, OCT, confocal microscopy, bandpass filtering etc. However, these shapers work primarily at low optical powers under the 100mW level, limited by in and out coupling optics, shaper configurations and optical design of the shaper. Recently, another exciting field of research has been high power fiber laser sources. Various high power fiber sources based on a variety of nonlinear phenomena such as high power supercontinuum sources, Raman lasers etc., have been demonstrated. However, owing to 10s of W class optical powers involved, Fourier shaping in this field has not been utilized effectively thereby limiting many potential applications. Here, we demonstrate a scalable design for a high power Fourier shaper in 4-f configuration capable of handling 20 W of CW lasers with a working bandwidth of over 450nm between 1-1.5 micron connecting the two very important Yb and Er emission windows. Our design implements a transmissive geometry thereby isolating input and output beams which is otherwise provided by fiber coupled circulators, a component unavailable at high power levels for a broadband source. Cladding mode stripping is effectively implemented to heat-sink the uncoupled laser light to ensure high power operations feasible. The design also takes accounts of modifications in fiber coupled collimators and amplitude masks to conform with the demands of high power fiber laser technology. © COPYRIGHT SPIE. Downloading of the abstract is permitted for personal use only.

Magnetization reversal more rapidly by using an ultrashort square-wave laser

Abstract: With the feature of low-power and ultrashort time magnetization manipulation, all optical magnetic switching (AOMS) has been propelled to the forefront in investigations. To further speed up the magnetization reversal, in this paper, based on the combination of heating and Inverse Faraday Effect (IFE), an ultrashort square-wave laser (USWL) pulse is explored to excite the reversal of magnetization in a Co/Pt system, and all the parameters necessary for our simulation are well within the current theoretical estimates. Simulation results show that the switching time of magnetization is 3 times faster than the using of a traditional ultrashort Gaussian wave laser (UGWL) under the same laser fluence F = 4 mJ/cm2 and pulse duration t0 = 35 fs, and the threshold of AOMS for the ferromagnet is 0.67 mJ/cm2. We furthermore demonstrate that the heat accumulating effect of a laser-pulse is an important factor that influences the switching time, and a USWL has a larger effect of heat accumulating than a UGWL. At present, the debate on the origin of helicity dependent AOMS is still going on, and the model we propose provide a guideline for achieving helicity dependent AOMS more rapidly. We believe that the results could potentially be used to the field of storage technology especially for the using of AOMS.

Ultrafast Polarization Twisting using Chip-scale Metasurfaces

Abstract: Dielectric metasurfaces enable control of the temporal profile of large bandwidth, near-infrared femtosecond pulses. Using this approach, we demonstrate shaping of the time-domain polarization state within a single pulse.

Common Pulse Retrieval Algorithm: A Fast and Universal Method to Retrieve Ultrashort Pulses

Abstract: In this work we present a common pulse retrieval algorithm (COPRA) that can be universally applied to many pulse measurement methods and compares favorably in terms of speed and accuracy to existing approaches.

Twisting Polarization of Ultrafast Pulses using Metasurfaces

Abstract: Dielectric metasurfaces enable control of the temporal profile of large bandwidth, near-infrared femtosecond pulses. Using this approach, we demonstrate shaping of the time-domain polarization state within a single pulse.

Vectorial Shaping of Ultrafast Pulses using Dielectric Metasurfaces

Abstract: We demonstrate a dielectric-metasurface-enabled pulse shaper able to tailor the temporal polarization of near-infrared femtosecond pulses over an ultrawide bandwidth, allowing three-dimensional vector-shaped pulses exhibiting rich time-evolving instantaneous polarization states within a single pulse

Single-Shot Measurement of Extreme Ultraviolet Free Electron Laser Pulses

Abstract: We demonstrate an all-optical approach for measuring spectrograms of individual FEL pulses by measuring a spectrally-resolved EUV-EUV-optical four-wave-mixing signal. We experimentally demonstrate that this is phase-sensitive can be applied to structured and unstable pulse trains.