Compression Of Femtosecond Pulses Research Articles

Thermodynamic and nonlinear optical analysis of solid-state multipass cells for compression of picosecond pulses in the 2−μm range

Multipass cells (MPCs) recently emerged as a new femtosecond pulse compression technique for lasers with high pulse energy. While most of the work focused on the compression of near-infrared laser systems so far, we address the case of holmium-based gain materials, which offer an enormous potential in terms of pulse energy, yet can only host a very narrow bandwidth in the 2-$\ensuremath{\mu}\text{m}$ wavelength range. Compression into the few-cycle regime, therefore, requires at least a hundredfold spectral broadening. Specifically, we investigate the utility of four different solid-state materials in the MPC, namely, fused silica, sapphire, YAG, and diamond. Spectral broadening dynamics is numerically investigated using the $2D+1$-unidirectional pulse propagation equation. To this end, we put particular emphasis on the thermal properties of the nonlinear optical material, which turn out as a critical issue above 2-$\ensuremath{\mu}\text{m}$ wavelength. Solving the heat equation for each of the materials, we then estimate the maximum temperature at beam center. These considerations show that outside the near infrared, thermodynamic parameters of nonlinear optical materials become at least equally important as their optical properties. Among the four materials under test, in particular, diamond stands out as it combines highly favorable thermal properties with a large optical nonlinearity. Finally, a concomitant slow degradation of spatial coherence is monitored. Our findings provide an effective guideline for the design of high pulse-energy compressors at wavelengths of $2\phantom{\rule{0.16em}{0ex}}\ensuremath{\mu}\text{m}$ and beyond.

Spectral broadening for pulse compression using liquid alcohols

Although gases, and more recently solids, have been used to create few-cycle pulses, we explore using liquid alcohols for spectral broadening and femtosecond pulse compression. By using a series of 1 cm cuvettes filled with 1-decanol, we have compressed a pulse from 83.6 fs down to 31.3 fs with a spectrum capable of supporting 25 fs pulses without filamentation. We measure the nonlinear index of refraction for various liquids, measuring n 2 = (6.8 ± 0.5) × 10−20 m2 W−1 for 1-decanol. We demonstrate liquids to be a compact, simple, versatile, and cost-effective material to obtain broad spectra.

Generation of sub-100fs electron pulses for time-resolved electron diffraction using a direct synchronization method.

To investigate photoinduced phenomena in various materials and molecules, ultrashort pulsed x-ray and electron sources with high brightness and high repetition rates are required. The x-ray and electron's typical and de Broglie wavelengths are shorter than lattice constants of materials and molecules. Therefore, photoinduced structural dynamics on the femtosecond to picosecond timescales can be directly observed in a diffraction manner by using these pulses. This research created a tabletop ultrashort pulsed electron diffraction setup that used a femtosecond laser and electron pulse compression cavity that was directly synchronized to the microwave master oscillator (∼3GHz). A compressed electron pulse with a 1kHz repetition rate contained 228 000 electrons. The electron pulse duration was estimated to be less than 100fs at the sample position by using photoinduced immediate lattice changes in an ultrathin silicon film (50nm). The newly developed time-resolved electron diffraction setup has a pulse duration that is comparable to femtosecond laser pulse widths (35-100fs). The pulse duration, in particular, fits within the timescale of photoinduced phenomena in quantum materials. Our developed ultrafast time-resolved electron diffraction setup with a sub-100fs temporal resolution would be a powerful tool in material science with a combination of optical pump-probe, time-resolved photoemission spectroscopic, and pulsed x-ray measurements.

Slow light nanocoatings for ultrashort pulse compression

Transparent materials do not absorb light but have profound influence on the phase evolution of transmitted radiation. One consequence is chromatic dispersion, i.e., light of different frequencies travels at different velocities, causing ultrashort laser pulses to elongate in time while propagating. Here we experimentally demonstrate ultrathin nanostructured coatings that resolve this challenge: we tailor the dispersion of silicon nanopillar arrays such that they temporally reshape pulses upon transmission using slow light effects and act as ultrashort laser pulse compressors. The coatings induce anomalous group delay dispersion in the visible to near-infrared spectral region around 800 nm wavelength over an 80 nm bandwidth. We characterize the arrays’ performance in the spectral domain via white light interferometry and directly demonstrate the temporal compression of femtosecond laser pulses. Applying these coatings to conventional optics renders them ultrashort pulse compatible and suitable for a wide range of applications.

Femtosecond Pulse Compression With Pedestal Suppression in a Sagnac Interferometer Constructed of Anti-Resonant Hollow Core Fiber

In this paper, compression of high-power femtosecond pulses in Sagnac interferometers constructed of anti-resonant hollow core fibers (ARHCF) is investigated numerically and experimentally. By varying the types and pressures of gas filled in the hollow core fiber, the group velocity dispersion and the nonlinear pulse phase accumulation difference between clockwise and counterclockwise propagations could be tuned conveniently. In experiment, we demonstrate the pedestal suppression temporal pulse compression of 800 nm, 160 fs, 10 μJ pulses from a Ti: Sapphire laser at 1 kHz to 20 fs with maximum compression efficiency of 25% nearly and compression ratio of eight.

Modulational-instability-free pulse compression in anti-resonant hollow-core photonic crystal fiber.

Gas-filled hollow-core photonic crystal fiber (PCF) is used for efficient nonlinear temporal compression of femtosecond laser pulses, two main schemes being direct soliton-effect self-compression and spectral broadening followed by phase compensation. To obtain stable compressed pulses, it is crucial to avoid decoherence through modulational instability (MI) during spectral broadening. Here, we show that changes in dispersion due to spectral anti-crossings between the fundamental-core mode and core wall resonances in anti-resonant-guiding hollow-core PCF can strongly alter the MI gain spectrum, enabling MI-free pulse compression for optimized fiber designs. The results are important, since MI cannot always be suppressed by pumping in the normal dispersion regime.

Two-stage nonlinear compression of high-power femtosecond laser pulses

Two-stage compression of laser pulses with a power of 250 TW is experimentally realised by broadening their spectrum during self-phase modulation in fused silica and subsequent dispersion compensation upon reflection from chirping mirrors. A five-fold decrease in the duration is demonstrated, from 75 to 15 fs, with a B-integral value of about 5 at each stage. It is possible to avoid small-scale self-focusing due to self-filtering of the laser beam during free propagation in vacuum. With optimal parameters of the dispersive mirror, the pulse can be compressed to a duration of less than 5 fs.

Design and analysis of dispersion-compensating chalcogenide photonic crystal fiber with high birefringence

The photonic crystal fiber (PCF) with a bunch of air holes enclosing the silica core field has momentous and compelling attributes when compared with the ordinary single-mode fibers. In this work, both the birefringence and dispersion properties of a polarization-maintaining chalcogenide (ChG) photonic crystal fiber are numerically investigated by means of the finite element method. Through simulation, it is found that the birefringence of the proposed $${\mathrm{G}\mathrm{e}}_{11.5}{\mathrm{A}\mathrm{s}}_{24}{\mathrm{S}\mathrm{e}}_{64.5}$$ PCF can reach as high as $$0.03$$ when compared with the conventional fiber that has merely $$5\times {10}^{-4}$$ for wavelengths in the 2–10 $$\upmu \mathrm{m}$$ range. The PCF is designed with zero-dispersion wavelengths for x- and y-polarized modes in the 2–10 $$\upmu \mathrm{m}$$ range. It is also observed that over the entire MIR wavelength range, the GVD remains positive and has a maximum value of 30,000 ps2/nm-km. Hence, the proposed $${\mathrm{G}\mathrm{e}}_{11.5}{\mathrm{A}\mathrm{s}}_{24}{\mathrm{S}\mathrm{e}}_{64.5}$$ PCF plays the dual role of acting as a very good polarization-maintaining fiber due to its very high birefringence and an excellent dispersion-compensating fiber due to its large positive GVD. This $${\mathrm{G}\mathrm{e}}_{11.5}{\mathrm{A}\mathrm{s}}_{24}{\mathrm{S}\mathrm{e}}_{64.5}$$ PCF serves as a very good candidate for ultra-broadband high bit-rate transmission. Supercontinuum generation is another important application of PCF. Supercontinuum generation is a generation of coherent and broadband light. SC generation in PCFs has several applications in optical coherence tomography (OCT), optical frequency metrology (OFM), pulse compression, and design of ultrafast femtosecond laser pulses.

Compression of femtosecond pulses in a wide wavelength range using a large-mode-area tapered fiber

We report the design of a tapered fiber that can be used for the compression of pulses at different central wavelengths. The proposed fiber is a three-layer W-type large-mode-area fiber, which has been tapered to transform the mode area from 1700 µm2 to 900 µm2. We determine the exact length of the maximum pulse compression and numerically demonstrate the compression of a 250 fs, 100 kW peak power input pulse to 15 fs, 850 kW at 1.55 µm wavelength and compression of 250 fs, 120 kW peak power input pulses to 28 fs, 700 kW and to 46 fs, 500 kW at 1.8 µm and 2 µm wavelengths, respectively. Such a fiber can find wide ranging applications, including in communication, spectroscopy and medicine.

Generation of sub-two-cycle CEP-stable optical pulses at 3.5 μm by multiple-plate pulse compression for high-harmonic generation in crystals

Multiple-plate pulse compression of femtosecond mid-infrared pulses is demonstrated using YAG and Si windows. With this robust compression scheme, we produce sub-two-cycle, CEP-stable optical pulses and observe CEP-dependent high harmonic generation in crystals.

Using self-phase modulation for temporal compression of intense femtosecond laser pulses

We report a theoretical analysis of the spectrum broadening of intense chirped femtosecond pulses in media with cubic nonlinearity. Subsequent temporal compression of such pulses using a quadratic spectral phase corrector is investigated. Pulse compression from 57 fs to 22 fs is demonstrated experimentally in a petawatt laser beam.

All-fiber spectral compression of femtosecond pulse for coherent anti-Stokes Raman scattering excitation source

Coherent anti-Stokes Raman scattering (CARS) imaging of femtosecond pulses has been a research hotspot in recent years, but the wide spectrum of the femtosecond pulse limits the spectral resolution of CARS imaging. Spectral compression is considered as an effective method to solve this problem. In this work, an all-fiber chirp spectral compression method of graded-index multi-mode fiber/single-mode fiber (GI-MMF/SMF) structure based on fiber pre-chirp and self-phase modulation is presented. It can be used as a CARS excitation source to increase the spectral resolution of CARS imaging. In the section of numerical simulation, the mean group velocity dispersion value of GI-MMF is used as a numerical parameter of the chirp analysis, which is estimated by analyzing modes of GI-MMF. On one hand, the mode field distributions in GI-MMF are simulated numerically by the finite-difference time-domain method, and these different modes are divided into eight mode groups. On the other hand, the energy proportion of each mode group is regarded as a weight value. Then we can obtain a mean group velocity dispersion value of 50/125 m GI-MMF, which is -2.28710-5 fs2/nm, by calculating the sum of group velocity dispersion weight values of mode groups. The results of spectral compression with different length ratios of 50/125 m GI-MMF to 780HP SMF are also analyzed based on the generalized nonlinear Schrdinger equation and split-step Fourier algorithm. The spectral width of 2.486 nm and the compression ratio of 5.230 are calculated, when the length ratio of 50/125 m GI-MMF to 780HP SMF is 1.2. In the section of experiment, three kinds of GI-MMFs with different core diameters are used in the experiment, the influences of the core diameter and the length ratio of GI-MMF to 780HP SMF on the spectral compression are investigated. The results show that the spectral width of 2.243 nm, corresponding to the compression ratio of 5.796 is obtained, when the length ratio of 50/125 m GI-MMF to 780HP SMF is 1.2, which is consistent with the simulation result. Under the condition of the same length ratio, the use of 105/125 m GI-MMF can raise the compression ratio to 152.941, and the spectral width of output pulse is 0.085 nm. When the pulse is applied to CARS spectrum detection, the theoretical spectral resolution can be 1.386 cm-1. The experimental results show that the spectral compression way to improve spectral resolution of CARS imaging is effective. This spectral compression system is characterized by simple structure, and high and controllable compression ratio, which provides theoretical and experimental basis for the all-fiber high spectral resolution CARS excitation source research.

Spectral compression of femtosecond pulses using chirped volume Bragg gratings.

In this Letter, we demonstrate a 360 fold spectral bandwidth reduction of femtosecond laser pulses using the method of sum frequency generation of pulses with opposite chirps. The reduction has been achieved in a compact setup in which a single chirped volume Bragg grating replaces conventional stretcher and compressor units. Starting with 180 fs pulses, we have obtained, with a 30% overall efficiency, pulses longer than 100 ps with the spectral bandwidth of 0.23 cm-1 (7 GHz). We also discuss our method on theoretical grounds.

Liquid crystal-based tunable photonic crystals for pulse compression and signal enhancement in multiphoton fluorescence

A unique device to enhance the fluorescence excitation with a maximum signal gain of 15-fold is demonstrated here. A one-dimensional photonic crystal infiltrated with liquid crystal as a central defect layer is designed for the enhancement of multiphoton fluorescence. Based on the linear dispersion properties near the edge of photonic bandgap, compression of femtosecond laser pulses can be realized. In comparison to the typical fluorescence enhancement techniques, this novel method has easy on-chip compression of an excitation pulse, tunable device, bio-friendly design, low damage, and compensation-free characteristics. The photonic bandgap structure employed in this approach has tunable and strong enhancements in fluorescence that enable these devices to find a place in bio-imaging and biophotonic technologies.

Limitations in ionization-induced compression of femtosecond laser pulses due to spatio-temporal couplings.

It was recently proposed that ionization-induced self-compression could be used as an effective method to further compress femtosecond laser pulses propagating freely in a gas jet [He et al., Phys. Rev. Lett. 113, 263904 2014]. Here, we address the question of the homogeneity of the self-compression process and show experimentally that homogeneous self-compression down to 12fs can be obtained by finding the appropriate focusing geometry for the laser pulse. Simulations are used to reproduce the experimental results and give insight into the self-compression process and its limitations. Simulations suggest that the ionization process induces spatio-temporal couplings which lengthen the pulse duration at focus, possibly making this method ineffective for increasing the laser peak intensity.

Compression of 1030-nm femtosecond pulses after nonlinear spectral broadening in Corning® HI 1060 fiber: Theory and experiment

We present the design and implementation of femtosecond pulse compression at 1030 nm based on spectral broadening in single-mode fiber, followed by dispersion compensation using an optimized double-pass SF11 prism pair. The source laser produced 1030-nm 144-fs pulses which were coupled into Corning® HI 1060 fiber, whose length was chosen to be 40 cm by using a pulse propagation model based on solving the generalized nonlinear Schrodinger equation. A maximum broadening to 60-nm bandwidth was obtained, following which compression to 60 ± 3 fs duration was achieved by using a prism-pair separation of 1025 ± 5 mm. All Rights Reserved © 2015 Universidad Nacional Autonoma de Mexico, Centro de Ciencias Aplicadas y Desarrollo Tecnologico. This is an open access item distributed under the Creative Commons CC License BY-NC-ND 4.0.

Three-wave mixing mediated femtosecond pulse compression in β-barium borate.

Nonlinear pulse compression mediated by three-wave mixing is demonstrated for ultrashort Ti:sapphire pulses in a type II phase-matched β-barium borate (BBO) crystal using noncollinear geometry. 170 μJ pulses at 800 nm with a pulse duration of 74 fs are compressed at their sum frequency to 32 fs with 55 μJ of pulse energy. Experiments and computer simulations demonstrate the potential of sum-frequency pulse compression to match the group velocities of the interacting waves to crystals that were initially not considered in the context of nonlinear pulse compression.

All-bismuth fiber system for femtosecond pulse generation, compression, and energy scaling.

We demonstrate a 1.44-μm bismuth-doped master oscillator-power amplifier (MOPA) system for generating femtosecond pulses. The cavity of master oscillator comprises dispersion-compensating fiber for detuning the total dispersion to the normal regime and a carbon nanotube saturable absorber for triggering the mode-locked operation. The described multifunction bismuth fiber amplifier performs energy scaling, large spectral broadening, and pulse compression. The results show that the large chirp superimposed on the pulses in the bismuth oscillator with normal dispersion can be effectively suppressed in a subsequent bismuth power amplifier with anomalous dispersion and high nonlinearity, resulting in high-quality pulses with record duration of 240 fs. An all-fiber design provides a practical solution that avoids the need for supplementary pulse stretching and compression.

Experimental demonstration of selective compression of femtosecond pulses in the Laue scheme of the dynamical Bragg diffraction in 1D photonic crystals.

We present the experimental results of diffraction-induced temporal splitting of chirped femtosecond optical pulses under the dynamical Bragg diffraction in the Laue geometry. For the experiments we made a transparent, high quality porous-quartz based 1D photonic crystal composed of 500 layers. We demonstrate that a selective compression of pulses is observed in this case, that is only one pulse from the pair is compressed, while the second one is broadened. This selective compression effect is determined by the sign and the value of the chirp parameter of the input pulse, in agreement with the theoretical description.

Silicon Nanowire Embedded Spiral Photonic Crystal Fiber for Soliton-Effect Pulse Compression

In this paper, we propose a new type of optical waveguide called silicon nanowire embedded equai-angular spiral photonic crystal fiber (SN-SPCF) using fully vectorial finite element method, where closely arranged arrays of air holes act as cladding and nanosize silicon material at the centre acts as core. We show that the proposed nanowire embedded PCF of 400 nm core diameter exhibits high anomalous group velocity dispersion (-3148 ps2/km), small third order dispersion (-8.6591 ps3/km) and high nonlinearity (443.2 W-1m-1) at 1550 nm wavelength. Soliton-effect pulse compression of femtosecond pulses in a silicon nanowire-spiral photonic crystal fiber at 1550 nm is numerically studied. We demonstrate a pulse compression of 75 fs input pulse to about 4 fs by the simultaneous actions of both linear effects (a large anomalous group velocity dispersion and a small third order dispersion) and the nonlinear effect (an effective high nonlinearity).