Propagation Of Laser Pulses Research Articles

Optical modulation properties of the Ni-based layered double hydroxides for dual-wavelength Q-switched Er:YAP laser at 2.7 μm

The Nickel-vanadium layered double hydroxide (NiV-LDH) saturable absorber (SA) and the Nickel-cobalt layered double hydroxide (NiCo-LDH) SA were fabricated based on the liquid-phase exfoliation (LPE) method. The nonlinear optical modulation properties at 3 μm of the these two different SAs were investigated for the first time. The dual-wavelength Q-switched Er:YAP lasers at 2.7 μm were realized with the Ni-based LDH SAs. The shortest pulse duration of the generated dual-wavelength laser pulses was 141 ns with the peak power of 6.05 W and the repetition rate of 295 kHz, under the absorbed pump power of 4.8 W. The experimental results indicate the Ni-based LDHs can be the promising optical modulators for the 3-μm pulsed laser generation.

High-damage vanadium pentoxide film saturable absorber for sub-nanosecond Nd:YAG lasers

Low-dimensional materials as saturable absorber (SA) for sub-nanosecond pulse laser have attracted extensive attention due to their excellent optoelectronic properties. However, high-quality low-dimensional materials’ nonlinear optical properties, such as larger damage threshold and higher modulation depth, are essential for generation of stable sub-nanosecond pulse laser. Herein, the large-area high-quality vanadium pentoxide (V2O5) films were prepared by magnetron sputtering deposition technology, and the usage of V2O5 films as a SA for sub-nanosecond pulse passively Q-switched Nd:YAG laser generation for the first time. It was found that V2O5-SA films exhibit excellent nonlinear optical characteristics, with a larger damage threshold of 509.8 mJ/cm2 and a higher modulation depth of 21.8 %, and the shortest pulse width of 59 ns. Our experimental results demonstrate that V2O5-SA films has the advantages of larger damage threshold and stable availability, which provides a promising solution for the development of high-quality low-dimensional SA devices in short pulse solid-state lasers.

Q-switching pulse generation in multi-wavelength Brillouin Erbium-doped Fiber laser

Stimulated Brillouin scattering (SBS) was successfully used to induce Q-switching operation in a multi-wavelength Brillouin Erbium fiber laser (BEFL) operating in a long-wavelength band (L-band) regime. The SBS based self Q-switched laser used a 4.5 long highly nonlinear Erbium-doped fiber (EDF) as the hybrid gain medium to generate a multiple wavelength Q-switched pulses, which operated at the center wavelength of around 1603 nm. By changing the input pump power in a range from 59.1 mW to 162.2 mW, the repetition rate can be varied from 14.29 to 29.69 kHz and the pulse width can be grasped from 26.52 to 14.80 μs. Under 162.2 mW pump power, the maximum pulse energy was recorded at 96.0 nJ and the signal to noise ratio of the fundamental radio frequency was measured to be as high as 52.73 dB, which indicates the excellent stability of the SBS-based Q-switched laser. To the best of our knowledge, this is the first experiment of realizing a BEFL with Q-switched multi-wavelength output without any physical saturable absorber devices.

Self-starting coherent mode locking in a two-section laser with identical gain and absorber media

Coherent mode-locking (CML) represents a method for ultrashort pulse generation in lasers based on the self-induced transparency (SIT) phenomena, which allows us to overcome the principal limitations on the pulse duration imposed by the active medium's gain bandwidth in standard passively mode-locked lasers. So far, this regime was only studied in lasers with transition dipole moments in the absorber medium being twice larger than in the gain medium. This fact ensures that the $2\ensuremath{\pi}$-SIT-soliton in the absorber also forms the stable $\ensuremath{\pi}$-soliton in the gain but can be barely realized in experiments. In this paper we demonstrate theoretically that the self-starting stable coherent mode-locking regime can also arise if the same medium is used both in the gain and absorber laser sections, i.e., the transition dipole moments are equal. These results are both obtained analytically using the area theorem and confirmed by the numerical solution of the Maxwell-Bloch equations. Our findings can enable new opportunities in the area of ultrafast lasers.

Ultrafast L Band Soliton Pulse Generation in Erbium-Doped Fiber Laser Based on Graphene Oxide Saturable Absorber

We demonstrate a simple mode-locked Erbium-doped fiber laser (EDFL) based on self-synthesized saturable absorber (SA) by combining graphene oxide (GO) and polyethylene oxide (PEO) solutions to form a GO-PEO thin film. This thin film was incorporated into an Erbium-doped fiber laser (EDFL) with a cavity length of 9 m. Our EDFL could operate at a 22 MHz repetition rate with a 0.8 ps pulse duration. The laser also showed stable soliton pulses under various laser pump power values. Our reported results show that GO-PEO SA is effective and proven as a cost-effective material for saturable absorbers for EDFLs.

Searching for optimal THz generation through calculations of the asymmetry of photoelectron momentum distributions by an improved strong-field-approximation method

From the solution of the time-dependent Schr\"odinger equation (TDSE), it has been shown that in a two-color laser pulse the relative phase that optimizes terahertz (THz) radiation also optimizes the asymmetry of the angular distribution of photoelectrons. Here, we show that a second-order strong-field approximation can accurately calculate the asymmetry of photoelectrons and thus can locate the phase delay that optimizes THz generation, doing so four orders of magnitude faster than TDSE calculations. We further trace that this is possible because THz emission originates from a free-free radiative transition between the rescattered electron and the target ion, similar to other electron-ion collisions in the laser field, e.g., high-harmonic generation and nonsequential double ionization. Our results pave the way to locate the optimal phase delay for any typical laser pulses for maximal THz generation in the laboratory.

Exceeding the Boundaries of the Paraxial Spatiotemporal Nonlinear Optics and Filamentation for Ultrashort Laser Pulses.

An impressive phenomenon of observed plasma instability and conical emission under the propagation of ultrashort laser pulses in the air is reported. The discussed novel findings demonstrating nonlinear effects are incapable to be explained in the standard spatiotemporal paraxial optics. Three main mechanisms are investigated. The first one is related to the nonlinear nonparaxial mechanisms for waveguiding of femtosecond pulses, and the second one considers the mechanism of single filament formation at weak ionization. The third mechanism demonstrates a new physical effect leading to collision ionization with intensities in the range of 1010-1011 W/cm2. Furthermore, a new ionization regime of instability is suggested at intensities below the critical thresholds for multiphoton and tunnel ionization. The experimental results and findings are supported by theoretical analyses and numerical simulations.

Efficient combination and enhancement of high-power mid-infrared pulses in plasmas

High-power intense optical sources in the mid-to-long wavelength infrared region are very attractive for a wide range of fields from fundamental research to materials science and biology applications. However, there are still significant challenges in extending long-wavelength infrared pulses into the relativistic regime using conventional optical techniques. Here, based upon a new type of plasma-based optical method, we present an efficient scheme capable of combining several high-power long-wavelength infrared laser pulses into one single, more intense pulse, thus bringing the intensity of the output pulse to the relativistic regime. Such intense infrared pulses will open up new possibilities for strong-field physics and ultrafast applications. Furthermore, this is beneficial to understand the underlying physics and nonlinear processes of modulation, propagation and energy transfer of high-power intense laser pulses in plasmas.

Generation of Q-switched pulses based on GaSb saturable absorber in an Er-doped fiber laser

In this study, we report the use of GaSb as a saturable absorber (SA) material in an Er-doped fiber (EDF) laser. The GaSb-based SA is prepared through the magnetron sputtering deposition technology, wherein a thin GaSb film is deposited on a microfiber. The modulation depth, saturable intensity, and non-saturable loss of the SA are determined to be 5.45 %, 37.3 MW/cm2, and 29.12 %, respectively. Under the Q-switching working state, the repetition frequeny is tuned from 73.15 to 93.7 kHz, and the pulse duration is changed from 5.17 to 2.33 μs at a pumping power of 310 to 500 mW. The highest average output power is 21.8 mW, which corresponds to a single pulse energy of 233.67 nJ. The generated laser pulses are in a stable state with a signal to noise ratio (SNR) of 65 dB. These results confirm the potential of GaSb as a successful saturable absorber candiatiate for building pulsed fiber lasers and in ultrafast optics applications.

The condition of collapse stopping during propagation of high-power femtosecond laser pulses in an optical medium

The condition of collapse stopping during propagation of high-power femtosecond laser pulses in an optical medium

"Stealth Scripts": Ultrashort Pulse Laser Luminescent Microscale Encoding of Bulk Diamonds via Ultrafast Multi-Scale Atomistic Structural Transformations.

The ultrashort-laser photoexcitation and structural modification of buried atomistic optical impurity centers in crystalline diamonds are the key enabling processes in the fabrication of ultrasensitive robust spectroscopic probes of electrical, magnetic, stress, temperature fields, and single-photon nanophotonic devices, as well as in "stealth" luminescent nano/microscale encoding in natural diamonds for their commercial tracing. Despite recent remarkable advances in ultrashort-laser predetermined generation of primitive optical centers in diamonds even on the single-center level, the underlying multi-scale basic processes, rather similar to other semiconductors and dielectrics, are almost uncovered due to the multitude of the involved multi-scale ultrafast and spatially inhomogeneous optical, electronic, thermal, and structural elementary events. We enlighten non-linear wavelength-, polarization-, intensity-, pulsewidth-, and focusing-dependent photoexcitation and energy deposition mechanisms in diamonds, coupled to the propagation of ultrashort laser pulses and ultrafast off-focus energy transport by electron-hole plasma, transient plasma- and hot-phonon-induced stress generation and the resulting variety of diverse structural atomistic modifications in the diamond lattice. Our findings pave the way for new forthcoming groundbreaking experiments and comprehensive enlightening two-temperature and/or atomistic modeling both in diamonds and other semiconductor/dielectric materials, as well as innovative technological breakthroughs in the field of single-photon source fabrication and "stealth" luminescent nano/microencoding in bulk diamonds for their commercial tracing.

Theoretical Review of the Pulse Generation in Dual-Locked Semiconductor Lasers: Asymptotic and Numerical Computation

Theoretical Review of the Pulse Generation in Dual-Locked Semiconductor Lasers: Asymptotic and Numerical Computation

Generation and application of high-contrast laser pulses using plasma mirror in the SULF-1PW beamline

Generation and application of high-contrast laser pulses using plasma mirror in the SULF-1PW beamline

Pulse nonlinear compression generated 71.3 W femtosecond laser

<sec>The power of femtosecond lasers based on Ti: sapphire or Yb-doped gain media has reached a high level by using chirped pulse amplification. The dispersive elements are normally employed in CPA devices, thereby increasing the complexity and cost of the laser system. However, for the Nd-doped laser, its power can be amplified to hundreds of microjoules or even several millijoules directly without CPA technology. So compressing the picosecond pulse to obtain femtosecond laser pulses with hundreds of microjoules pulse energy by post-compression technology becomes meaningful. The pulsed post-compression technology is the combination of nonlinear spectral broadening and dispersion compensation. Currently, the most effective method of nonlinear spectral broadening is achieved through self-phase modulation. The multi-pass cell (MPC) device based on self-phase modulation for broadening spectral bandwidth has been extensively studied, since it was demonstrated. The MPC concept demonstrates significant practical benefits. Essentially, it requires only two curved mirrors and a Kerr medium in between, making it a cost-effective and easily implementable method. Moreover, the MPCs are robust, quite insensitive to beam pointing, and can evendeal with small mode mismatch without transmission losses. These favorable characteristics make MPCs very attractive not only for scientific applications, but also for commercial and facility laser systems where reliability is crucial. The striking progress of the technique in the past six years has made it possible to obtain high average power femtosecond laser.</sec><sec>In this work, we demonstrate the generation of a high average power femtosecond laser pulse by nonlinearly compressing the picosecond pulse in the Herriott multi-pass cell device, and the distribution of eigenmode is analyzed. With this efficient and robust scheme, the spectrum is broadened from 0.20 nm to 2.75 nm, with a broadening ratio of 13.75, and the pulse duration of a picosecond amplifier is compressed from 1.25 ps to 780 fs, with a compression factor of 16. The average power before and after pulse compression are 100 W and 71.3 W respectively, so the overall transmission reaches 71.3%. The present scheme offers a viable route to low-cost and simple-configuration high-power femtosecond lasers driven by Nd-doped picosecond amplifiers.</sec>

Optical beat notes assisted attosecond soft X-ray pulse generation in high-gain free electron lasers

Abstract Attosecond soft X-ray pulses are of great importance for the study of ultrafast electronic phenomena. In this paper, a feasible method is proposed to generate isolated fully coherent attosecond soft X-ray free electron laser via optical frequency beating. Two optical lasers with the opposite frequency chirps are used to induce a gradient frequency energy modulation, which helps to generate a gradually varied spacing electron pulse train. Subsequently, the undulator sections with electron beam delay lines are used to amplify the target ultra-short radiation. Numerical start-to-end simulations have been performed and the results demonstrate that an isolated soft X-ray pulse with the peak power of 330 GW and pulse duration of 620 as can be achieved by the proposed technique.

Scalable sub-cycle pulse generation by soliton self-compression in hollow capillary fibers with a decreasing pressure gradient

Advances in the generation of the shortest optical laser pulses down to the sub-cycle regime promise to break new ground in ultrafast science. In this work, we theoretically demonstrate the potential scaling capabilities of soliton self-compression in hollow capillary fibers with a decreasing pressure gradient to generate near-infrared sub-cycle pulses in very different dispersion and nonlinearity landscapes. Independently of input pulse, gas and fiber choices, we present a simple and general route to find the optimal self-compression parameters which result in high-quality pulses. The use of a decreasing pressure gradient naturally favors the self-compression process, resulting in shorter and cleaner sub-cycle pulses, and an improvement in the robustness of the setup when compared to the traditional constant pressure approach.

Statistical simulation of laser pulse propagation in cirrus clouds with accounting for multiple scattering

Statistical simulation of laser pulse propagation in cirrus clouds with accounting for multiple scattering

Comparative study of ultrashort single-pulse and multi-pulse driven laser wakefield acceleration

Laser wakefield acceleration (LWFA) is a promising technique to build compact and powerful particle accelerators. In such accelerators, the electric fields required to accelerate charged particles are sustained by electron density modulations in the plasma. The plasma wave modulating the electron density may be excited by an intense laser pulse. However, propagation of intense laser pulse in plasma is subject to various instabilities which result in significant losses of laser energy, reducing the efficiency of wakefield generation. Using a train of lower intensity pulses instead of a single higher intensity pulse appears to be a more efficient scheme for LWFA. Here we have studied this alternative scheme by applying an ultra-short femtosecond Gaussian laser beam consisting pulse train of a various number of pulses in different cases to underdense plasma. The plasma density modulation and strength of the resulting wakefield have been compared in various cases of multi-pulse and single-pulse lasers, for the same amount of input energies. Here we demonstrate that applying multi-laser pulses of optimally selected lower intensities and proper spacing leads to stronger wakefield generation and more efficient electron acceleration compared to the case of a single pulse of higher energy.

A diode‐pumped SnS2 passively Q‐switched Tm‐doped pulsed laser

AbstractIn this research, a diode‐pumped SnS2 passively Q‐switched (PQS) V‐type Tm‐doped pulsed laser was demonstrated. The continuous‐wave (CW) condition without SnS2 saturable absorber (SA) was investigated first. A maximum output power of 1.26W with a slope efficiency of 24.28% was derived at an absorbed pump power of 7.11W under an output coupling of 5%. With the as‐prepared SnS2 SA employed, a series of stable Q‐switched (QS) pulse trains were successfully realized. A minimum pulse width of 3.061 μs and a maximum repetition frequency of 70.42 kHz were generated through an output coupling of 5%, corresponding to a maximum output power of 621 mW. The delivered highest peak power and maximum single pulse energy were 2.90W and 12.41 μJ under an output coupling of 2.5%, respectively. These findings indicated that SnS2 was a promising modulator for 2 μm all‐solid‐state pulsed laser generation.

Influence of wind-roughed sea surface on detection performance of spaceborne oceanic lidar

The wind-roughed sea surface influences the propagation properties of the laser beam and consequently affects the detection accuracy of spaceborne oceanic lidar. A comprehensive analysis of this problem is lacking to date. Herein, the Cox and Munk surface model is applied to the spaceborne oceanic lidar radiative transfer emulator to solve this problem. The effects of wind-roughed sea surface on oceanic lidar laser pulse propagation properties, such as the deflection angle of the direction, the inaccuracy of the signal depth, and the recommended incident angles, are studied using this model. The relationships among the wind speed, the incident angle and the propagation properties of the laser beam when passing through the sea surface are established. The maximum possible error of detection depth is within 8.2% when the wind speed is below 15 m/s and the incident zenith angle is less than 30°. And it can be reduced to 1.8% by profile averaging, which reveals the spaceborne oceanic lidar is capable to detect the global ocean profile information effectively in windy conditions. Moreover, the recommended incident angles for an oceanic lidar system are 37° and 35°, when the effective reflectance of the whitecaps are 0.2 and 0.6, respectively. The conclusions of this paper have reference value for oceanic lidar remote sensing in practice.