Pump Pulse Width Research Articles

High Peak Power Mini-array Quantum Cascade Lasers Operating in Pulsed Mode

Abstract Broad area quantum cascade lasers (BA QCLs) have significant applications in many areas, but suffer from demanding pulse operating conditions and poor beam quality due to heat accumulation and generation of high order modes. A structure of mini-array is adopted to improve the heat dissipation capacity and beam quality of BA QCLs. The active region is etched to form a multi emitter and the channels are filled with InP: Fe, which acts as a lateral heat dissipation channel to improve the lateral heat dissipation efficiency. A device with λ~4.8 μm, a peak output power of 122 W at 1.2% duty cycle with a pulse of 1.5 μs is obtained in room temperature, with far-field single-lobed distribution. This result allows BA QCLs to obtain high peak power at wider pump pulse widths and higher duty cycle conditions, promotes the application of the mid-infrared laser operating in pulsed mode in the field of standoff photoacoustic chemical detection, space optical communication and so on.

Enhancement of Q-Switched Erbium-Doped Fibre Laser Performance using Graphene Oxide-Calcium Oxide Thin Film Saturable Absorbers

This paper presents an experiment utilizing calcium oxide (CaO) from the cuttlefish bone combined with graphene oxide (GO) to create a graphene oxide-calcium oxide (GO-CaO) based saturable absorber (SA) for Q-switched erbium-doped fibre lasers. The experiment aims to investigate the impact of calcium oxide when added to graphene oxide to form the SA thin film. The laser performance of both types of SA was compared, considering their input pump power, repetition rate, pulse width, and output power. The results indicated that the graphene oxide – calcium oxide SA thin film provided the best output power and the lowest threshold input pump power at 10.76 µW and 53.12 mW, respectively. In the characterization, UV-Vis spectroscopy was utilized to determine the number of discrete wavelengths in UV or visible light that the materials absorbed or transmitted. The UV-Vis results indicated that the graphene oxide thin film exhibited an absorbance value of 0.049 AU and a transmittance value of 89.25 % at a wavelength of 1565 nm. In comparison, the GO-CaO SA thin film displayed an absorbance value of 0.037 AU and a transmittance value of 91.89 % at the same wavelength. Raman spectroscopy was also conducted to provide details about the chemical structure and crystallinity of the thin film samples. The results showed high-intensity peaks for the GO thin film at wavenumbers of 1353.74 cm-1 and 1609.85 cm-1, and for GO – CaO thin film at wavenumbers of 1358.56 cm-1 and 1612.18 cm-1. Additionally, SEM was utilized to study the morphology of the thin film samples. Based on the characterization and laser performance results, it was concluded that the addition of calcium oxide to graphene oxide enhances the properties of the SA thin film, leading to improved laser performance due to its higher thermal conductivity.

2.1–2.2 μm wavelength-tunable cascade gain modulation Raman fiber laser

We present a theoretical and experimental analysis of a mid-infrared wavelength-tunable cascade gain modulation Raman fiber laser. Our simulation model incorporates the Generalized Nonlinear Schrödinger Equation with the fiber Bragg grating transmission functions. Utilizing the pulse tracking method, we investigate and analyze the impact of pump pulse width and Raman gain fiber length on the first and second order Raman laser thresholds. Additionally, we exhibit the evolution process of the pulse and optical spectrum at a constant pump pulse energy. Furthermore, we present the output pulse width and energy, and the Raman laser center wavelength as a function of the pump pulse energy. Subsequently, using the optimal theoretical values of pump pulse width and Raman gain fiber length, we experimentally achieve the gain modulation Raman fiber laser. With a 1990 nm laser pumping, the Raman laser can produce a 2172 nm laser with a pulse width of 1.25 µs and a single pulse energy of approximately 400 nJ. When tuning the pump laser wavelength from 1950 nm to 2030 nm, the gain modulation Raman laser wavelength can vary from 2130 nm to 2215 nm. Importantly, our experimental results closely align with the theoretical predictions. This study provides valuable insights for the investigation of gain modulation Raman fiber lasers.

Characterization of sub-nanosecond pulse compression based on frequency-detuning SBS.

High-frequency, high-power picosecond lasers have important and wide-ranging applications in laser ranging, optoelectronic countermeasures, and ultrafine industrial processing. Pulse compression based on stimulated Brillouin scattering (SBS) can achieve a highly efficient picosecond laser output, while improving the peak power and beam quality of the laser. In this paper, a generator-amplifier two-cell structure with frequency-detuning was proposed to achieve a pulse output that combines high compression ratio and high energy reflectivity. The experiment proved that under a pump pulse width of 15 ns and repetition frequency of 10 Hz, when the generator cell and amplifier cell media were selected as HT-230, the highest energy reflectivity of 46% and narrowest compression pulse width of 1.1 ns were achieved, and the pulse compression ratio was 13.6. When the amplifier cell was selected as FC-770 and the generator cell was selected as HT-230, an energy reflectivity of 52% and a compression pulse width of 840 ps could be achieved simultaneously, and the pulse compression ratio was 18.

Comparing transmission- and epi-BCARS: a round robin on solid-state materials.

Broadband coherent anti-Stokes Raman scattering (BCARS) is a powerful spectroscopy method combining high signal intensity with spectral sensitivity, enabling rapid imaging of heterogeneous samples in biomedical research and, more recently, in crystalline materials. However, BCARS encounters spectral distortion due to a setup-dependent non-resonant background (NRB). This study assesses BCARS reproducibility through a round robin experiment using two distinct BCARS setups and crystalline materials with varying structural complexity, including diamond, 6H-SiC, KDP, and KTP. The analysis compares setup-specific NRB correction procedures, detected and NRB-removed spectra, and mode assignment. We determine the influence of BCARS setup parameters like pump wavelength, pulse width, and detection geometry and provide a practical guide for optimizing BCARS setups for solid-state applications.

Zero-broadening slow light from photorefractive two-wave mixing.

The ability to delay short light pulses is a promising solution for all-optical telecommunications, but suffers from a large distortion of the delayed pulse as a consequence of the high material dispersion. In this Letter, we demonstrate the possibility to all-optically control the group delay in a photorefractive (PR) crystal by the use of the two-wave mixing (TWM) effect in the pulse regime at room temperature. Most importantly, we show that a proper choice of the pump pulse width in the TWM process enables us to slow down shorter or longer signal pulses without distortion. The technique is demonstrated both at visible (638 nm) and infrared (1064 nm) wavelengths and for slowed-down pulses with durations ranging from 10 ns up to 30 ms, hence confirming its broad applicability.

Robust Pulse-Pumped Quadratic Soliton Assisted by Third-Order Nonlinearity

The generation of a quadratic soliton in a pulse-pumped microresonator has attracted significant interest in recent years. The strong second-order nonlinearity and high peak power of pumps offer a straightforward way to increase efficiency. In this case, the influence of the third-order nonlinearity effect becomes significant and cannot be ignored. In this paper, we study the quadratic soliton in a degenerate optical parametric oscillator driven synchronously by the pulse pump with third-order nonlinearity. Our simulations verify that the robustness of quadratic soliton generation is enhanced when the system experiences a perturbation from pump power, cavity detuning, and pump pulse width. These results represent a new way of manipulating frequency comb in resonant microphotonic structures.

Mid-IR supercontinuum generation in dispersion flattened As38Se62 chalcogenide photonic crystal fiber

We have created a PCF with square shaped core using chalcogenide material As38Se62 as core and air holes in IR region, which yield very high optical non linearity of 1290 W−1Km−1 at 3.5 μm, further gives a flat dispersion profile. The fiber has been used for numerically simulate SCG using low power pump pulse width (TFWHM) at 50 fs duration at 3.5 μm. At the end of 10 mm fiber, SC broadening of about 2000 to 12000 nm can be achieved with pulses of 4200 W peak power.

Enabling Variable High Spatial Resolution Retrieval From a Long Pulse BOTDA Sensor

Spatial resolution (SR) is one of the most important parameters of Brillouin optical time-domain analysis (BOTDA) sensors, which determines the minimum length that a perturbation event can be distinguished. In the field of Internet of Things (IoT), there is an urgent need for sensors with large-scale high-precision sensing capability for scenarios, such as intelligent monitoring of production lines and urban infrastructure. Conventionally, the SR is normally restricted to be longer than 1 m due to the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\sim 10$ </tex-math></inline-formula> -ns acoustic lifetime limitation in silica optical fibers. For long-distance smart monitoring systems, the SR is generally on the order of several meters or even worse. However, it does not meet the needs of many applications. Therefore, there is an urgent need to achieve SR in the submeter magnitude. In this work, for the first time to the best of our knowledge, we propose a convolutional neural network (CNN) to process the data of conventional BOTDA sensors, which achieves unprecedented performance improvement that allows to directly retrieve submeter SR from the sensing system that use long pump pulses. By using the simulated Brillouin gain spectrums (BGSs) as the CNN input and the corresponding high SR Brillouin frequency shift (BFS) as the output target, the trained CNN is able to obtain an SR higher than the theoretical value determined by the pump pulse width. In the experiment, the CNN accurately retrieves 0.5-m hotspots from the measured BGS with pump pulses from 20 to 50 ns, and the acquired BFS is in great agreement with 45/40 ns differential pulse-width pair (DPP) measurement results. Compared with the DPP technique, the proposed CNN demonstrates a twofold improvement in BFS uncertainty with only half the measurement time. In addition, by changing the training data sets, the proposed CNN can obtain tunable high SR retrieval based on conventional BOTDA sensors that use long pulses without any requirement of hardware modifications. It is worth mentioning that the proposed method is also applicable to larger pulse widths to retrieve a submeter SR. The proposed data post-processing approach paves the way to enable novel high SR BOTDA sensors, which brings substantial improvement over the state-of-the-art techniques in terms of system complexity, measurement time, reliability, etc.

Submetric Spatial Resolution ROTDR Temperature Sensor Assisted by Wiener Deconvolution.

A submetric spatial resolution Raman optical time-domain reflectometry (ROTDR) temperature sensor assisted by the Wiener deconvolution postprocessing algorithm has been proposed and experimentally demonstrated. Without modifying the typical configuration of the ROTDR sensor and the adopted pump pulse width, the Wiener demodulation algorithm is able to recover temperature perturbations of a smaller spatial scale by deconvoluting the acquired Stokes and anti-Stokes signals. Numerical simulations have been conducted to analyze the spatial resolution achieved by the algorithm. Assisted by the algorithm, a typical ROTDR sensor adopting pump pulses of 20 ns width can realize the distributed temperature sensing with a spatial resolution of 0.5 m and temperature accuracy of 1.99 °C over a 2.1-km sensing fiber.

962 nm LD end-pumped Er:YSGG cascade pulsed lasers at room temperature

We demonstrate a pulsed cascade laser on LD end-pumped Er:YSGG crystal near 1.6 and 2.8 μm at room temperature for the first time. The slope efficiency of mid-infrared laser with the assistance of cascade process is significantly improved. Under the working frequency of 100 Hz and pump pulse width of 6 ms, a maximum power of 243 mW centered at 2.79 μm is achieved with increasing slope efficiency of 4.2 %, while the slope efficiency of non-cascade is only 1.9 %. Under high pump power, four laser wavelengths of 2.793, 2.821, ∼2.860, and 2.918 μm are discovered and the phenomenon is explained according to the Boltzmann factors. This work would be conducive to the exploration of pulsed cascade laser based on the Er:YSGG crystal.

Picosecond synchronously pumped diamond Raman laser

With diamond crystals as Raman media, picosecond synchronously pumped solid-state Raman laser is theoretically studied in detail for the first time. High efficient working point and effective pulse compression working point are investigated. For both 532 nm and 1064 nm pumping, high Raman conversion efficiency can be achieved for negative cavity length detuning (∆x) and diamond crystal length of 5 mm. The higher efficiency can be obtained with longer Raman crystal, longer pumping pulse width and higher pumping power. For 532 nm pumping, effective pulse width compression can be realized for ∆x = 0 nearby and diamond crystal length of 10 mm. Shorter pulse width and higher peak power of 1st Stokes laser can be achieved with longer Raman crystal, shorter pumping pulse width and higher pumping power. The findings can contribute to the design and optimization of picosecond synchronously pumped diamond Raman lasers.

High-power wavelength-tunable and power-ratio-controllable dual-wavelength operation at 1319 nm and 1338 nm in a Q-switched Nd:YAG laser

We report the first demonstration on three types of 1.3 μm spectral region in a Q -switched Nd:YAG laser. In order to dissipate the heat deposition effectively to obtain good beam quality, the Nd:YAG rod crystal with 1° cut-angle on end faces is side-pumped by the quasi-continuous-wave pulsed laser diode. A Suprasil etalon is well designed as the intracavity mode-selector to obtain wavelength-tunable single line or power-ratio-controllable dual line operation at 1319 nm and 1338 nm. With the pump pulse width of 200 μs and pump power of 410 W, the acousto-optic Q -switched laser delivered a pulse width of 117 ns at 400 Hz repetition rate, and the M 2 factor was measured to be about 1.87. 1319 nm together with 1338 nm single-wavelength laser achieved an average output power of 47.6 W and 39.9 W with a linewidth of 0.48 nm and 0.32 nm, and a tunable range of 111.2 pm and 108.6 pm, respectively. Among dual-wavelength oscillation, both lines can be tuned at almost equal intensity level with 45.7 W total output power, which is input into an LBO crystal to generate red light of 11.4 W for 659 nm, 6.7 W for 664 nm, and 7.5 W for 669 nm. The 1.3 μm wavelength-selectable operation realized by using the same laser configuration may enhance the application in the fields of tunable lasers and THz frequency generation.

Supercontinuum and frequency comb generations in the slot SiC waveguide with four zero-dispersion wavelengths

In this paper, a slot SiC waveguide with four zero-dispersion wavelengths (ZDWs) is proposed for the supercontinuum (SC) and frequency comb generations. The four ZDWs are located at 1089, 1656, 2222, and 3113 nm, respectively. The effects of the pump wavelength, peak power, pulse width, and waveguide length on the SC generation are discussed when the waveguide is pumped near the first ZDW and the third ZDW in the anomalous dispersion region, respectively. While pumping at 1300 and 2450 nm, a near-infrared SC covering from 873 to 2444 nm and a mid-infrared SC extending from 1349 to 4727 nm with good coherences are obtained, respectively. By utilizing a 50-pulses pump source at a repetition rate of 1 GHz, we also investigate the SC-based frequency comb generation.

A large, high-gain, 400 mm single-aperture slab amplifier with 20 kJ laser output

This paper introduces a slab laser amplifier system of 400 mm single-aperture in the Integration Test Bed (ITB) laser facility. Based on the theoretical optimization model for parameters, the system uses flash-lamps with the diameter is 31 mm and the pump pulse width is 480 μs, the average small signal gain coefficient in the aperture of laser beam is 5.65%/cm. A uniformly distributed near-field output of laser can be achieved by adjusting the near-field of seed laser. The energy output reaches 20.4 kJ/4.5TW/1053 nm, the near-field modulation is 1.40:1, and the near-field contrast is 0.085.

Theoretical analyses and configuration optimizations of a LD-pumped 3.9 µm Ho:BYF laser

In this paper, we introduced the theoretical simulation results of output performances for a LD-pumped 3.9 µm Ho:BYF laser by considering two unique kinetic processes named as energy transfer up-conversion (ETU) and cross relaxation (CR). The influence of the pump energy, pump beam waist radius, pump pulse width, and crystal length on the output characteristics was discussed in detail for the Ho:BYF laser. The thermal simulation was also carried out for the Ho:BYF crystal by using a finite element method (FEM). Then, we constructed a LD-pumped experimental system and successfully realized a LD-pumped 3.9 µm laser. Next, some efforts were undertaken for optimizing the curvature radius of an output coupler (OC), focus position inside Ho:BYF bulks, and crystal length, respectively. The maximum energy of 1.87 mJ had been finally obtained after the optimization. By considering the LD-pumped solid-state laser is still rare in the mid-infrared, our study is thought to be useful for the development of a novel compact and efficient laser in the future.

Thermal lens Q-switched 1064 nm Nd:YAG laser

We report a 1064 nm Nd:YAG solid-state laser Q-switched by the dynamic thermal lens effect. The feasibility of using the thermal lens effect to realize Q-switch was proved based on the theoretical analysis of the dynamic thermal lens effect and the simulation of the Q-switched rate equation. Further, a thermal lens Q-switched experimental device with an 808 nm pumped Nd:YAG laser was constructed. The output laser beams with a repetition rate of 100 Hz, pulse width of 15.02 ns, single pulse energy of 11.9 mJ, and working wavelength of 1064 nm were realized by thermal lens Q-switch under the pump power of 412 W and pump pulse width of 80μs. The beam quality factors of the output pulse in x and y directions were 2.63 and 2.94, respectively. The results demonstrate that using a thermal lens Q-switch can generate laser beams with high energy and short pulse widths.

25.4 kW, 1.9 ns passively Q-switched 1522 nm Er:Yb:LuAl3(BO3)4 pulse microlaser at 100 Hz.

Passively Q-switched Er:Yb:LuAl3(BO3)4 pulse microlasers were investigated at a low repetition frequency of 10-200 Hz. End-pumped by a 975.6 nm quasi-continuous-wave laser diode with pump pulse width of 0.5 ms and period of 10 ms, a stable 1522 nm pulse microlaser with single pulse energy of 48.3 μJ, duration of 1.9 ns, repetition frequency of 100 Hz, peak output power of 25.4 kW and beam quality factor less than 1.2 was realized at a pump beam waist diameter of 260 μm. This eye-safe passively Q-switched pulse microlaser with high peak output power and narrow duration can be used in the portable laser rangefinder.

High-power mid-infrared pulse MgO:PPLN optical parametric oscillator pumped by linearly polarized Yb-doped all-fiber laser

We present a MgO:PPLN-based optical parametric oscillator (OPO) pumped by all-fiber Yb-doped fiber laser (YDFL). The performances of the linearly polarized YDFL are first investigated. A maximum power of 79.1 W at 1064.1 nm is obtained with the repetition rate of 300 kHz and pulse width of 200 ns. Then we examine the dependence of OPO characteristics on the pump repetition rate, pulse width, and waist diameter. By optimizing these factors, we report a maximum mid-infrared (MIR) power of 10.82 W at 3.754 µm with the conversion efficiency of 13.68%. The corresponding total output power reaches 35.4 W.

Application of the joint algorithm of smooth pseudo Wigner-Ville distribution and four-parameter particle swarm optimization to BOTDR

Short-time Fourier transform is utilized for the data processing of traditional point-frequency Brillouin optical time-domain reflectometry (BOTDR). This method can improve the measurement speed, but theoretically there is a contradiction between spatial resolution and frequency resolution. To avoid this contradiction, a joint algorithm of smooth pseudo Wigner-Ville distribution (SPWVD) and four-parameter particle swarm optimization (four-parameter PSO) algorithm is proposed to improve spatial resolution, frequency resolution and frequency shift extraction accuracy of Brillouin scattering spectrum. SPWVD can smooth the signal to enhance the frequency resolution by adding a sliding window on time and frequency domain simultaneously when making the quadratic time-frequency transforming. To further improve the fit and the extraction accuracy of the frequency shift, the Brillouin scattering spectra (BSS) processed by SPWVD are fitted to find the Brillouin frequency shift (BFS) using a four-parameter PSO algorithm that takes the gain, BFS, full width at half maximum of the BSS, and linear weight coefficients of Lorentz and Gaussian lines as unknown parameters. According to the experimental results, the BOTDR using SPWVD and four-parameter PSO joint algorithm will cost less operation time since it can get better results with fewer accumulations and it does not need to find proper initial values before curve-fitting operation. Meanwhile, the joint algorithm can improve the spatial resolution and frequency resolution over four and two times simultaneously for BOTDR with 100 ns pump pulse width.