Diode-pumped Laser Research Articles

Feasibility of lasing in the GaAs Reststrahlen band with HgTe multiple quantum well laser diodes

Operation of semiconductor lasers in the 20–50 µm wavelength range is hindered by strong non-radiative recombination in the interband laser diodes, and strong lattice absorption in GaAs-based quantum cascade structures. Here, we propose an electrically pumped laser diode based on multiple HgTe quantum wells with band structure engineered for Auger recombination suppression. Using a comprehensive model accounting for carrier drift and diffusion, electron and hole capture in quantum wells, Auger recombination, and heating effects, we show the feasibility of lasing at λ = 26, …, 30 µm at temperatures up to 90 K. The output power in the pulse can reach up to 8 mW for microsecond-duration pulses.

Nonlinear dynamics in intra-cavity pumped thin-disk lasers.

Cross-saturation of the gain media in intra-cavity pumped lasers leads to complex dynamics of the laser power. We present experimental results and a detailed theoretical analysis of this nonlinear dynamics for an intra-cavity pumped Yb:YAG thin-disk laser in the framework of a rate-equation model. The gain medium of this laser is residing in the resonator of a conventional, diode-pumped Yb:YAG thin-disk laser. Continuous-wave operation, periodic pulse trains, and chaotic fluctuations of the optical power of both lasers were observed. The dynamics is not driven by external perturbations but arises naturally in this laser system. Further examination revealed that these modes of operation can be controlled by the resonator length of the diode-pumped laser but that the system can also show hysteresis and multi-stability.

A Tunable Synchronous Pulsed Dual-Wavelength Laser Based on the Nd:YVO4/Nd:GdVO4 Combined Crystals Pair

A tunable pulsed dual-wavelength laser is presented based on an Nd:YVO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub> /Nd:GdVO <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sup> combined crystals pair as amplifying medium. By employing pulse width adjustment of an 808 nm laser diode pumping, and a Cr <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4+</sup> :YAG crystal for Q-switching, synchronized dual-wavelength laser pulses were obtained at 1063 nm and 1064 nm. Time jitter between the two wavelength pulses is reduced to about 10% of the laser pulse duration. Adjusting the pump beam operation parameters and tuning the crystals pair steady-state temperature between 10 °C and 50 °C, the frequency separation between the dual-wavelength laser pulses gradually decreases from 344.11 GHz to 305.99 GHz. The relative peak powers and the pulses time synchronization remain stable during their frequency separation tuning.

First tests of laser ignition in Wankel engine

Laser ignition has been studied in powerful four-stroke engines, not only because of the fast payback, but also because of the more convenient diagnostics in a large scale setup. High-performance compact engines have not been studied, even though advantages of laser ignition could be much more pronounced for those because of harmful emission reduction and multi-fuel abilities. Compact piston engines are considered as an alternative for fuel elements and batteries for portable, automotive and unmanned aerial vehicles. These are characterized by a small combustion chamber comparable to the spark plug inter-electrode gap in axial direction, and its low ratio to bore size. However, for Wankel engines this problem exists at any scale. Laser ignition of lean fuel mixtures in such engines could significantly improve performance by reduced fuel consumption, thermal loads, and a cleaner exhaust. We have investigated the possibility of laser ignition in rotary-piston (Wankel) sub-kW scale model engine using different kinds of fuel mixtures: hydrogen, methane, propane, butane, gasoline, and ethanol based. A custom built compact diode-pumped solid state laser has been used to substitute the original glow plug, respectively. Laser ignition has been found possible and quite beneficial for both types of engines and different fuel mixtures; in terms of NOx emission reduction especially.

Improving the beam quality of DPALs by refractive index gradients induced by the pump beam in the heated gain medium: experimental verification of the theoretical prediction

We recently predicted [J. Opt. Soc. Am. B 35, 558 (2018)JOBPDE0740-322410.1364/JOSAB.35.000558] that large radial gradients of the refractive index induced by the pump beam in the heated gain medium of diode-pumped alkali lasers (DPALs) could lead to improved DPAL beam quality. This effect depends on the composition of the buffer gas in the cell. We report here on verifying this counterintuitive finding by careful measurements of the beam quality factor M 2 in static Cs DPALs with different compositions of the buffer gases.

Actively Q-switched intracavity Nd:YVO4/GdVO4 Raman laser operating with multiple Raman shifts of 259, 882 and 890 cm−1

A diode-pumped acousto-optic Q-switched crystal Raman laser operating at multi-wavelength is reported, in which a c-cut Nd:YVO4 crystal was used as the self-Raman medium and a c-cut GdVO4 crystal was used as the other Raman medium. Benefited from the overlapping gain at the Raman shift of 259 cm−1 in the two crystals, the corresponding cascade Stokes light efficiently oscillated, and the 1177, 1178 nm lights corresponding to the primary Raman-shifts of the two crystals oscillated with the 1097 nm laser. The laser configuration was investigated at pulse repetition frequencies (PRFs) of 10, 20, and 30 kHz. With an incident pump power of 8.62 W, the highest average Raman laser output of 1.31 W composed of 1097, 1129, 1177 and 1178 nm lights was obtained at the PRF of 20 kHz. The 1163 nm light corresponding to the third-Stokes light of the Raman shift of 259 cm−1 only arose at the PRF of 10 kHz when the incident pump power exceeded 6.37 W.

Over 10 W linearly polarized supercontinuum directly produced in an erbium-doped fiber MOPA seeded with stretched soliton.

We experimentally achieve over 10 W linearly polarized supercontinuum (SC) generation in a polarization-maintaining (PM) erbium-doped fiber (EDF) master oscillator power-amplifier (MOPA). The house-built PM seeding EDF laser can deliver ∼209fs soliton around ∼1563.7nm, which is then stretched to >15ps using a long piece of normal-dispersion fiber. The wideband spectrum of the ultrashort seeding soliton facilitates the further spectral broadening with nonlinear effects. The soliton stretching decelerates the peak power increase, thus facilitating higher amplified average power. After several stages of pre-amplification, the stretched soliton is fed into the main amplifier constructed with PM large mode area fibers. The output average power is finally amplified to ∼11.51W. The corresponding spectrum spans from ∼1450 to ∼2200nm, indicating that SC is formed due to the induced strong nonlinear effects. The polarization extinction ratio at the output reaches over 18 dB. The PM characteristic potentially enhances the system's resistance to environmental disturbances and eliminates instabilities relating to polarization-mode coupling. Our result represents, so far, the highest SC power directly produced in an EDF MOPA, to the best of our knowledge, especially in a linearly polarized manner. This also suggests a scheme for powerful SC generation that employs direct laser diode pumping and duration-managed pulse seeding.

Спектрально-люминесцентные свойства Yb-=SUP=-3+-=/SUP=- в растворах SO-=SUB=-2-=/SUB=-Cl-=SUB=-2-=/SUB=--GaCl-=SUB=-3-=/SUB=--Yb-=SUP=-3+-=/SUP=-

The spectra of absorption, luminescence, and lifetime of Yb3+ in SO2Cl2 – GaCl3 – Yb3+ solutions were measured. Information is obtained on the Stark splitting of energy levels, absorption and stimulated emission cross sections of Yb3+. An analysis of the spectral dependence of the gain cross sections indicates that the SOCl2 – GaCl3 – Yb3 solution is promising as the active medium of a diode-pumped liquid ytterbium laser.

Watt-level visible laser in double-clad Pr3+-doped fluoride fiber pumped by a GaN diode.

We report on a red praseodymium fiber laser delivering 1.07 W at 634.5 nm with a slope efficiency of 20.7% (versus the incident pump), a laser threshold of 0.55 W, and a single-mode output (Mx,y2<1.1) in the quasi-continuous-wave regime. It is based on a 0.6 mol.% Pr3+-doped ZBLAN double-clad fiber with a 5.5 µm core, a double D-shaped (diameters, 115/125 µm) inner cladding, and a length of 5.0 m. The fiber is pumped by a multimode 443 nm GaN diode. The laser design is optimized using a numerical model. The proposed concept is suitable for the development of diode-pumped high brightness watt-level visible praseodymium fiber lasers.

Simulation and experimental results of a high-gain two-stage and double-pass off-axis Nd:YVO4 picosecond laser amplifier.

A high-gain two-stage double-pass off-axis Nd:YVO4 picosecond laser amplifier has been developed. The comprehensive influence of crystal doping concentration and pump beam quality on the small-signal gain of the Nd:YVO4 amplifier is theoretically analyzed with a model developed by considering energy transfer upconversion and pump light absorption saturation effect. The thermal effect of Nd:YVO4 crystal with different doping concentrations, undoped end cap lengths, and pump beam quality is investigated as well. Based on the theoretical analysis, a high-gain two-stage and double-pass off-axis Nd:YVO4 amplifier based on picosecond fiber seed source is realized by choosing long-composite low-doping Nd:YVO4 crystal and with high brightness laser diode pumping, delivering a gain of 28 dB and an output pulse energy of 67.5 µJ at a repetition rate of 200 kHz.

High-energy diode-pumped alexandrite amplifier development with applications in satellite-based lidar

Efficient, wavelength-tunable diode-pumped alexandrite laser systems offer the potential for a more versatile, satellite-based lidar source compared to fixed wavelength Nd:YAG systems and non-space compliant lamp-pumped alexandrite. In this paper, we develop a strategy to enable the high-energy operation required for atmospheric lidar based on an efficient diode-pumped master oscillator power amplifier (MOPA) system design. A novel multipass “diamond” slab amplifier geometry is introduced alongside the experimental results of the world’s first diode-pumped alexandrite amplifier producing a gain of 2.13 in a demonstration system. A diode-pumped Q -switched alexandrite oscillator is presented with a record-highest pulse energy of 3.80 mJ. Detailed optimization of a two-stage amplifier design is studied numerically and maximized with temperature, wavelength, and pump pulse duration to produce 50 mJ pulse energy. This forms part of an optimized alexandrite MOPA design capable of high pulse energy, showing the future potential of diode-pumped alexandrite for satellite-based atmospheric lidar.

Pump depletion in Raman lasing in a graded index multimode fibre

We examine multimode diode laser pump depletion in a graded index multimode (MM) fibre Raman laser generating a high-quality Stokes beam. Spatial ‘hole burning’ in the transmitted pump beam is demonstrated. A balance model is constructed for interaction of the pump and Stokes waves in the MM Raman laser. Analytical formulas are derived and used in calculations demonstrating qualitative agreement with experimental data. The origin of the observed quantitative discrepancies is discussed.

Detection of disbonds in adhesively bonded aluminum plates using laser-generated shear acoustic waves

Adhesively bonded metals are increasingly used in many industries. Inspecting these parts remains challenging for modern non-destructive testing techniques. Laser ultrasound (LU) has shown great potential in high-resolution imaging of carbon-reinforced composites. For metals, excitation of longitudinal waves is inefficient without surface ablation. However, shear waves can be efficiently generated in the thermo-elastic regime and used to image defects in metallic structures. Here we present a compact LU system consisting of a high repetition rate diode-pumped laser to excite shear waves and noncontact detection with a highly sensitive fiber optic Sagnac interferometer to inspect adhesively bonded aluminum plates. Multiphysics finite difference simulations are performed to optimize the measurement configuration. Damage detection is performed for a structure consisting of three aluminum plates bonded with an epoxy film. Defects are simulated by a thin Teflon film. It is shown that the proposed technique can efficiently localize defects in both adhesion layers.

Continuous-wave efficient cyan-blue Pr:YAlO$$_3$$ laser pumped by InGaN laser diode

We report on the first continuous-wave quasi three-level laser emitting in the cyan-blue spectral range in praseodymium-doped oxide materials, as we believe. Pr:YAlO $$_3$$ crystal, cooled to the cryogenic temperatures, was used as an active medium. To minimize resonator losses, the cavity mirrors were directly deposited on the crystal faces to form a microchip geometry. More than half-Watt of the output power at 493 nm wavelength with a slope efficiency of 26% has been obtained under 3 W InGaN laser diode pumping at 447 nm wavelength.

High power diode pumped solid-state femtosecond laser systems

We demonstrate high power direct diode-pumped femtosecond laser based on a commercially available configuration and pumped by multi-diode laser modules delivering high brightness and average power. The multi-diode modules employ beam-combining scheme preserving linear polarization and focusing properties of individual laser diodes. Stable passive Kerr lens modelocked (KLM) laser operation was demonstrated, producing 30 fs pulses at ∼300 mW average output power. A simple approach to numerical modelling of KLM laser operation in cases when longitudinal pump beam exhibits strong astigmatism is also discussed.

Focus on lasers, imaging, and microscopy

Focus on lasers, imaging, and microscopy

Peak-power enhancement of a cavity-dumped cesium-vapor laser by using dual longitudinal-mode oscillations.

We have performed cavity dumping of a diode-pumped alkali laser (DPAL) and have observed a saw-like structure in the pulse waveform that appears to be caused by interference between two or more longitudinal modes. We have confirmed that multimode oscillations are caused by spatial hole burning, and the largest peak was seen when only two oscillation modes were present. This phenomenon may be useful for enhancing the cavity dumping of the DPAL, but it was not always observed. Therefore, we developed a numerical simulation to predict the number of longitudinal modes excited under a given set of conditions and provides guidelines to facilitate dual-mode oscillation. Using these guidelines, we have obtained a pulse with a peak power of 250 W, which is higher than the average power circulating in the cavity and is a 38-fold enhancement of the continuous-wave (CW) output.

Low-noise high-order Raman fiber laser pumped by random lasing.

Raman fiber lasers (RFLs) have been widely utilized in long-haul optical transmission systems as pump sources for distributed Raman amplification (DRA) to increase transmission distance and capacity. However, RFLs with relatively large temporal intensity fluctuations would deteriorate signal quality due to the transfer of relative intensity noise (RIN). In this Letter, a low-noise high-order RFL common cavity pumped by an ytterbium-doped random fiber laser (YRFL) is proposed and demonstrated for the first time, to the best of our knowledge. Stable 4th-order random Raman lasing operating at 1365 nm is generated with 8.9 W of output power, without use of a multi-stage master oscillation power amplification system. Thanks to the YRFL common-cavity pumping where a wavelength division multiplexer (WDM)-assisted fiber-loop mirror is used to generate stable 1090 nm ytterbium-doped random lasing and cascaded random Raman lasing simultaneously, the RIN of the 1365 nm RFL is suppressed as low as -120dB/Hz without any peak over a 0-100 MHz span. Furthermore, the output power and lasing wavelength of this RFL can be flexibly tuned by adjusting the laser diode pump power, high-reflectivity fiber Bragg grating center wavelength, and single-mode fiber length. Hence, such a low-noise high-order RFL paves a way for the development of novel tunable RFLs with stable temporal output, leading to potential replacement of conventional RFLs for DRA in long-haul optical transmission systems to achieve better performances.

Spectral-Luminescent Properties of Yb3+ in SOCl2–GaCl3

The absorption and luminescence spectra and the excited state lifetime of Yb3+ in SOCl2–GaCl3–Yb3+ solutions are measured. Information on the Stark splitting of energy levels and on the absorption and stimulated emission cross sections of Yb3+ in SOCl2–GaCl3 is obtained. The possibility of creating a diode-pumped ytterbium laser based on SOCl2–GaCl3–Yb3+ inorganic liquid is considered.

Self-Q-switched and broad wavelength-tunable lasing in Tm3+-doped CaF2 single-crystal fiber

Self-Q-switched lasing was demonstrated for the first time around 2 μm in Thulium (Tm) doped CaF2 single-crystal fiber (SCF) using a compact linear cavity. Maximum average output power of 1.17 W was obtained under 2.38 W absorbed pump power, corresponding to the slope efficiency of up to 56.01%. Self-Q-switched laser with a 1.736 μs shortest pulse width at 48.80 kHz repetition rate was successfully realized. Besides, broad wavelength-tunable Tm:CaF2 SCF laser in 1859–2040 nm region was operated. These results show that the Tm:CaF2 SCF is a promising alternative for generating efficient micro diode-pumped pulsed lasers at 2 μm.