Diode-pumped Solid-state Laser System Research Articles

Fabrication of micron-sized protrusions on metal surface for metal/polymer easy-disassembly joining by selective laser melting technology

Artificial protrusions fabricated on metal surfaces are adequate for the mechanical interlocking to strengthen the metal/polymer joint. The morphology and its adhesion with the metal substrate of the fabricated protrusions greatly influence the joint strength and joint detachability. However, the large-sized protrusion can cause carbon fiber damage when embedded into the polymer plate, which results in the decline of the joint strength. This paper applied a diode-pumped solid-state laser system to melt stainless powders to fabricate micron-sized protrusions on metal surfaces. The effect of four impacting factors, original powder size, powder bedding thickness, laser power density, and laser irradiation time, on the formation of micro-protrusions was investigated. SEM was used to characterize the morphology and diameter of the formed micro-protrusions. The results showed that the fabricated micro-protrusions present a spherical shape under the stable manufacturing process, and the diameter ranged from 100 µm to 500 µm. The micro-protrusions size positively correlated with the original powder size and powder bedding thickness. Laser power density directly affected the forming of micro-protrusions, and the suitable process window was between 160 W/mm2 to 290 W/mm2. When the laser irradiation time was 10 s, it helped stabilize the fabrication process.

SBS pulse compression using bulk fused silica by diode-pumped solid-state lasers at 1 kHz repetition rate

This study is focused on constructing a highly stable diode-pumped solid-state laser system by conducting experiments on high-repetition-rate SBS pulse compression using bulk fused silica. A multi-rod serial-connection structure is adopted for SBS expriments by comparing K8 glass and fused silica medium at a 10 Hz repetition rate. The optimized structure is obtained according to variation of the pump power density. Based on the optimized structure, fused silica-based SBS pulse compression is carried out in the range of 100–1000 Hz and the parameter performance of laser system after compression is also evaluated by comparing a HT270 liquid medium. Experimental results indicate that the energy efficiency of fused silica-based SBS is improved by approximately 40% compared with that of K8 glass. Further, the energy relative standard deviation of fused silica-based SBS is reduced by approximately 88% compared with HT270 medium, indicating that bulk fused silica is advantageous for high-repetition-rate SBS pulse compression because of its un-fluidity, high thermal conductivity and power-load ability. In addition, a 1 kHz highly-stable sub-nanosecond compressed pulse is achieved using bulk fused silica medium at a pump energy of 50 mJ. Furthermore, the SBS energy efficiency can be further improved by increasing the input energy.

Hydroxyl radical planar imaging in flames using femtosecond laser pulses

Hydroxyl radical (OH) planar laser-induced fluorescence (PLIF) imaging is one of the most widely used laser diagnostic techniques to investigate reacting flows such as flames and plasmas. In conventional PLIF experiments, 10-Hz, commercial Nd:YAG/dye-laser-based systems are often used for OH excitation. In recent years, significant developments are also reported in using diode-pumped solid-state and pulse-burst laser systems for high-repetition-rate (kHz–MHz) measurements. In general, all these laser sources generate nanosecond-duration, narrowband laser pulses which are to be tuned to a specific ro-vibrational excitation transition line. In the present work, we investigate the use of broadband, ultrashort femtosecond-duration (fs) laser pulses for OH-PLIF imaging in flames. The fs excitation of the OH A2Ʃ+ ← X2∏ (1, 0) transition is followed by fluorescence detection from the (0, 0) and (1, 1) vibrational bands. Because of the broad bandwidth, the excitation laser is coupled to a large number of OH ro-vibrational transitions at the same time; hence, species selectivity is obtained by detecting fluorescence emission in the 310–325 nm spectral window. This scheme is shown to be free from fluorescence from other flame species as confirmed by high-resolution fluorescence spectra recorded under a variety of flame conditions. Measured OH number density profiles in CH4, C2H4 and H2 calibration flames are in good agreement with model predictions. Two-dimensional imaging of OH at 1-kHz repetition rate is also demonstrated in a turbulent diffusion flame. The present fs OH-PLIF scheme can find novel applications in fundamental chemical physics research, as well as in practical engine combustion and flame diagnostics.

Influence of pump-beam parameters and crystal optical properties on propagation of thermally affected Bessel–Gaussian beams generated by a solid-state laser

In diode-pumped solid-state laser system, the generation and propagation of Helmholtz–Gaussian beam families such as Bessel–Gaussian (BG) beam can dramatically suffer from the effects of heat load. In this study, based on the ABCD matrix for BG beams passing through a graded-index medium, expressions for the thermal lens focal length and the output beam are obtained. Furthermore, to evaluate the impact of the pump-beam parameters and crystal optical properties, the intensity distribution of the zeroth- and first-order BG beams against radial distance together with its corresponding transverse intensity pattern on X–Y plane under different pump powers, pump beam waists, absorption coefficients, and thermal conductivities are simulated and compared. The simulation results indicate that for powerful narrow pump beam, the thermal-induced effects are so dramatic that the intensity profiles are altered, as the discernment of BG beams is not easily feasible; however, taking into account the large pump waist, high thermal conductivity and small absorption coefficient can partly cause the laser output similar to non-thermal one despite high pumping power is received. Therefore, the precise selection of laser parameters can considerably reduce the effects of induced heat on the generation and propagation of BG beams. The obtained results are a valuable hint to experimenters for beam identification and beam quality monitoring.

Semiconductor diode laser device adjuvanting intradermal vaccine

A brief exposure of skin to a low-power, non-tissue damaging laser light has been demonstrated to augment immune responses to intradermal vaccination. Both preclinical and clinical studies show that this approach is simple, effective, safe and well tolerated compared to standard chemical or biological adjuvants. Until now, these laser exposures have been performed using a diode-pumped solid-state laser (DPSSL) devices, which are expensive and require labor-intensive maintenance and special training. Development of an inexpensive, easy-to-use and small device would form an important step in translating this technology toward clinical application.Here we report that we have established a handheld, near-infrared (NIR) laser device using semiconductor diodes emitting either 1061, 1258, or 1301nm light that costs less than $4000, and that this device replicates the adjuvant effect of a DPSSL system in a mouse model of influenza vaccination. Our results also indicate that a broader range of NIR laser wavelengths possess the ability to enhance vaccine immune responses, allowing engineering options for the device design.This small, low-cost device establishes the feasibility of using a laser adjuvant approach for mass-vaccination programs in a clinical setting, opens the door for broader testing of this technology with a variety of vaccines and forms the foundation for development of devices ready for use in the clinic.

DPSSL pumped 20-TW Ti:sapphire laser system for DD fusion experiment

A diode-pumped solid-state laser (DPSSL) pumped 20-TW output Ti:sapphire laser system has been developed. A diode-pumped Nd:glass laser with output energy of 12.7 J in 527 nm was used as a pump source for a 20-TW Ti:sapphire amplifier. A CeLiB6O10 nonlinear optical crystal was used as a frequency doubler of the Nd:glass DPSSL[1]. Figure 1 shows typical output pulse energy of the 20-TW amplifier as a function of pumping energy and a near field pattern. A 1.65 J pulse energy was obtained by 4.5 J pump energy. The amplified seed pulse is compressed to typically 60 fs as shown in Fig. 1 by a vacuumed pulse compressor with 80% of transmissivity. Encircled energy ratio, into a circled with 8 μm diameter area, of far field pattern focused by off-axis parabolic mirror with F# of 3 is numerically evaluated to 40% at TW class output condition. Then focal intensity would reach to 1018W/cm2. This all- DPSSL system contributes for stable and continual investigation of laser induced plasma experiment. We have succeeded continual and high efficient generation of DD fusion neutron from CD nano-particles by cluster fusion scheme using the 20-TW laser. A yield of ∼105 neutrons per shot was stably observed during continuous 100 shots with repetition rate of 0.1Hz.

The all-diode-pumped laser system POLARIS – an experimentalist’s tool generating ultra-high contrast pulses with high energy

Abstract The development, the underlying technology and the current status of the fully diode-pumped solid-state laser system POLARIS is reviewed. Currently, the POLARIS system delivers 4 J energy, 144 fs long laser pulses with an ultra-high temporal contrast of $\def \xmlpi #1{}\def \mathsfbi #1{\boldsymbol {\mathsf {#1}}}\let \le =\leqslant \let \leq =\leqslant \let \ge =\geqslant \let \geq =\geqslant \def \Pr {\mathit {Pr}}\def \Fr {\mathit {Fr}}\def \Rey {\mathit {Re}}5\times 10^{12}$ for the ASE, which is achieved using a so-called double chirped-pulse amplification scheme and cross-polarized wave generation pulse cleaning. By tightly focusing, the peak intensity exceeds $3.5\times 10^{20}\ \mathrm{W\ cm}^{-2}$ . These parameters predestine POLARIS as a scientific tool well suited for sophisticated experiments, as exemplified by presenting measurements of accelerated proton energies. Recently, an additional amplifier has been added to the laser chain. In the ramp-up phase, pulses from this amplifier are not yet compressed and have not yet reached the anticipated energy. Nevertheless, an output energy of $16.6\ \mathrm{J}$ has been achieved so far.

Overview of the HiLASE project: high average power pulsed DPSSL systems for research and industry

Abstract An overview of the Czech national R&D project HiLASE (High average power pulsed laser) is presented. The project focuses on the development of advanced high repetition rate, diode pumped solid state laser (DPSSL) systems with energies in the range from mJ to 100 J and repetition rates in the range from 10 Hz to 100 kHz. Some applications of these lasers in research and hi-tech industry are also presented.

High power continuous-wave 1064 nm DPSS laser for machining semiconductor and metal materials

A diode-pumped solid-state (DPSSL) laser system with 808 nm laser as pump source has been developed successfully. We used the optically anisotropic crystal Nd:YVO4 as the active medium. The threshold pump power and slope efficiency were measured and discussed. With lowly doped crystal Nd:YVO4 0.27% and concave-plane cavity, the laser showed good performance in the pumping range up to 11 W. Using the 1064 nm beam, micromachining were successfully conducted upon some normal materials such as plastic, wood; some semiconductors such as silicon and metals such as aluminum, copper, steel.

Status of HiLASE project: High average power pulsed DPSSL systems for research and industry

We introduce the Czech national R&D project HiLASE which focuses on strategic development of advanced high-repetition rate, diode pumped solid state laser (DPSSL) systems that may find use in research, high-tech industry and in the future European large-scale facilities such as HiPER and ELI. Within HiLASE we explore two major concepts: thin-disk and cryogenically cooled multislab amplifiers capable of delivering average output powers above 1kW level in picosecond-to-nanosecond pulsed regime. In particular, we have started a programme of technology development to demonstrate the scalability of multislab concept up to the kJ level at repetition rate of 1-10Hz. Diode pumping of solid state laser materials in general improves the stability and efficiency of solid state lasers in comparison to flash-lamp pumped laser sources. The main reason for this improvement is the fact that the rather small bandwidth emission of highly efficient semiconductor laser diodes can be perfectly matched to the absorption band of solid state laser materials. The laser is therefore pumped only with the necessary radiation. The laser materials under consideration for HiLASE show furthermore a small Stokes-shift between the absorption and lasing transitions. The two mentioned facts lead to a much smaller heat deposition in the active laser material in DPSSL in comparison to conventional flash-lamp pumping of active materials. The reduced heat deposition, stability and maturity of laser diodes as well as their over the years reduced prices allow nowadays to consider to work on the development of solid state pulsed laser sources entering and exceeding average power ranges in the order of 1-10kW.

Study on propagation features of a Gaussian probe beam in a multiple lens-like rod system

In this paper, the propagation characteristics of a perfect Gaussian probe beam are studied for a diode-pumped solid-state laser (DPSSL) system. By using the algorithm based on the complex self-consistency analyses, the beam parameters can be evaluated if the radius of curvature and the spot size of the wavefront at the incident surface of the laser media are known beforehand. The birefringence in a tandem-set rod configuration is also investigated for a Gaussian Ne-He beam and the tendency of depolarization variations is in agreement with the previous prediction in principle. It has also been found that the deviations between the experimental data and the theoretical results are not merely resulting from the plane-wave approximation in the previous studies. Further researches are needed to give a reasonable explanation.

Development and application investigation of an ICSHG 532 nm diode-pumped solid-state laser system

A diode-pump solid-state laser system emitting a 532 nm beam has been developed. The pump source is an 808 nm diode laser, which has gained wide acceptance in research as well as in commercial production due to its effectiveness and reasonable price. The active medium was chosen to be Nd:YVO 4 (neodymium-doped yttrium orthovanadate), a material with many advantages over traditional Nd:YAG (neodymium-doped yttrium aluminum garnet) such as a low lasing threshold and linearly polarized beam. However, the thermal conductivity of Nd:YVO 4 is not as good as Nd:YAG, thus the thermal lens effect inside Nd:YVO 4 under high pumping intensity becomes severe and detrimental to the laser performance. Our work showed that careful adjustments of Nd:YVO 4 temperature as well as of the cavity's parameters played an important role in the performance of the laser. Potassium titanyl phosphate (KTP), a nonlinear optics crystal, was used to convert the fundamental 1064 nm laser radiation from Nd:YVO 4 into 532 nm. The 532 nm laser beam has been successfully proven to cut wood, plastic and aluminum.

A Laser Technology Test Facility for Laser Inertial Fusion Energy (LIFE)

A LIFE laser driver needs to be designed and operated which meets the rigorous requirements of the NIF laser system while operating at high average power, and operate for a lifetime of >30 years. Ignition on NIF will serve to demonstrate laser driver functionality, operation of the Mercury laser system at LLNL demonstrates the ability of a diode-pumped solid-state laser to run at high average power, but the operational lifetime >30 yrs remains to be proven. A Laser Technology test Facility (LTF) has been designed to specifically address this issue. The LTF is a 100-Hz diode-pumped solid-state laser system intended for accelerated testing of the diodes, gain media, optics, frequency converters and final optics, providing system statistics for billion shot class tests. These statistics will be utilized for material and technology development as well as economic and reliability models for LIFE laser drivers.

Temporal pulse control of a multi-10 TW diode-pumped Yb:Glass laser

At the Institute of Optics and Quantum Electronics in Jena, Germany, the currently most powerful diode-pumped solid-state laser system with 25-TW peak power Polaris is in operation. In this paper we give an overview about the dispersion management of the chirped pulse amplification in order to minimize the pulse duration and thus to maximize the intensity available for experiments. A detailed description of the stretcher and compressor design with a novel alignment routine is given as well as measurements for the pulse duration and the temporal contrast. The far field measurement of the beam focussed by an off-axis parabola yields a nearly diffraction limited focal spot.

Diode-pumped lasers for ultra-high peak power

The generation of the highest laser peak intensities at a high degree of system compactness can be achieved by combining modern diode-pump technologies with the chirped pulse amplification technique. In principle, the spectroscopic properties of the gain medium determine the scaling laws of both high output pulse energy and short pulse duration. Here we introduce a novel criterion classifying laser materials with respect to their ability to generate pulses of highest peak power in a diode-pumped solid state laser system. Furthermore, amplified spontaneous emission as well as laser damage issues affecting the efficiency and compactness of a laser amplifier system are discussed.

Efficient compact watt-level deep-ultraviolet laser generated from a multi-kHz Q-switched diode-pumped solid-state laser system

Stable high-power operation in the deep ultraviolet is achieved from a multi-kHz diode-pumped multi-longitudinal-mode Q-switched Nd:YAG laser by fourth harmonic generation in an external resonant cavity and by fifth harmonic generation using sum-frequency mixing of the fourth harmonic and the residual fundamental in a β-BBO crystal. Over 2.1 W of 266 nm radiation and 540 mW of 213 nm radiation were generated from a fundamental power of 7 W of 1064 nm light at 5 kHz. The overall conversion efficiency from IR to deep ultraviolet at 213 nm is larger than 7.5%.

Theory and optimization of lens ducts

Lens ducts are simple optical devices that have found application in the coupling of pump radiation from extended two-dimensional semiconductor laser diode arrays into solid-state laser gain media. The operation of these devices relies on the combined effects of lensing at their curved input surface and channeling by total internal reflection off their canted planar sides, to contain and couple semiconductor diode laser light efficiently to the input face of a solid-state laser crystal or glass. The lens duct provides a robust method for amplifying the irradiance of laser diode array pump sources and has made possible a scalable diode end-pumping architecture that offers the opportunity to expand significantly the number of ions and transitions that can be practically engaged in diode-pumped solid-state laser systems. An analytic model that describes the transfer efficiency of lens ducts and aids in the optimization of their design is presented.

Photorefractive two-wave mixing in GaAs using a diode-pumped Nd:YLF laser at 1.31 μm

Two-wave mixing has been observed in Cr-doped semi-insulating GaAs using a compact Nd:YLF diode-pumped solid-state CW laser system at 1.31 μm. Significant enhancement of the two-wave mixing gain was achieved through application of AC electric fields.