The square pulse output of Linear transformer driver (LTD) is of great interest for excimer lasers, where the efficiency can be greatly improved in this way. The design of square pulse output LTD within the single cavity was presented, then the influence of jitter and loop inductance on square pulse output was studied, it can be found that the higher the value of the jitter and loop inductance, the more the risetime of the voltage pulse, which hinders the shaping of the square pulse output. Then the method to change the square pulse width by varying the triggering times was presented, through the simulation, it is found that when the triggering interval is set to 15s, the square pulse characteristics of the voltage output are more obvious, the flat top is flat, and the pulse width is wider. The bricks within the single cavity can be designed by two methods, where the one is using the same sized capacitors, the other is using the different sized capacitors to synthesize a flat voltage pulse, the choice of the two methods should be based on the cost and requirements of the excimer laser, including the amplitude of the output voltage, the pulse width and the laser beam quality. The reference of designing the square pulse LTD can be provided by this paper
In the high-power laser device, through precisely positioning the target and pointing multiple laser beams at a very small area on the target surface, the laser power density coupled with the target can be greatly improved and is conducive to the research of laser-induced plasma experiments. This paper proposes a set of target positioning and laser beam pointing system, which has advantages of high experiment efficiency, high target positioning and laser pointing accuracy. This system can automatically correct the attitude and position of targets, and make all laser converge together by adjusting their incident directions. It was verified that the target positioning error is 14.83 µm and the beam guidance accuracy is 9.70 µm.
Excimer lasers driven by linear transform driver (LTD) are expected to be used in inertial confinement fusion (ICF). The main problem of LTD in excimer lasers is synchronous triggering on multiple circuits, gas spark switches are important for synchronous triggering, which are required to be fired with low prefire probability and jitter. Multi-gap switch, as a kind of the gas spark switches, is always used in LTD. In this paper, a comparison study of corona discharge current of a multi-gap switch for LTD from the aspects of self-breakdown voltage and jitter is presented. The length of equalizing voltage needle was optimized by the electrical strength simulation. Using the optimized needle, the corona currents of the two gaps were measured, then it was found that the corona currents differ when the lengths of the corona needles were equal. To study if the difference of current in each gap affects the breakdown voltage and jitter of the switch, the length of the needle was adjusted to make the corona current the same. Then the breakdown voltage and jitter were measured under the two conditions of equal and unequal corona currents. It can be found that smaller the difference of current in each gap, higher the breakdown voltage and lower the jitter of the switch. It can be concluded that the corona needle can be adjusted to make corona current of each gap equal, which can be beneficial to increase the breakdown voltage and lower the jitter of the switch.
We present a narrow linewidth frequency-doubled Cr:LiSAF laser with a 450- to 460-nm tunability and maximum repetition frequency (RF) of 63 kHz. Under a pump power of ∼900 mW, the fundamental wavelength could be tuned at the range of 883 to 1020 nm, with a maximum output power of 180 mW at 910 nm. The pulsed operation was achieved by using an acousto-optical modulator. An LBO crystal was adopted for intra-cavity frequency doubling and a maximum output power of 44.8 mW was obtained at 455 nm, indicating a slope efficiency of 11.2%. The spectral linewidth was <0.1 nm in the whole tuning range.
A theoretical model based on rate equations for actively Q-switched Er3+-doped ZBLAN fiber laser is built. The operation behaviors and output characteristics of the actively Q-switched fiber laser at 2.8 μm are analyzed. Effects of some important laser parameters, such as pump power levels, reflectivity of the laser output coupler, fiber lengths, Er concentrations, etc., on laser output were investigated. The model and simulating results are useful for design and optimization of actively Q-switched fiber laser at 2.8-μm region.
We report a continuous wave (CW) all-solid-state Cr:LiSAF laser with a prism-controlled coupled-cavity. Broad-band tuning of 198 nm from 784 nm to 982 nm is demonstrated. The output power is always above 14 mW tuned from 825 nm to 975 nm and reaches the maximum value of 21.4 mW at 900 nm. Dual-wavelength operation is observed at the edge of the tuning range. The coupled-cavity passive loss is discussed and calculated to be 18%.
We report on the recent progress on high power pulsed 2.8 μm Er3+-doped ZBLAN fiber laser through techniques of passively and actively Q-switching in our research group. In passively Q-switched operation, a diode-cladding-pumped mid-infrared passively Q-switched Er3+-doped ZBLAN fiber laser with an average output power of watt-level based on a semiconductor saturable absorber mirror (SESAM) was demonstrated. Stable pulse train was produced at a slope efficient of 17.8% with respect to launched pump power. The maximum average power of 1.01 W at a repetition rate of 146.3 kHz was achieved with a corresponding pulse energy of 6.9 μJ. The maximum peak power was calculated to be 21.9 W. In actively Q-switched operation, a diode-pumped actively Q-switched Er3+-doped ZBLAN fiber laser at 2.8 μm with an optical chopper was reported. The maximum laser pulse energy of up to 130 μJ and a pulse width of 127.3 ns at a repetition rate of 10 kHz with an operating wavelength of 2.78 μm was obtained, yielding the maximum peak power of exceeding 1.1 kW.
A pulsed Er3+-doped ZBLAN fiber laser at 2.8 μm in fundamental-transverse-mode operation is reported. Stable gainswitching
is achieved with the repetition rate range from 0.5 to 10 kHz. The maximum laser pulse energy of up to 4.2 μJ
and pulse duration of 1.18 μs at a repetition rate of 10 kHz, yielding the maximum peak power of 3.5 W, has been
obtained. The maximum slope efficiency with respect to the launched pump power at 975 nm is determined to be 12.2%.
Pulse spikes occur by increasing the pump energy of larger than 75 μJ.
The investigations of the XeF laser bumped by ultraviolet radiation have been studied for more than 20 years in Northwest Institute of Nuclear Technology (NINT Xi’an China). Up to now, several XeF laser devices were developed and an integrative experimental system has been set up which is comprised of a laser device, an electrical power supply, a high voltage trigger generator and a mixture gas supply device. Many key technologies were studied in detail and have been applied now. These technologies include section surface discharge, XeF2 photodissociation, synchronal trigger generating, double-sides optical pumping from opposite directions, active mixture gases supplying in real time, gases circulation, and so on. The XeF laser system operating on pulse repetition frequency (PRF) is up to 10 Hz. Two kinds of operating modes were applied. For the open gas flowing mode, the pulse energy of 3.2 J and the average power of 32 W at 10Hz is obtained. For the gases circumrotate mode, the average energy of 20 laser pulses is more than 0.5J.
A general model has been developed for the optimization of the end-pumped solid-state lasers by including the effect of beam quality of the pump, and ellipticity of pump and oscillation beam into the overlap integrals. Previous models of mode-matching between oscillation and pump beam just consider of the ellipticity of pump beam, and assume the Gaussian oscillation beam to be circle TEM00 mode. Our model of mode-matching considers not only the ellipticity of the pump and oscillation beam, but also the angle of the long axis of the pump and oscillation beam. To illustrate the utility of the present model, an end-pumped Cr:LiSAF laser pumped is considered and the experimental results fit well with the theoretical results.
This paper describes systematically the properties of the surface discharge pumping source. The pre-ionization technology was investigated. The characteristics of the surface discharge and the photodissociation wave of exciting media have been studied. The temporal and Spatial Stability of discharge were measured and analyzed. The discharge spectral and ablation rate of three different materials were obtained.
We present the development of a laser damage and ablation test-bench able to accommodate ultrashort pulses down to 10
fs pulse duration. The laser test-bench is operated in air and we demonstrate its capability to accurately measure the
damage and ablation characteristics of optical materials, like fused silica, irradiated by single ultrashort pulses of < 15 fs
pulse duration. The careful characterization of beam propagation allows us to ascertain the precise retrieval of laserinduced
damage and ablation threshold fluences as well as to identify the energetic regime yielding to beam
filamentation.
The metrology of laser damage is essential for the development of intense laser chains and their applications, especially
in micromachining. We first present a test bench able to accurately measure the damage and ablation behaviour of
optical materials and components irradiated by femtosecond lasers (< 15 fs - 5 ps). We further illustrate the interest of
our measurements through examples related to laser technology and engineering, and also fundamental knowledge of
laser-matter interaction.
High power acoustic sources, generated by laser-induced breakdown when high power laser is focused into water, have extensive application prospects in laser medicine and ocean exploration. Combining the models of sound column and plasma disc in laser-induced breakdown generated sound field, a plasma cylinder model is established. The directivity of the sound field, and it’s characteristics are mapped and analyzed through numerical simulation, as well as theoretical analysis. An experiment is designed and performed to verify the plasma cylinder model. The experimental results, which are in a good agreement with the simulation, reveal the maximum pressure amplitude of the acoustic signals is at the direction vertical to the light propagation, and present a distinct major-lobe and minor-lobes.
The design and performance of a closed cycle, repetitively pulsed HF laser is described. The homogeneous glow discharge is formed with UV pre-ionization and transverse discharge structure. The optimal output parameters of single pulse operation are given by the investigation of discharge characteristics in SF6 /C2H6 gas mixture and output characteristics of laser pulse. The repetitively pulse energy stability of laser device are checked with different conditions of gas flowing velocity, charging voltage and total pressure of gas mixture. It is shown that the maximal output energy of laser pulse of 0.6J, peak power 3MW are obtained. Total efficiency of laser device is about 2.4%. When the gas mixture circulating with 4m/s flowing velocity, the maximal running frequency of 50Hz are obtained and operating stability keep well. Under these conditions, the laser pulse energy keeps stable and the average output power is 18W.
The theoretical analysis and experimental research of the optical parametric oscillator (OPO) based on periodically poled LiNbO3 (PPLN) crystal are presented. The wavelength tuning curves of PPLN-OPO are calculated through the coupling equations of the three-wave mixing. An optical parametric oscillator with the output signal at 1.49μm and idler at 3.8μm, which is pumped by a Nd:YAG laser at 1.064μm, is obtained based on PPLN of length 20mm and thickness 0.5mm. When the pump power of the Nd:YAG laser is 5.2W with a repetition rate of 5kHz, the output of the idler at 3.8μm reaches 307mW.
This paper presents the results of studies on high power photochemical XeF(C-A) laser with repetition mode. A new design of optical pumping source is proposed and the deposition efficiency is higher than 75 %. The form process and the temporal and spatial characteristics of the XeF2 photodissociation wave are studied experimentally. The results indicate that when the deposition power is 12.5 MW/cm, the maximum brightness temperature reaches more than 25 kK and the photon flux obtained more than 4×1023 photon s-1 cm-2 in the VUV range of 130 nm~180 nm. A novel XeF(C-A) laser which can be operated in repetition mode has been developed based on surface discharge optical pumping technique. The ideal output energy results of 20 laser pulses are presented under different repetitive rates and their optimal experimental conditions. Output energies of more than 4J and better stability can be obtained when the laser device operates at 1, 2 and 5 Hz, respectively. When the gas feed rate is larger than 53L/s, the average energy of 20 laser pulses is up to 3.2J at the repetitive rate of 10Hz. The technology for the laser spectral narrowing is studied.
The output energy stability of discharged-pumped pulsed HF laser in repetition rate mode is
studied experimentally, and the optimal operating conditions are obtained. The experimental
results show that the output energy decreases quickly with the increase of repetition rate, and
increasing gas flow rate is beneficial to improve the discharge stability and the output energy
stability as well. By optimizing the operating conditions, the laser can operate stably at the
repetition rate of 50 Hz, with the stable output energy of about 260 mJ, and the average power is
about 13 W.
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