This paper describes the principle of non-chain pulsed HF laser, and analyzes the reason why the laser energy dropped severely with the accumulation of shots when the HF laser was in repetitive operation. In order to solve this problem, a molecular sieve absorption device was designed and mounted in the recirculation loop of the HF laser. Measurements of flow velocity indicated that the absorption device would just introduce a small decrease of flow velocity which would not influence the laser operation. Several types of molecular sieve (3A,4A,5A,13X) were used in absorbing experiments and the experiment results inferred that 3A molecular sieve was the most effective sorbent. All the experiments showed that the average drop of the output energy was not more than 5% after 1000 shots at 50Hz/20s. Compared to the energy drop of about 40% without the device, the absorption device could significantly improve the stability of the HF laser output energy and prolong the lifespan of laser medium gases.
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 large angularly multiplexed XeCl Excimer laser system is under development at the Northwest Institute of Nuclear Technology (NINT). It is designed to explore the technical issues of uniform and controllable target illumination. Short wavelength, uniform and controllable target illumination is the fundamental requirement of high energy density physics research using large laser facility. With broadband, extended light source and multi-beam overlapping techniques, rare gas halide Excimer laser facility will provide uniform target illumination theoretically. Angular multiplexing and image relay techniques are briefly reviewed and some of the limitations are examined to put it more practical. The system consists of a commercial oscillator front end, three gas discharge amplifiers, two electron beam pumped amplifiers and the optics required to relay, encode and decode the laser beam. An 18 lens array targeting optics direct and focus the laser in the vacuum target chamber. The system is operational and currently undergoing tests. The total 18 beams output energy is more than 100J and the pulse width is 7ns (FWHM), the intensities on the target will exceed 1013W/cm2. The aberration of off-axis imaging optics at main amplifier should be minimized to improve the final image quality at the target. Automatic computer controlled alignment of the whole system is vital to efficiency and stability of the laser system, an array of automatic alignment model is under test and will be incorporated in the system soon.
A 3A molecular sieve separation device was designed and mounted in a closed-cycled non-chain HF laser to separate the ground state molecule being produced in discharge region from gas stream in order to improve the stability of laser output energy. Experiments were carried out with several different discharge voltages and gas flow velocities, and the preliminary results show that the molecular sieve separation device could dramatically decrease the decay of output energy of HF laser while improving the laser energy stability.
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.
The design and performance of a closed cycle, repetitively pulsed HF/DF laser is described. For obtained higher stable laser pulse energy and running frequency, discharge stability with different electrode profile and different gas circulation structure are researched. The functional relations of laser pulse energy with electric field strength (E) and gas mixture pressure (P) for various gas flow velocity are studied. It is shown that with preliminary optimized of the gas injection segment structure before pump region and optimal E/P conditions, maximal running frequency of 100Hz is obtained and operating stability keeps well. Under these conditions, the laser average power is 40W and peak power is 4MW.
Excimer laser has been shown to be efficient tools in plasma physics and material science. Recent progress on techniques of beam control in excimer laser system required for energy scaling are overviewed, Configuration and initial results of a 100J/10ns, 18 beam excimer laser system are given.
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.
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.
Surface discharge Radiation Source has been used as optical pumping source of XeF(C-A) gaseous laser. In
previous works, discharge deposition power, transition efficiency and UV radiation intensity of surface discharge
Radiation Source were mostly concerned, but the jitter of repetitively pulsed surface discharge was little studied. An
optical pumping source by segmented surface discharge on Al2O3 ceramic substrate is developed to design stable
XeF(C-A) laser with pulse repetitive mode. Distorted electric field near the surfaces of the ceramic substrate is calculated
based on equivalent chain circuit model under conditions of charging voltage from 0 to 26.8kV, thickness of the substrate
from 1mm to 3mm, and trigger pulse voltage from 47kV to 63kV. Analysis about trigger characteristics of pumping
source is carried out, and influence of these conditions on discharge jitter is discussed. And discharge jitter is investigated
in detail under different conditions. The experimental results show that discharge jitter decreases with increasing
charging voltage and trigger pulse voltage, as well as decreasing thickness of ceramic substrate, and the pulse repetition
rate has little influence on the discharge jitter in the range of 1Hz to 30Hz. These experimental results are coincident with
numerical simulation results. Normally, the discharge jitter can be less than 30ns. Research results indicate that the
optical pumping source has good time stability of repetitive pulse discharge.
The experimental setup and performance of a non-chain transverse excited HF laser with UV pre-ionization is described.
Electric discharge characteristics in gas mixture of SF6 /C2H6 are investigated for various initial conditions by recording
the discharge plasma fluorescence intensity and temporal evolution of discharge current and voltage. The laser pulse
energy is studied in different charging voltage, gas mixture pressure and concentration. It is shown that the process of
discharge in gas mixture has three phases: glow discharge, voltage plateau and arc discharge. The optimal energy
deposition obtained at the critical point that the voltage plateau just disappears. Maximal output energy of 0.6J and
electrical efficiency of 2.5% are obtained.
The method of the spectral narrowing of optically pumped XeF(C-A) laser is discussed. Two experimental schemes are
used to narrow the spectrum of XeF(C-A) laser. Linewidth less than 1 nm can be obtained normally and the minimum
linewidth is up to 0.2 nm with more than 2J output energy. Broadband tunability of the XeF(C-A) laser in the spectral
range from 448 to 520nm is accomplished. The results of spectral narrowing of XeF(C-A) laser with different
experimental schemes are compared and tunable spectra of the XeF(C-A) laser are given.
In this paper, a surface discharge optical pumping source module with high repetition mode is described. The electrical
and radiative properties of the optical pumping source have been studied. The equivalent resistance and inductance, the
maximum current and the deposition efficiency of the discharge circuit under various distances of electrodes have been
compared. The framing photographs of XeF2 photodissociation wave have been obtained which show the XeF laser can
be formed under the experimental condition. The repetition characteristics of the optical pumping source have been
experimentally studied. The maximum pulse repetition rate is up to 90 Hz. The ablation of the dielectric material surface
The development of XeF(C-A) lasers by optical pumping in Northwest Institute of Nuclear Technology during recent 10 years is described in this paper. A joule level of XeF(C-A) laser optically pumped by a sectioned surface discharge was studied with the total efficiency of 0.1%. A more efficient XeF(C-A) laser was developed with the maximum outpup energy of 18.6 joules by two-side optically pumping and repetition mode operating.
Taking advantage of the framing camera, the performances of the laser pumping source were studied. The framing
photographs of XeF2 photodissociation wave (PDW) under different experimental conditions had been taken, which
showed the forming process of the PDW. The variations of the radius, thickness and developing velocity of the PDW
with time had been obtained under different XeF2 initial concentrations. The temporal and spatial characteristics of the
PDW had been analyzed. The irradiative intensity of pumping source could be diagnosed by calculating the time
evolution of XeF2 photodissociation wave which was photographed by framing camera. The framing photographs of the
discharge plasma channel under different conditions had been obtained. The effect of the discharge plasma extension on
the efficiency resistance of the discharge circuit had been analyzed.
A 250 J/210 ns four-stage XeCl laser system named Photons has been developed. Five lasers in MOPA chains characterized by different pumping techniques are described. Also, the main experimental results of the Photons are given.
A four-stage XeCl laser system named Photons has been developed for studying laser interaction with materials. The Photons are outlined and preliminary results characterizing the system are given. The master oscillator Photon-1 can provide “seed” light with laser energy of about 40mJ, pulse duration of about 250ns and good beam quality of nearly diffraction-limited divergence angle and narrow line width less than 1 cm-1 for whole system. The output energy of laser system of 251J has been obtained by four-stage amplification. The synchronization among five lasers is realized by the combination of low voltage timer, high voltage synchronic generators and compensated cables. The demonstration shows Photons good operation with low jitter of less than ±20ns.