K-shell spectra of a laser-produced carbon plasma have been measured and analyzed. A graphite plate was irradiated by a 2.1ns ultraviolet laser pulse, and the radiated X-rays were measured with a flat-field grating spectrograph. The recorded lines have been identified as hydrogenic Lyman series 1s-np and heliumlike transitions 1s<sup>2</sup> -lsnp (n=2-4). The measured wavelength and the spectral resolution of the flat-field grating spectrograph were calibrated by utilizing those lines. Hydrodynamic simulations and calculations of charge-state distributions in the local thermodynamic equilibrium (LTE) regime were carried out to interpret the K-shell spectra.
We report on the recent progress on high power pulsed 2.8 μm Er<sup>3+</sup>-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 Er<sup>3+</sup>-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 Er<sup>3+</sup>-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.
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 pulsed Er<sup>3+</sup>-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.
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 10<sup>13</sup>W/cm<sup>2</sup>. 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.
SF<sub>6</sub> and C<sub>2</sub>H<sub>6</sub> are the working gas mixture of non-chain HF laser. In our work, we use a simple pumping circuit to study the influence of the electric field uniformity on the discharge characters. Three groups of electrodes with different designs have been manufactured, and different discharge characters have been got. We have analyzed the results qualitatively, and find that without preionization, uniform electric field is not the best choice to form a large volume discharge in strong negative gas such as SF<sub>6</sub>-based mixture; approximate uniform electric field may be its substitution. In such electric field the gap breakdown voltage decreases and discharge can perform much easily. The discharge channels away from the cathode surface can also diffuse together to form a large volume discharge to deposit the electric energy into the laser working gas.
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.
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/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.
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 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 SF<sub>6</sub> /C<sub>2</sub>H<sub>6</sub> 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 XeF<sub>2</sub> 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 4×10<sup>23</sup> photon s<sup>-1 </sup>cm<sup>-2</sup> 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.
A kind of beam automatic alignment method used for double paths amplification in the electron pumped excimer laser system is demonstrated. In this way, the beams from the amplifiers can be transferred along the designated direction and accordingly irradiate on the target with high stabilization and accuracy. However, owing to nonexistence of natural alignment references in excimer laser amplifiers, two cross-hairs structure is used to align the beams. Here, one crosshair put into the input beam is regarded as the near-field reference while the other put into output beam is regarded as the far-field reference. The two cross-hairs are transmitted onto Charge Coupled Devices (CCD) by image-relaying structures separately. The errors between intersection points of two cross-talk images and centroid coordinates of actual beam are recorded automatically and sent to closed loop feedback control mechanism. Negative feedback keeps running until preset accuracy is reached. On the basis of above-mentioned design, the alignment optical path is built and the software is compiled, whereafter the experiment of double paths automatic alignment in electron pumped excimer laser amplifier is carried through. Meanwhile, the related influencing factors and the alignment precision are analyzed. Experimental results indicate that the alignment system can achieve the aiming direction of automatic aligning beams in short time. The analysis shows that the accuracy of alignment system is 0.63μrad and the beam maximum restoration error is 13.75μm. Furthermore, the bigger distance between the two cross-hairs, the higher precision of the system is. Therefore, the automatic alignment system has been used in angular multiplexing excimer Main Oscillation Power Amplification (MOPA) system and can satisfy the requirement of beam alignment precision on the whole.
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 Al<sub>2</sub>O<sub>3</sub> 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.
A short pulse XeCl laser system is being developed for plasma physics and material science study. Partial spatial
incoherence seed with short pulse is amplified by MOPA chain including three discharge pumped amplifiers and two
electron beam pumped amplifiers for one beam. Final laser output of 5~10J in energy with pulse width of around 10ns
has been achieved, which lays a good foundation for full scale construction.
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.
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.
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 XeF<sub>2</sub> 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
A special designed long pulse XeCl MOPA laser system and its initial laser-target experiments are introduced. Laser produced plasmas of carbon, aluminum and copper are concerned. Based on measured results of plasma spectra and framing pictures of ejected plume, Plasma temperature and expanded speed of plasma flume are obtained.
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 XeF<sub>2</sub> 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 XeF<sub>2</sub> 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 XeF<sub>2</sub> 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<sup>-1</sup> 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.
A high power XeCl and KrF excimer lasers pumped by an intense relativistic electron beam have been developed. The pump power density ranges between 1.5 to 2.0 MW/cm<SUP>3</SUP>. The maximum output energy of 136 J with the peak power of 1.5 GW is obtained for the XeCl laser. In KrF laser case, the maximum output energy is 157 J and the peak power 2.0 GW. The UV laser interaction with some materials has been studied by this excimer laser.