On the basis of the GaAs photoconductor characteristic of the decrease resistance with the increase of irradiation, we first developed a high precision and ultrafast positive and negative feedback circuit. By using these techniques, we have made a novel method of mode-locking, automatic mode-selecting, Q-switching, and realizing synchronizing outputs of two independent pulse oscillators, the jitter is no more than +/- 1 ns.
A new high power laser facility with 8 beams and maximum output energy of one beam 5kJ/3.4ns/3ω has been performed and operated since 2015. Combined together the existing facilities have constructed a multifunction experimental platform including multi-pulse width of ns, ps and fs and active probing beam, which is an effective tool for Inertial Confinement Fusion (ICF) and High Energy Density (HED) researches. In addition another peculiar high power laser prototype pushes 1ω maximum output energy to 16kJ in 5ns and 17.5kJ in 20ns in flat-in-time pulse, this system is based on large aperture four-pass main amplifier architecture with 310mm×310mm output beam aperture. Meanwhile the near field and far field have good quality spanning large energy scope by use of a wide range of technologies, such as reasonable overall design technique, the integrated front end, cleanness class control, nonlinear laser propagation control, wave-front adaptive optics and precision measurement. Based on this excellent backup, 3ω damage research project is planning to be implemented. To realize the above aims, the beam expanding scheme in final transport spatial filter could be adopted considering tradeoff between the efficient utilization of 1ω output and 3ω damage threshold. Besides for deeply dissecting conversion process for beam characteristic influence of 1ω beam, WCI (Wave-front Code Image) instrument with refined structure would be used to measure optical field with simultaneous high precision amplitude and phase information, and what's more WCI can measure the 1ω, 2ω and 3ω optical field in the same time at same position, so we can analyze the 3ω beam quality evolution systematically, and ultimately to improve the 3ω limited output. In a word, we need pay attention to some aspects contents with emphasis for future huger laser facility development. The first is to focus the new technology application. The second is to solve the matching problem between 1ω beam and the 3ω beam. The last is to build the whole effective design in order to improve efficiency and cost performance.
Using di-ethoxy-silicane as precursor,a colloidal prepolymer was developed from sol-gel process.With silica colloid as modifier,the modified moisture-resistant films were prepared on neodymium-doped phosphate glass by spin coating.When the mole ratio of di-ethoxy-silicane to silica was 1∶1,the films after cure had improved abrasion-resistance.RMS was 1.245 nm,while laser-damage threshold value more than 15 J/cm~2 at the condition of 1 053 nm,1 ns.After staying in a closed circumstance at 80 ℃ and 95%RH,the films had approximately constant transmission and contact angle.It indicates that the films have a stable hydrophobic structure,good moisture-resistance,improved abrasion-resistant feature and longer service life.
High precision capacitive displacement sensor was designed.The fundamental principle and key technologies to improve the precision of sensor were introduced particularly.Following the design of modularized circuitry was conduced.Analyzing the elements that contribute to precision and stability of the sensor,complete equipotential screening technology was applied,and improved technologies applying on sine excitation circuitry,reference capacitance,polar plate and power supply were proposed.Finally,system calibration to capacitive sensor were conduced.Experimental results show that measurement range from ±5～±40 μm,resolution better than 10 nm,precision better than 20 nm can be achieved.
Aiming at high-power laser frequency conversion, we present a new scheme that can self-compensate for the thermally induced phase mismatch. The basic design of the scheme is that three crystals with the same type are cascaded, of which the crystals at both ends are used for frequency conversion and the middle crystal is used for compensating phase mismatch. By configuring the polarization states of the interacting waves in the middle crystal, the sign of the first temperature derivative of the phase mismatch is opposite to that of the frequency conversion crystals. The thermally induced phase mismatch in the first crystal can thus be self-compensated in the middle crystal. To verify the utility of the proposed scheme, we experimentally demonstrated temperature-insensitive second and third harmonic generation using KH2PO4 crystals. The results show that the temperature acceptance bandwidth is about two times larger than that of using a single crystal. Since the crystals used are of the same type, this scheme has excellent universal applicability and is almost completely free from the limitations of the laser wavelength, crystal and phase-matching type. Therefore, the scheme can be widely applied to various frequency conversion processes and is scarcely any limitations.
There is an increasing demand on the measurable velocity of laser interferometer in manufacturing technologies. The maximum measurable velocity is limited by frequency difference of laser source, optical configuration, and electronics bandwidth. An experimental setup based on free falling movement has been demonstrated to measure the maximum measurable velocity for interferometers. Measurement results show that the maximum measurable velocity is less than its theoretical value. Moreover, the effect of kinds of factors upon the measurement results is analyzed, and the results can offer a reference for industrial applications.
Thermal recovery uniformity is key factor on high energy laser device. Based on the principle of statistics, combined with the amplifier glass neodymium thermal recovery research results, we put forward degree of uniformity as evaluation index for Nd-glass laser slab on multi-segment amplifier. The simulation results show that the heat transfer coefficient of the Nd:glass laser slab on the amplifier is affected by number, pitch and diameter of the inlet jet. The heat transfer coefficient and temperature contour of Nd:glass laser slab are obtained based on numerical simulation. Moreover, the degree of uniformity of Nd-glass laser slab is on the base of simulation results. The more the degree of uniformity is close to 1, the better thermal recovery of Nd:glass laser slab.
As local defects may significantly harm beam quality and affect safe operation, a systematic analysis of the ability of a spatial filter to alleviate these adverse effects is required. Thus, the evolutional characteristics of a beam modulated by a local defect propagating through a spatial filter system at an image reply plane and a downstream plane are analyzed in detail. Modulation stripes appear at the image reply plane; these are caused by the pinhole cutoff effect. The modulation degree increases with increasing defect size. The maximum intensification factor can reach 3.2 under certain conditions. Thus, the defect size should be restricted to a reasonable size for safe operation with a specified pinhole size. Moreover, a maximal value appears at the downstream plane, and the intensity enhances with increasing defect size. To ensure beam quality, the maximum allowable defect size and angle of the spatial filter should meet special constraints. The maximum allowable defect size is calculated based on practical configuration parameters.
A new method is proposed to deduce the temporal resolution of a single-shot autocorrelator. A resolution test pattern is installed in one arm of the autocorrelator to add streaks on the beam cross section. Therefore, the autocorrelation signal is modulated when the streaked beam arrives at an autocorrelation crystal. Given the relationship between streak width and temporal delay in an autocorrelator, the temporal resolution is determined by the noncollinear angle, the streak’s width of the resolution test pattern, and the autocorrelation signal. Comparison experiments show that the proposed and conventional calibration schemes yield temporal resolutions of 65.6 and 67.8 fs/pixel, respectively, with a relative error of 3.3%. An advantage of this method is that fine temporal resolution (65.6 fs/pixel) is achievable on a short pulse (10 ps) despite the lack of a femtosecond pulse.
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