We proposed a self-referenced technique for measuring the spatiotemporal characteristics of ultrashort pulses using the coherent diffraction imaging. This technique includes the wavelength spatial multiplexing coherent diffraction imaging measurement and the three-dimensional spatiotemporal amplitude and phase reconstruction. In experiment, we verified the feasibility of this technique by measuring a pulse from the femtosecond laser oscillator. Wavelength spatial multiplexing was realized by the combination of two-dimensional diffracted optical element and narrow-band-pass filter, and the amplitude and phase information of each wavelength was recovered by ePIE (extended Ptychographic Iterative Engine) algorithm. This technique can measure the three-dimensional spatiotemporal amplitude and phase information of ultrashort pulses with high resolution and simplicity. In the future, it is expected to be an effective method for the comprehensive monitoring of the spatiotemporal optical field of ultrashort pulse lasers, and will be helpful for the laser performance improvement.
We proposed a single-shot diagnostic for spatiotemporal laser-plasma evolution by the multi-dimensional encoding (MuDE) holography. It can achieves high and adjustable temporal resolution measurement of three-dimensional plasma distribution without delay scanning. Experimentally, we verified the feasibility of this technique, and the retrieved results of laser-plasma evolution agreed well with the direct shadow measurement. This technique is expected to provide a helpful tool for the complex spatiotemporal evolution of plasma in ICF and high energy density physics.
Vortex retarder is a simple and efficient method to generate vortex beams, and the detection of its modulation characteristics is of great significance for the preparation and application of vortex retarder. A quantitative measurement method for the two-dimensional modulation characteristics of vortex retarder based on PIE is presented. By using circularly polarized incident light, the modulation parameters of the vortex retarder are loaded into the beam phase. We report on the experimental demonstration that the high-precision reconstruction results can be achieved by applying the PIE complex amplitude measurements respectively before and after placing the vortex retarder. Based on the measurement result, the actual modulation effect of the measured vortex retarder to incident vector beam is obtained by the matrix operation and diffraction propagation. This method provides a simple and anti-interference means for quantitative detection of wave plates, liquid crystals and vortex beams.
Due to the influence of elevator pit environment, polyurethane buffer for elevator is prone to aging, resulting in its buffer performance failure. In this paper, the accelerated aging test of polyurethane buffer for elevator was carried out at different time. The mechanical properties and mass changes of the samples after different aging time were analyzed. The results show that the aging time has an obvious effect on the properties of polyurethane materials.
KEYWORDS: Crystals, Nonlinear crystals, Laser crystals, Signal to noise ratio, Modulation, Optical filters, Gadolinium, Garnet, High power lasers, Gallium
To obtain seed pulses of large energy, high contrast and broad spectral bandwidth for the high power laser system, a new cross-polarized wave (XPW) generator based on the gadolinium gallium garnet (GGG) crystal is designed. For the injected fundamental wave (FW) pulses exceeding tens of millijoule, the output XPW characteristics of conversion efficiency, spectral broadening and contrast improvement are theoretically analyzed. We also investigated the influence of spatial distribution characteristics of the injected chirped FW pulses on the output XPW. With incident FW pulses of 8 order super gaussian spatial profile for instance, conversion efficiency of ~73%, spectral broadening ratio (SBR) of ~2.7 (from 40nm to 108nm) and contrast boost by >7 orders of magnitude can be obtained. The impact of the FW spatial modulation on XPW was sensitive to the modulation depth, which is significant for spatial quality control of the laser beam in high power laser systems.
Plasma mirror is an effective approach to improve the temporal contrast of high power ultra-short laser system, while it might deteriorate the focal spot, which is reported in some experiments using plasma mirror. In order to investigate such far-field degradation by plasma mirror, we established a spatiotemporal multi-step focusing propagation algorithm based on the formula of plasma expansion and wave-front modulation model. The influence of plasma expansion time, amplitude and spatial frequency of wave-front error on focal spot degradation are quantitatively analyzed. The simulation results reveal that the far-field focal spot degradation by plasma mirror is caused by the non-uniform plasma expansion due to the wave-front error and the wave-front error with higher amplitude and lower spatial frequency has relatively greater effect on the focusing ability. From the perspective of high-contrast ultra-intense output capability, the requirement on the spatiotemporal quality of the pulse is put forward to avoid the far-field focal spot degradation when using plasma mirror in high power ultra-short laser system.
The SG II 5PW laser is designed as an open ultra-short high power laser facility that operates at the wavelength of 808nm. Three optical parametric chirped pulse amplification (OPCPA) stages are used to ensure the uncompressed pulse energy up to 260J. With a four pass zigzag compressor, the pulse width is compressed into less than 30fs and the pulse energy about 150J. By using BBO and LBO crystal, the first two OPCPA amplifiers have been accomplished this year. 35J@21fs outputs have been achieved. Since the largest size of the LBO crystal now is only about 100mm×100mm that is not enough for the needs of the third OPCPA amplifier. In our work, potassium deuterium phosphate (DKDP) as a candidate crystal has been studied theoretically and experimentally. Phase-matching parameters for various deuterium doped rate DKDP crystals are calculated. OPCPA amplifier based on 95% deuterium doped rate is designed and the output characteristics are simulated by OPA coupled wave equations. The results show that DKDP crystals with deuterium doped rate higher than 90% can be utilized in ultra-short high power laser systems that support the pulse width shorter than 30 femtoseconds. Still by estimation, when Quasi-phase-matching techniques and collinear design are used in small signal OPCPA amplification, the greatest efficiency can reach above 55%. By experiment it has proved that the output spectrum width can be more than 80nm.
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