Articles in press have been peer-reviewed and accepted, which are not yet assigned to volumes/issues, but are citable by Digital Object Identifier (DOI).
, Available online , doi: 10.3788/IRLA20200140
In order to meet the needs of low power consumption methane detection technology, an ultra-low power consumption infrared methane sensor and system based on non-dispersed infrared spectroscopy is developed, which is based on the characteristics of methane gas molecules having main absorption peak in the infrared band of 3.2 μm~3.4 μm. The selection of LED and PD devices and the design of optical path are studied based on the analysis of the principle of infrared differential detection. The power consumption of infrared methane sensor is reduced to 10 mW by using LED packets of pulses current drive technology. The influence of temperature change on the measurement of methane concentration is studied by experimental method, the temperature compensation algorithm formula is obtained by data analysis and linear fitting of normalization method. The performance experiment is carried out on the detection system platform, and the basic performance parameters are given. The system has the advantages of low power consumption, anti-interference of water vapor and good detection stability, and has important application value.
, Available online , doi: 10.3788/IRLA202049.20200038
Depolarization mechanism and compensation scheme of radially polarized beams under non-uniform pumping are investigated. Theoretical analysis shows that, for the non-uniform pumping status, the thermal induced shear birefringence caused by the thermally induced shear stress within the cross-section of the isotropic crystal is the main reason for the depolarization of the radially polarized beams. Related experiments were designed to evaluate the depolarization of the radially polarized beams which under non-uniform pumping conditions by using two methods of thin-film polarizer (TFP) measurement and purity measurement, in which the TFP measurement method is used to detect the overall depolarization of radially polarized beams and the purity measurement method is used to detect local depolarization of radially polarized beams. With a peak pump power of 1.1 kW, the depolarization measured by the two evaluation methods is 2.34% and 2.53%, respectively. Based on the theoretical analysis and evaluation results, a combination of phase modulation and spatial mode matching was considered in the design of the depolarization compensation scheme, which improved the depolarization of the radially polarized beams by 59%. Meanwhile, a picosecond radially polarized beam with a pulse energy of 19.36 mJ, a purity of 90.13%, and a beam quality M2 factor of 3.8 was achieved.
, Available online
The amplification of both continuous-wave (CW) and pulsed backward signal in high-power master-oscillator-power-amplifier based fiber laser are investigated using rate equation model. The results show that the CW backward light would be amplified significantly by the high-power amplifier and thus decrease the laser output seriously. For the pulsed backward signal, the pulse energy would not be amplified obviously since the energy storage is absent in CW fiber laser. Considering the damage threshold of the fiber and devices including end-cap and fiber Bragg grating (FBG), the amplification of CW backward light may damage the FBG of the laser oscillator, and the backward laser pulse with millijoule level pulse energy may damage the fiber, while there also exists the risk of end-cap damage when pulsed backward laser incidents.
, Available online
In view of the thermal damage law and mechanism of monocrystalline silicon for millisecond pulsed laser, the temperature of monocrystalline silicon irradiated by millisecond pulsed laser is measured by high precision point temperature meter and spectral inversion system. Then the temperature evolution process is analyzed. Also, the temperature state during the whole process of thermal damage of monocrystalline silicon irradiated by millisecond pulsed laser and the corresponding damage structure are studied. The results of this study show that the peak temperature of laser-induced monocrystalline silicon increases with the increase of energy density when the pulse width is fixed, When the pulse width is between 1.5 ms-3.0 ms, The temperature decreases with the increase of pulse width. Temperature rise curve shows inflection point when it is close to the melting point (1687 K), the reflection coefficient is from 0.33 to 0.72. During the gasification and solidification stages, it also shows the gasification and the solidification plateau periods. Thermal cleavage damage of monocrystalline silicon precedes thermal erosion damage. Stress damage dominates under low energy density laser irradiation, while thermal damage dominates under high energy density laser irradiation. The damage depth is proportional to the energy density and increases rapidly with the increase of the number of pulses.