In order to research the influence on the beam quality due to thermal deformation of the secondary mirror in the high power laser system, the theoretical simulation study is performed. Firstly, three typical laser power 10kW, 50kW and 100kW with the wavelength 1.064μm are selected to analyze thermal deformation of mirror through the finite element analyze of thermodynamics instantaneous method. Then the wavefront aberration can be calculated by ray-tracing theory. Finally, focus spot radius，beam quality (BQ) of far-filed beam can be calculated and comparably analyzed by Fresnel diffraction integration. The simulation results show that with the increasing laser power, the optical aberration of beam director gets worse, the far-field optical beam quality decrease, which makes the laser focus spot broadening and the peak optical intensity of center decreasing dramatically. Comparing the clamping ring and the three-point clamping, the former is better than the latter because the former only induces the rotation symmetric deformation and the latter introduces additional astigmatism. The far-field optical beam quality can be improved partly by simply adjusting the distance between the main mirror and the secondary mirror. But the far-field power density is still the one tenth as that without the heat distortion of secondary mirror. These results can also provide the reference to the thermal aberration analyze for high power laser system and can be applied to the field of laser communication system and laser weapon etc.
High average power pulsed TEA CO<sub>2</sub> lasers have many important applications, such as laser manufacturing, military applications, but there rarely have reports about the theoretical and experimental studies on the virtual confocus resonator of pulsed TEA CO<sub>2</sub> laser, especially its far field optical quality. Based on the real date of the unstable resonator modified by the stable resonator of high power TEA CO<sub>2</sub>, three common theoretical evaluations and analyzes were conducted and compared with the measured results of far field light intensity distribution with 2 kW designed unstable resonator laser with the block ratio is ε=0.404. The results show that the unstable resonator can obtain near diffraction limitation and high optical quality beam. The β factor is smaller than 4 times than the stable resonator. Furthermore, the smaller block factor can make higher power in bucket for the unstable resonator. The comprehensive prediction and evaluation of designed unstable resonator need to synthetically use these three theoretical methods of the evaluations. The simulation results, with considering the optical aberration, heat distortion and atmospheric effect, agree well with the real recording image by the infrared imaging system in the distance of 300m. The research of this paper has very important reference value for evaluating the tactical effectiveness and optimization design of high power TEA CO<sub>2</sub> laser system with different unstable resonators.
It is always the hot subject to realize the output of high-power laser in the range of 3-5μm wavelength. This rang of wave
band has greatly important applications in military because it located in the atmosphere window. Generally there are two
ways to obtain this range of laser wavelength. One way is through optical parameter oscillation (OPO) from shorter laser
wavelength and the other is through second harmonic generation (SHG) from longer laser wavelength. Firstly, the
comparison between tow nonlinear crystals ZnGeP<sub>2</sub> and AgGaSe<sub>2</sub> is conducted for their nonlinear coefficient and
damaging threshold in theory. The theoretical results show that the crystal AgGaSe<sub>2</sub> is more suitable for the SHG of pulsed
TEA CO<sub>2</sub> laser. When using pulsed TEA CO<sub>2</sub> laser with wavelength of 9.3μm to pumping AgGaSe<sub>2</sub> SHG crystal, the
wavelength of 4.65μm is obtained. In the condition of repetition rate 100Hz, the upmost output power of single pulse is up
to level of 1W, which corresponding efficiency of SHG is about 6%. The experimental results show that the polarization of
laser beam has greatly influence on the SHG output of the crystal. Under the radiation of 3MW/cm<sup>2</sup> from fundamental
wave and the right position for maximal SHG output in the crystal, when polarization of laser beam rotates ±4.5°, the SHG
output of energy decrease about 30%. The research of this paper will make a foundation for further development of
A recent experiment on Stark effect spectroscopy in self-assembled quantum dots (SADs) has demonstrated the existence of an inverted electron-hole alignment due to the presence of gallium diffusion in InAs SADs and has established a relation between the Stark shift and the vertical electron-hole separation. The theoretical interpretation of these experimental results is based on the assumption that the applied electric field can be treated by the second-order perturbation theory, which results in a quadratical dependence of the transition energy on the applied electric field. While this relation is well satisfied in many quantum systems including single SADs and quantum well structures. But this relation is not valid for vertically coupled SAD structures, the asymmetric Stark shift of experimental measurement has shown existence of built-in dipole moment in InAs/GaAs QDs. Here we present a theoretical investigation of the factors influencing the sign and magnitude of the built-in dipole moment in realistic QD structures, including cubical, pyramidal and truncated pyramidal shape. The comparable results gave a reasonable interpretation for the experimental results.
Our calculations consist of two basic steps. First, the strain is calculated for particular dot geometry with Green function methods. Second, the single-electron states are calculated using an electronic Hamiltonian, which depends on the strain. The computed states can then be used to determine various quantities, such as optical transition strengths, or exciton binding energies. In the article, we use Green function for the strain calculation, and plane-waves expansion in the envelope function approximation for the electronic structure calculations. The theoretical results agree well with the available experimental data. Our calculated results are useful for the application of QDs to photoelectric devices.
In this paper, performance of holographic storage based on doubly doped Fe:Mn:LiNbO<sub>3</sub> crystal with 0.03 wt% Fe<sub>2</sub>O<sub>3</sub> and 0.1 wt% MnO dopants which was great contrastive against previous investigations was studied theoretically and experimentally. We established the coupling differential equations using the band-transport model. Using practical experiment parameters, we numerically calculated and explained the time-dynamic developing process of the holographic storage, and analyzed how the oxidation-reduction degree of the crystal affects the space charge field within the crystal. Only the oxidative crystals can accomplish nonvolatile holographic storage but not the reductive crystal. For the oxidative crystal, its remaining magnitude of the space charge field increases with the increase of oxidative degree. Further more we measured the diffraction efficiencies of four specimens with different degree of oxidation-reduction and realized holographic multiplying and holographic fixing in the oxidation crystal successfully. Based on the experiments, we also calculated both the dynamic range parameter M/# of the oxidized doubly doped Fe:Mn:LiNbO<sub>3</sub> crystal and the recording sensitivity of various crystals. The experimental results coincided with the theoretical analysis very well. Diffraction efficiency of fixing grating increased with oxidation, photorefractive sensitivity decreases with oxidation, higher the concentration of doped manganese and oxidation, the larger the effective dynamic range of holographic storage system is, where holograms can be stored permanently.