High-power optical enhancement cavity is widely used in precision optical experiments and metrology. The absorption of cavity mirrors leads to the distortions of the mirror surface. Thermal deformation in a high-power optical enhancement cavity leads to a decrease in cavity gain due to alterations in the Gouy phase. In this paper, we establish the analytical relationship between mirror deformation and cavity gain by using the Winkler deformation model. The deformation exhibits an inverse proportionality to the square of the finesse. This significant result confirms the great sensitivity of gain to deformation in a cavity with high finesse.
We measured the nonlinear absorption coefficient of YVO4 using nonlinear transmittance method. The result is: for wavelength of 800nm, YVO4’s nonlinear absorption coefficient is 3.2×10-3 cm/GW for p polarization and 3.1×10-3 cm/GW for s polarization; for wavelength of 400nm, YVO4’s nonlinear absorption coefficient is 0.17cm/GW for p polarization and 0.16cm/GW for s polarization.
Based on the collision of intense laser and relativistic electrons, a Thomson scattering x-ray source can produce quasi-monochromatic x-ray pulses with high brightness in the tens keV or even higher energy regime, which can eliminate the beam hardening effect encountered in computed tomography (CT) by using polychromatic x-rays generated through Bremsstrahlung and make it possible to relate the reconstructed linear attenuation coefficients to the composition of a material. In this paper, we demonstrate the capacity of quantitative CT measurement based on Tsinghua Thomson scattering X-ray source (TTX) and the potential of anatomical segmentation using quantitative linear attenuation coefficient analysis. A peanut sample (Arachis hypogaea L.) was chosen for this study. According to the reconstructed CT image, all anatomical structures except for the testa (i.e. the seed coat) of peanut were identified clearly in terms of the shape and size, and there were high similarities between reconstructed linear attenuation coefficients of cotyledon and its theoretical values. After quantitative analysis of the reconstructed linear attenuation coefficients, the hull can be peeled off the core at the threshold of 0.31 cm-1. Our results pave the way towards fundamental researches and practical applications based on quantitative CT at TTX.
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