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Femtosecond pump-probe spectroscopy investigation of carrier dynamics in GaAlAs photocathods
摘要： Based on the study of GaAs photocathode, the carrier dynamics of re?ection-mode GaAlAs photocathode has been investigated. In this paper, the re?ection-mode GaAlAs/GaAs photocathode is grown by metal organic chemical vapor deposition (MOCVD) epitaxial technology. The femtosecond pump-probe spectroscopy is performed to measure carrier dynamics in GaAlAs and GaAs photocathods. After laser excitation the surfaces of GaAlAs/GaAs photocathode, the re?ectivity of photocathode surface is changed. At the same time, the dynamic processes of the non-equilibrium carrier distribution in semiconductor material is obtained by the transient re?ectance spectrum. Compared with GaAs photocathode, the Al element in GaAlAs photocathode is unfavorable to photoemission under some conditions, while it solves the problem that the spectrum response range of binary compounds is not adjustable. The change trend of initial relaxation transient of GaAs photocathode in the 22 ps range is the same as GaAlAs, while the change of GaAs and GaAlAs relaxation state is signi?cantly di?erent with the change of delay time after 22 ps. The results show that the GaAlAs increases band gap due to a signi?cantly slower than GaAs photocathode in initial process. Meanwhile, this paper provides a reference for the preparation of the GaAlAs photocathode that only respond to blue and green light range.
关键词： Re?ectivity,Dynamic processes,Femtosecond,Re?ection-mode,Photocathodes
更新于2025-09-23 15:23:52
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HIGHLY SELECTIVE LOSSY DUAL-BAND BANDSTOP FILTER SYNTHESIS AND DESIGN BASED ON PREDISTORTION HYBRID DUAL-BAND ELLIPTIC REFECTION FUNCTION
摘要： This paper demonstrates a new class of highly selective bandstop ?lter based on cascading two identical lossy hybrid dual-band bandstop ?lters of low resonator Q factor. Each ?lter is synthesized based on multi-stage predistortion re?ection mode technique. To demonstrate the approach, 4th order hybrid dual-band elliptic ?lter network which is a product of elliptic lowpass and highpass network functions has been predistorted and synthesized with low calculated Q factor. The lossy dual-band bandstop ?lters are fabricated and realized on microstrip planar structure. Both theoretical and experimental results clearly show good agreements with two stopband rejections up to 35 dB for one stage and 50 dB for two stages with passband loss of more than 10 dB.
关键词： microstrip planar structure,highly selective bandstop ?lter,predistortion re?ection mode technique,lossy hybrid dual-band bandstop ?lters
更新于2025-09-23 15:21:01
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Femtosecond ultrafast dynamics study on the photoemission performance of reflection-mode GaAlAs photocathode
摘要： The photoemission characteristic of re?ection-mode GaAlAs photocathode has been investigated, while a convenient and nondestructive method for evaluating the photocathode performances will be introduced. In this paper, two same re?ection-mode photocathode structures with di?erent research methods are adopted. One way is using multi-information measurement system to measure the photoemission characteristic curve of GaAlAs photocathode. Another method is the femtosecond transient re?ection spectroscopy. The ultrafast dynamics property of the GaAlAs carrier is studied with the femtosecond transient re?ectivity change, and the quantitative calculating is also shown. According to the results of two experimental methods, we analyze some photoemission performance parameters, such as carrier lifetime, di?usion length etc. The results show that the surface electron escape probability P and the drift length LDE are di?erent, while are the same of the back recombination velocity Sv by the two method. In a word, compared with multi-information measurement system, the femtosecond ultrafast dynamics method is more suitable to research on the photoemission characteristic of re?ection-mode GaAlAs photocathode which is no damage and accurate.
关键词： Femtosecond ultrafast dynamics,GaAlAs,Spectroscopy,Photocathode,Photoemission characteristic,Re?ection-mode
更新于2025-09-19 17:15:36