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Sensitive Infrared Photon Counting Detection by Nondegenerate Two-Photon Absorption in Si APD
摘要： We report on the sensitive detection of photons at broadband infrared wavelengths based on the nondegenerate two-photon absorption in the Si avalanche photodiodes. The detected 1700~1850 nm infrared photon energy is lower than Si band gap and the energy difference is complemented by a high intensity pump laser field at 1550 nm. It is thus possible to capitalize on the low noise property of large band gap materials for detecting low energy photons. And the linear intensity response of the detector to the incident infrared photons was observed when the power of pump laser was about 12.42 μW, indicating the dominance of nondegenerate two-photon absorption in the infrared photon detection. An enhancement factor of 20 was observed for the incident signal photon numbers of ~0.14×106 photons per pulse. We offer an alternative to sensitive detection of infrared light. This may also provide new ideas for broadband infrared photon detection in different applications such as optical comb laser ranging, infrared bio-image and so forth.
关键词： Infrared photon detection,silicon avalanche photodiode,nondegenerate two photon absorption
更新于2025-09-16 10:30:52
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Temporally Resolving Synchronous Degenerate and Nondegenerate Two-Photon Absorption in 2D Semiconducting Monolayers
摘要： Degenerate and nondegenerate two-photon absorption (TPA) in WS2 and MoSe2 monolayers are synchronously induced and temporally resolved by femtosecond laser pump-probe. Di?erential transmission signals in the ?rst 500 fs consist of negative and positive components, that originate from direct probe depletion via nondegenerate TPA and carrier accumulation via degenerate TPA, respectively. Temporal cross-correlation of pump and probe pulses allows us to fully decouple the ultrafast nondegenerate and degenerate TPA signals. Subsequently, degenerate and nondegenerate TPA coe?cients are calculated as a function of pump irradiance. Under nonresonant pumping, 100 ± 10 and 250 ± 25 cm GW?1 are obtained for degenerate and nondegenerate TPA coe?cients of monolayer WS2, respectively, which both present linearly decreasing trends as increasing pump irradiances. However, under resonant pumping of 2 p excitonic states in monolayer MoSe2, degenerate TPA coe?cients exponentially decrease from 800 to 80 cm GW?1 as increasing pump irradiances, due to the interplay between band-renormalization and band-?lling e?ects, while nondegenerate TPA coe?cient is about 650 ± 50 cm GW?1. For comparison, a trilayer MoSe2 is also investigated. These results set a foundation for precisely measuring TPA coe?cients and actively controlling nonlinear excitonic dynamics via TPA in 2D semiconducting monolayers.
关键词： 2D monolayer,transition metal dichalcogenide,femtosecond laser pump-probe,nondegenerate two-photon absorption,degenerate two-photon absorption
更新于2025-09-04 15:30:14