Abstract
A wavelength swapping nondegenerate pump-probe technique to measure the magnitudes of the nonlinear optical dynamics as well as the relaxation time of electrons in high energy levels is presented using a ZnS single crystal wafer as an example. By pumping the sample with 800 nm femtosecond pulses and probing at 400 nm, nondegenerate two-photon absorption (N-2PA) happens exclusively, and the measured curves only show instantaneous features without relaxation tails. The N-2PA coefficient was derived explicitly as 7.52 cm/GW. Additionally, when the wavelengths of the pump and probe beams are swapped, extra information about the relaxation time of the hot electrons excited in the conduction band is obtained. The combined results above are helpful for evaluating the characteristics of an optical switches based on ZnS or other materials with respect to its nonlinear optical dynamic aspect.
Highlights
One of the prime goals of current optics and photonics is to realize optical switches that can process information at unprecedented speed.[1]
A wavelength swapping nondegenerate pump-probe technique to measure the magnitudes of the nonlinear optical dynamics as well as the relaxation time of electrons in high energy levels is presented using a zinc sulfide (ZnS) single crystal wafer as an example
The response speeds of the electronic transistors are mainly limited by their inner capacities and resistances while the ultimate speeds of the optical switches are closely related to the relaxation time of the free carriers generated in high energy levels.[6,7]
Summary
One of the prime goals of current optics and photonics is to realize optical switches that can process information at unprecedented speed.[1]. Time of hot electrons in high levels simultaneously, i.e. the properties of the optical switch recovery time did not capture much interest before. We take a zinc sulfide (ZnS) single crystal wafer as an example to present a wavelength swapping nondegenerate pump-probe technique to measure both the magnitudes and the temporal properties of the nonlinear optical dynamics. Through pumping the sample by 800 nm pulses and probing at 400 nm, nondegenerate two-photon absorption (N-2PA) happens exclusively, and the measured curves show only instantaneous features without relaxation tails appear. In order to get the relaxation properties of the hot electrons in the high level, the wavelengths of the pump and probe beams are swapped. Additional degenerate two-photon absorption (D-2PA) happens, and the relaxation time of the hot electrons excited in the conduction band is measured as 0.35 ns. Information is helpful to evaluate the performance of an optical switch based on ZnS crystals
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