Two-photon absorption autocorrelation of visible to ultraviolet femtosecond laser pulses using ZnS-based photodetectors

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Abstract
In this letter, we demonstrated an autocorrelator based on two-photon absorption (TPA) of ZnSSe photodetectors, which is capable of measuring femtosecond laser pulses from 800 to 400 nm. This broad bandwidth autocorrelator has high sensitivity and is capable of measuring laser pulses as short as 27 fs and pulse energy of a few picojoules. These results could lead to cost-effective ultrafast autocorrelator with a single detector head to cover the whole visible to near ultraviolet spectral region. Our TPA measurement shows that the defect and impurity states below the bandgap (E/sub g/) have detrimental effect for excitation wavelengths near the bandedge, however, these states are also beneficial by extending the operation wavelengths of the detector beyond E/sub g//2. Using a ZnMgS photodetector with a larger E/sub g/ enables the autocorrelator to be more sensitive at 400 nm, and extends the responsivity further into the ultraviolet wavelengths.