Sensitive and accurate femtosecond pulse characterization via two-photon absorption in Fabry-P\'erot laser diodes

TL;DR

This paper demonstrates that Fabry-Pérot semiconductor laser diodes can be used as sensitive, accurate two-photon detectors for femtosecond pulse characterization, offering a compact alternative to traditional autocorrelation methods.

Contribution

It provides a systematic analysis of laser diodes' ability to measure femtosecond pulse widths, validating their use for interferometric autocorrelation at room temperature.

Findings

Accurately measured femtosecond pulses down to 36 fs.

Validated diode-based autocorrelation against standard methods.

Showed diode structures can detect low-energy pulses with high precision.

Abstract

Semiconductor lasers offer native bifunctionality enabling coherent light emission and linear photodetection. They can also operate as sensitive two-photon absorption detectors due to the third-order nonlinearity of the heterostructure constituting the active region. The strong two-photon response at room temperature is highly desired in ultrafast optics, where such detectors are used for interferometric characterization of femtosecond light pulses for shape and duration. Another niche is pulse detection in dual-comb ranging. While prior studies have focused on the two-photon response of commercial photodiodes or proprietary semiconductor microcavities for intensity autocorrelation measurements, a systematic analysis of the semiconductor lasers ability to accurately characterize the optical pulse width is missing. To address this niche, here we measure autocorrelation traces of femtosecond pulses with varying durations from sub 55 fs to 260 fs at the common 1.5 $\mu$m wavelength using AlGaAs and InGaAsP laser diodes designed to operate at emission wavelengths of 0.95 $\mu$m and 1.3 $\mu$m, respectively. We validate the obtained waveforms using a silicon avalanche photodetector and conventional crystal-based second-harmonic autocorrelator. We consider the effects of optical polarization, operation mode and electrical load resistance on the shape and intensity of generated electrical signals. Our results prove the suitability of Fabry-P\'erot laser structures for interferometric autocorrelation measurements of 53 $\mu$W (220 fJ pulse energy) average power pulses as short as 36 fs with a mean square error of 7 $\times$ 10$^{-3}$.