Measurement of ultrashort optical pulses by two-photon photoconductivity techniques

Abstract

Two-photon conductivity in GaAs and CdS0.,Seo., were investigated with modelocked Nd:glass laser pulse excitation, with a view to determine their suitability for picosecond pulsewidth measurement. The contrast ratio using GaAs as twophoton conductor was 1.8 and it increased to 2.4 when CdSo.,Seo., was used. The improved contrast ratio in the case of CdSo.,Seo., was partly due to the improved resolution of the crystal (2 ps) and partly due to the extended square-law region.

Competition between sub-bandgap linear detection and degenerate two-photon absorption in gallium arsenide photodiodes

“…During the lifetime of this state, given by the second Heisenberg principle τ ≥ 2(E g −E) , a second photon with enough energy can complete the transition, hence creating an electron-hole pair and generating a photocurrent, named two-photon current (TPC). As the lifetime of this intermediate state is very short in visible gap material (in the fs range), this process is particularly well suited for ultra fast correlation measurements [3][4][5][6]. However, the very short lifetime of the virtual state is also responsible for the intrinsically low *Correspondence: baptiste.fix@onera.fr 2 ONERA, Chemin de la Hunière, 91761 Palaiseau Cedex, France Full list of author information is available at the end of the article efficiency of this process, as it requires the quasi simultaneous occurrence of two photons in this time interval.…”

Single-frame measurement of complex laser pulses tens of picoseconds long using pulse-front tilt in cross-correlation frequency-resolved optical gating

“…The main approach for measuring many-ps-long pulses has long been multishot intensity autocorrelation using a delay-scanning stage and such optical nonlinearities as second-harmonic generation (SHG) [45][46][47], two-photon photoconductivity [48,49], two-photon fluorescence [50,51], and high-order effects [52,53]. Multishot interferometric autocorrelation [54,55], also using a scanning delay stage, has also been used.…”

Properties of phase-shifting devices used in researches of nonlinear absorption

“…Operation of optical processors [1], switches [2], logical elements [3], autocorrelators [4,5] and other bistabile elements [5,6] based on the using of two-photon absorption. Uniaxial crystals can be utilized as material for these devices [6]. If azimuth of polarization   m / 2 ( is the angle between the crystal optical axis С and the vector Е of electromagnetic wave, m = 0, 1, 2, 3,...), in a crystal two light beams spread in the same direction (ordinary with ЕС and extraordinary with Е‫||‬С waves).…”