High-fidelity device for single-shot pulse contrast measurement based on quasi-phase-matching (QPM)

A high-fidelity device for single-shot pulse contrast measurement based on quasi-phase-matching (QPM), comprising a generating unit of sampling pulse, a high-fidelity cross-correlation unit of nonlinear sum frequency generation (SFG) and a high-sensitivity signal detecting unit, wherein a beam splitter is for dividing a near-infrared laser pulse emitted by a laser source into a first part of a sampling pulse and a second part of an under-test pulse;

• said generating unit comprises an optical parametric amplification-optical parametric generation (OPA-OPG) system, a first retarder, a first filter and two telescopes, wherein a part of a pulse laser emitted by a near-infrared light source is orderly contracted by said telescope and delayed in time by said retarder to pump said OPA-OPG system to produce a sampling pulse having a mid-infrared waveband and cleaner than the under-test pulse;
• said high-fidelity cross-correlation unit comprises a nonlinear correlation crystal, a second retarder, a periscope, two telescopes and two plano-concave cylindrical lenses, wherein a polarization direction of the under-test pulse is changed by said periscope to be the same as that of the sampling pulse, wherein the sampling pulse and the under-test pulse are respectively expanded by said respective telescope and one-dimensionally focuses onto said nonlinear correlation crystal by said two respective plano-concave cylindrical lenses, in which the sampling pulse and the under-test pulse are correlated at a non-colinear angle of 30 degrees to 40 degrees and in a phase matching method of e+e→e to produce a correspondent SFG correlation signal distributed along the transverse space, and wherein said nonlinear correlation crystal is made through periodically polarizing only a part of a relatively long lithium niobate (LNB) crystal, which means the LNB crystal is elongated compared to a common LNB crystal and has only said part periodically polarized;
• said high-sensitivity signal detecting unit comprises a dot-mirror or dot-attenuator, a neutral attenuating plate, three plano-convex cylindrical lenses, a fiber array, a second filter and a highly sensitive and quickly answering photomultiplier tube (PMT), wherein said fiber array comprises 64 to 126 fibers gradually elongated at regular space and fiber attenuators of different attenuation multiples are respectively attached with said fibers based on different signals of each channel;
• the correlation signals distributed along the space is change by said fiber array into a series of pulses with equal time intervals and relatively uniform intensities;
• the series of pulses pass through said second filter and are received and changed into electric signals by said PMT;
• a computer analyzes the electric signals to produce a contrast curve of the under-test pulse;
• said OPG-OPA system is an optical parametric generation-optical parametric amplification system.