Experimental demonstration on 400†nm-scale bandwidth optical parametric chirped-pulse amplification based on mixed cascaded crystals.

We present an optical parametric chirped-pulse amplification (OPCPA) based on mixed cascaded crystals, taking advantage of the unique parametric phase-matching of lithium triborate (LiB3O5, LBO) and yttrium calcium oxyborate ((YCa4O(BO3)3, YCOB) crystals. The OPCPA properties of LBO at 880 nm and YCOB at 750 nm are studied respectively. After amplification by two LBO and two YCOB crystals, a total signal gain of 108 and spectral bandwidth close to 400 nm is obtained. After accurate dispersion compensation with a grating-pair compressor and chirped mirror compensator, a pulse duration of 9.4 fs is obtained by a SHG-frequency-resolved optical grating (FROG). This approach will be of great significance in high energy amplifier for high peak power few-cycle laser sources.

Efficient generation of mid-infrared few-cycle pulses by the intrapulse difference-frequency generation in YCOB.

Yttrium calcium oxyborate (YCOB) crystals have been widely applied for generating intense near-infrared laser pulses by optical parametric amplification. Here, we show that the YCOB crystals oriented in both the XZ and XY principal planes possess broadband phase-matching property of intrapulse difference-frequency generation in the mid-infrared region. Few-cycle pulses tunable from 2 to 4 µm are experimentally produced by using a 7.5-fs pump laser at 800 nm, in which the conversion efficiency can be as high as 2.5%. With a large-size crystal and high-power pump laser, intrapulse difference-frequency generation based on YCOB may provide a new route for directly producing intense few-cycle mid-infrared pulses.

Demonstration of 85% pump depletion and 10-6 noise content in quasi-parametric chirped-pulse amplification.

Full pump depletion corresponds to the upper limit of the generated signal photons relative to the pump pulse; this allows the highest peak power to be produced in a unit area of ultraintense laser amplifiers. In practical systems based on optical parametric chirped-pulse amplification, however, the typical pump depletion is only ~35%. Here, we report quasi-parametric chirped-pulse amplification (QPCPA) with a specially designed 8-cm-thick Sm:YCOB crystal that highly dissipates the idler and hence improves pump depletion. We demonstrate 56% QPCPA energy efficiency for an 810-nm signal converted from a 532-nm pump, or equivalently 85% pump depletion. As another advantage, such a record high depletion greatly suppresses the parametric superfluorescence noise in QPCPA to only ~1.5 × 10-6 relative to the amplified signal energy. These results pave the way to beyond the ten-petawatt peak power of the currently most intense lasers.

Ultra-broadband high conversion efficiency optical parametric chirped-pulse amplification based on YCOB crystals.

We present a high efficiency and ultra-broadband optical parametric chirped-pulse amplification (OPCPA) system fully based on yttrium calcium oxyborate (YCOB) crystals. The OPCPA properties of YCOB at 808 nm are studied for both high gain and saturated amplification. The non-collinear angle is finely tuned to study the variation of gain spectrum at a certain phase-matching angle of YCOB crystals. After amplification by four YCOB crystals, a total signal gain of 0.9×109 is obtained and the FWHM spectral bandwidth is still over 100 nm. An amplified signal pulse of 182 mJ is achieved with pump energy of 440 mJ in the saturated amplification stage and the conversion efficiency is about 40%. After a four-grating compressor, a pulse duration of 20 fs is measured by a second-order autocorrelator.