Broadband amplification by picosecond OPCPA in DKDP pumped at 515 nm

Characteristics of broadband OPCPA based on DKDP crystals with different deuterations for the SEL-100 PW laser system

We present the performances of a broadband optical parametric chirped pulse amplification (OPCPA) using partially deuterated potassium dihydrogen phosphate (DKDP) crystals with deuteration levels of 70% and 98%. When pumped by a Nd:glass double frequency laser, the OPCPA system using the 98% deuterated DKDP crystal achieves a broad bandwidth of 189 nm (full width at 1/e2 maximum) from 836 nm to 1025 nm. For the DKDP crystal with length of 43 mm, the pump-to-signal conversion efficiency reaches 28.4% and the compressed pulse duration is 13.7 fs. For a 70% deuterated DKDP crystal with a length of 30 mm, the amplified spectrum ranges from 846-1021 nm, the compressed pulse duration is 15.7 fs, and the conversion efficiency is 25.5%. These results demonstrate the potential of DKDP crystals with higher deuteration as promising nonlinear crystals for use as final amplifiers in 100 Petawatt (PW) laser systems, supporting compression pulse duration shorter than 15 fs.

Rapid growth technology and optical properties of a large aperture high-deuterium DKDP crystal

In this paper, a concept of establishing a uniform temperature field range and a “double-layer four-stage continuous filtration circulation system (DF-CFCS)” during crystal growth have been proposed.

Numerical analysis of the DKDP-based high-energy optical parametric chirped pulse amplifier for a 100 PW class laser

An optical parametric chirped pulse amplifier (OPCPA) based on a large-aperture DKDP crystal and pumped by a 10 kJ level Nd:glass laser can serve as the final amplifier for a 100 PW level laser. A comprehensive numerical investigation on such a high-energy OPCPA is presented in this work. The effects on the efficiency-bandwidth product induced by the deuteration level, absorption loss, temperature variation, and optimization of zero-phase-mismatch wavelength (ZPMW) are analyzed in detail. Based on the analysis above, a three-dimensional numerical simulation taking into account the effects of pumping depletion, diffraction, and walk-off shows that, by optimization of ZPMW, broadband (over 210 nm spectral width in FWHM) and high efficiency (${\gt}37\%$) amplification can be realized in the DKDP crystal even with a moderate deuteration level of 70%, which can relax the requirement of a high deuteration level in a large-aperture DKDP crystal. The numerical analysis can provide meaningful guidance for the design and construction of 100 PW class laser systems.

Phase Compensation Method in OPA System Based on the Linear Electro-Optic Effect

Factors such as mechanical deformation and temperature changes lead to phase mismatch in optical parametric amplification systems, impacting energy stability. A phase compensation method via the linear electro-optic effect can overcome this limitation. Phase mismatch compensation characteristics were simulated via the linear electro-optic effect in 70%-deuterated DKDP and 95%-deuterated DKDP. This method was applied to OPA systems to verify its feasibility. The results show that the temperature acceptance bandwidth of 70%-deuterated DKDP and 95%-deuterated DKDP can be ~1.75 and ~2 times larger, respectively, than that of the OPA without compensation. Moreover, the angle acceptance bandwidth of 70%-deuterated DKDP and 95%-deuterated DKDP can be ~2 times larger than that of the OPA without compensation. The abovementioned method can facilitate the compensation of phase mismatch within a range and can be widely used in OPA and optical parametric chirped pulse amplification systems to improve laser stability.

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.

Broadband main OPCPA amplifier at 808 nm wavelength in high deuterated DKDP crystals

The optical aperture of ultrashort extreme intensity laser facilities, which reach 10 PW, will be beyond several hundred millimeters. DKDP is by now the only nonlinear crystal that can be grown to such diameter and used in the main optical parametric chirped-pulse amplification (OPCPA) amplifier of such a laser system. Here, at the signal wavelength of 808 nm for the first time, we experimentally present a broadband OPCPA system that consists of a pre-amplifier in BBO crystals and a main OPCPA amplifier in two 95% deuterated DKDP crystals. The final amplified spectrum bandwidth exceeds 50 nm, and a compressed pulse duration of 27 fs has been measured. The conversion efficiency of the main OPCPA amplifier reached 24%, and a net signal gain of 13 was obtained. For the high energy OPCPA amplifier, the influence due to partial absorption on the idler pulses in DKDP crystal is theoretically analyzed. The results indicate the potential utilization of high deuterated DKDP for the main OPCPA amplifiers in a multi-petawatt laser system at 808 nm wavelength.

Highly efficient, cascaded extraction optical parametric amplifier

The scheme of cascaded extraction optical parametric amplifier (CE-OPA) has been proposed as a final amplifier for high peak power laser systems. 4D numerical simulations show that conversion efficiency of a CE-OPA system pumped with a temporal Gaussian pump pulse is as close to the theoretical limit of quantum efficiency as a conventional OPA pumped with temporal flat-top pump pulse. The CE-OPA system is also similar to the conventional scheme in output energy stability and alignment sensitivity of the phase-matching angles, too. However, with the use of the CE-OPA scheme, the requirement of pump pulse shaping can be relaxed, leading to an overall higher plug in efficiency as well as compact design.

Generation of multi-octave spanning high-energy pulses by cascaded nonlinear processes in BBO

We present the generation of optical pulses with a spectral range of 500-2400 nm and energies up to 10 µJ at 1 kHz repetition rate by cascaded second-order nonlinear interaction of few-cycle pulses in beta-barium borate (BBO). Numerical simulations with a 1D+time split-step model are performed to explain the experimental findings. The large bandwidth and smooth spectral amplitude of the resulting pulses make them an ideal seed for ultra-broadband optical parametric chirped pulse amplification and an attractive source for spectroscopic applications.

Linear and nonlinear optical properties of terbium calcium oxyborate single crystals

The linear and nonlinear optical properties of TbCa4O(BO3)3 (abbreviated as TbCOB) single crystals were investigated for the first time. The refractive indices of TbCOB at several wavelengths were measured by using the minimum deviation method and the parameters of Sellmeier's dispersion equation were determined from the experimental data. The complete set of six second-order nonlinear optical (NLO) coefficients of TbCOB single crystals were obtained using the Maker fringe (FM) technique, with the largest d32 being on the order of 1.65 pm/V. Moreover, the phase-matching (PM) configurations of second-order harmonic generation (SHG) in the principal planes were calculated, and the largest effective NLO coefficient is deff = 0.86 pm/V along (22.56°, 180°) PM direction. The SHG conversion efficiency from 1064 nm to 532 nm of 8 mm long crystal samples without AR coating along this direction was achieved 57.1% at 28.2 mW input power, and it has a small walk-off angle of 13.8 mrad. In addition, the comparison and discussion with GdCOB and YCOB were carried out.

Reverse engineering of multilayer coatings for ultrafast laser applications

We propose a reliable reverse engineering approach for a postproduction characterization of complicated optical coatings for ultrafast laser applications. We perform the postproduction characterization on the basis of in situ broadband monitoring data and validate the results using ex situ transmittance data and group delay measurements.

Pump-seed synchronization for MHz repetition rate, high-power optical parametric chirped pulse amplification

We report on an active synchronization between two independent mode-locked lasers using a combined electronic-optical feedback. With this scheme, seed pulses at MHz repetition rate were amplified in a non-collinear optical parametric chirped pulse amplifier (OPCPA). The amplifier was seeded with stretched 1.5 nJ pulses from a femtosecond Ti:Sapphire oscillator, while pumped with the 1 ps, 2.9 µJ frequency-doubled output of an Yb:YAG thin-disk oscillator. The residual timing jitter between the two oscillators was suppressed to 120 fs (RMS), allowing for an efficient and broadband amplification at 11.5 MHz to a pulse energy of 700 nJ and an average power of 8 W. First compression experiment with 240 nJ amplified pulse energy resulted in a pulse duration of ~10 fs.