Keyu Li

Comparison of efficient third-harmonic generation between phase modulated broadband and narrowband lasers

Based on the existing design in our prototype laser facility, the third-harmonic generation of the phase modulated broadband of 0.3 nm and narrowband lasers are theoretically analyzed and experimentally studied in this paper. The output third-harmonic generation (THG) laser characteristics such as the conversion efficiency, the spectrum distribution and the intensity modulation are compared in detail. It is found that the THG conversion efficiencies for the narrowband and such broadband lasers are fundamentally identical without spectrum narrowing. In addition, the interrelationship between THG conversion efficiency and incident fundamental light intensity for both lasers is experimentally demonstrated and the experimental results agree with the theoretical analysis. The broadband THG spectrum with ideal repetition and without loss of spectrum is obtained in the experiment.

Demonstration of broadband frequency tripling based on cascaded partially deuterated KDP crystals

The cascaded KDP crystal scheme with different deuteration levels for enhancing the bandwidth of third-harmonic generation (THG) is experimentally demonstrated in this paper. The deuteration level of a partially deuterated KDP crystal is used as a degree of freedom to alter the phase-matching (PM) wavelength. The experimental results show that this scheme can increase the bandwidth acceptance in broadband frequency tripling. In addition, the spacing between the two cascaded crystals has significant influence on the THG spectrum as well as THG conversion efficiency, and a relatively ideal THG spectrum can be obtained by the optimized parameters. Meanwhile, nonlinear-coupled wave equations are used to theoretically analyze the experimental results, and the experimental results are consistent with the numerical simulation.

Efficient Frequency Tripling of Phase Modulated Laser Based on Two KDP Mixers in Tandem Array

By using the cascaded KDP crystals, the third harmonic generation (THG) of temporal phase modulated broadband laser is experimentally demonstrated in this paper. The spectral characteristic of the generated third harmonic waves is investigated in detail. The experimental results show that the cascaded crystals method is able to satisfy the acceptance bandwidth of broadband laser beam. In addition, the influence on the THG spectrum and THG conversion efficiency of the air spacing between the two cascaded crystals is experimentally studied and it is remarkable on THG spectrum but insignificant for THG conversion efficiency. The relatively ideal THG spectrum is obtained by the optimal parameter of air spacing and the stability of THG spectrum is very good in our experiment.

Frequency conversion system design and development for the large laser facility

The design of the Large Laser Facility incorporates a type-I-type-II third harmonic generator to convert the 1.053μm fundamental wavelength of the laser amplifier to a wavelength of 0.351μm for target irradiation. To understand the design of frequency conversion system, we have carried out a series of theory researches and experiments, including parameters optimization of the third harmonic converter, experiments on high-intensity third harmonic generation (THG), researches on Transverse Stimulated Raman Scattering (TSRS) in the converting crystal and on broad-band third harmonic generation.

Investigation on high efficiency temporal phase modulated broadband second harmonic laser

In this paper, it is the first time to experimentally demonstrate the second harmonic generation (SHG) of temporal phase modulated broadband laser. The SHG conversion efficiency and the characteristic of SHG spectrum are investigated in detail and the relation between SHG conversion efficiency and incident fundamental light intensity is obtained. The highest efficiency of nearly 70% is achieved at the fundamental pulse intensity of 1.6 GW/cm2. The experimental results show that the SHG spectrum widths under high and low intensity are both half of the incident fundamental lights, and don’t result in the spectrum narrowing. The obtained results are very useful for operation at the second harmonic wavelength in inertial confinement fusion (ICF) laser facility.

Third harmonic generation of Nd:glass laser with novel composite deuterated KDP crystals

A novel composite partially deuterated KDP crystal used for frequency tripling is experimentally demonstrated for the first time in this paper. The deuteration level is used as a degree of freedom to alter the phase matching wavelength so as to increase the bandwidth acceptance. The results show that the acceptance bandwidth based on such crystal can be increased by a factor of 3 comparing with the conventional method. The obtained results are very useful to develop frequency tripling components in broadband third harmonic generation.

Broadband frequency tripling based on segmented partially deuterated KDP crystals

We report a novel frequency tripler for efficient conversion of broadband high power laser pulses at 1 μ;m. The tripler is composed of several segmented partially deuterated KDP with discrete values of deuteration. Deuteration level can be used as a degree of freedom to alter the phase-matching wavelength of a partially deuterated KDP crystal. The segmented partially deuterated KDP crystal is made by thermal bonding method. It has been shown that this new tripler is capable of enhancing the acceptance bandwidth of frequency tripling. A two-segment design is presented, which is applicable to the efficient frequency tripling of chirped pulses with a bandwidth of ~1.2-nm.

Chromatic Aberration-Eliminated Optical System of 3Ω Target Alignment Laser for SG-III Prototype Facility

To realize multi-beam positions and crystals alignment, the 3Ω target alignment laser of SG-III Prototype Facility has been designed as a reflection optical system, which avoids the effect of chromatic aberration.