Researchers from the Key Laboratory of High Power Laser and Physics, Shanghai Institute of Optics and Fine Mechanics (SIOM) of the Chinese Academy of Sciences (CAS) have made progress in the deep-UV laser generation using KH₂PO₄ (KDP)-family crystals. The results were published in Optics Letters with the title "Noncritical phase-matching fourth- and fifth-harmonic generation of 1077 nm laser using KDP-family crystals" on June 2, 2022.

Deep-UV laser has important applications in many fields, such as precision machining, plasma diagnostics, and the detection of physical and chemical processes, because of its significant advantages of short wavelength and high spatial-temporal resolution. At present, one of the most commonly used methods to obtain deep-UV laser is based on nonlinear optical technology via the fifth harmonic generation of 1-micron waveband laser.

Owing to severe laser damage of optical materials in a high-intensity regime, there is an insurmountable upper limit for applicable laser pulse energy and power per unit area, especially for the deep-UV spectral region. To generate high-flux laser radiation in this wave band, the use of large-aperture crystals is almost the only effective way. For the KDP-family crystals such as NH₄H₂PO₄ (ADP) and KDP crystals, because of the phase-matching limitation, most of the experiments were demonstrated at low temperatures. Their applications and the increase of output energy are facing great challenges.

Aiming the above problems, by theoretically calculating the phase-matching temperature required for the fourth- and fifth-harmonic generation in KDP family crystals at different wavelengths, and using optical parametric amplification to generate a 1077 nm laser, the researchers systematically demonstrated that the noncritical phase-matching fourth- and fifth-harmonic generation of 1077 nm laser can be realized in ADP, KDP and DKDP crystals under noncryogenic conditions. For ADP and DKDP crystals, noncritical phase-matching fourth-harmonic generation of 1077 nm laser were realized at 74.0 ℃ and 132.5 ℃, respectively. For the fifth-harmonic generation, noncritical phase matching was achieved in KDP crystal at 48.5 ℃.

The results pave the way for high-energy and high-power deep-ultraviolet laser generation using KDP-family crystals under noncryogenic conditions.

Fig. 1 Schematic diagram of experiment. (Image by SIOM)

Fig. 2 Fifth-harmonic generation of 1077 nm laser in KDP crystal. (Image by SIOM)

Article website:
https://doi.org/10.1364/OL.458952

Contact:
WU Xiufeng
General Administrative Office
Shanghai Institute of Optics and Fine Mechanics, CAS
Email: xfwu@siom.ac.cn
Web: http://english.siom.cas.cn/