Thermal stable nonlinear Raman-Nath diffraction and Cherenkov radiation in PPKTP crystals

Abstract

Nonlinear Raman-Nath diffraction (NRND) and nonlinear Cherenkov radiation (NCR) are significant nonlinear diffraction phenomena in optics. Previous studies have primarily focused on NRND and NCR in uniaxial crystals, particularly in periodically poled lithium niobate (PPLN) crystals. However, research on these phenomena in biaxial crystals, such as periodically poled potassium titanyl phosphate (PPKTP), has been limited, and the study of NCR in PPKTP has not yet been undertaken.In this work, we experimentally investigated NRND and NCR phenomena in PPKTP crystals under varying incident angles, pump polarizations, poling periods, and crystal temperatures. Our findings indicate that PPKTP exhibits over ten times greater thermal stability compared to PPLN. This high thermal stability is promising for applications in parallel optical computing, as it helps reduce optical mode deviations and minimize bit error rates.

Figures (10)

• Figure 1: Phase-matching conditions and experiment setup. (a) Quasi phase-matching (QPM), (b) Nonlinear Raman–Nath diffraction (NRND), (c) Nonlinear Cherenkov radiation (NCR) and (d) Nonlinear Bragg diffraction (NBD), (e) Experiment setup. Here, $k_1$ is the wave vector of the pump laser, $k_2$ is the wave vector of the second harmonic laser, $G$ is the reciprocal lattice vector, and $\theta$ is the diffraction angle of the second harmonic.
• Figure 2: NCR and $m^\mathrm{th}$‐order NRND patterns recorded in the PPKTP with a poling period of 9.83 $\mu$m at different polarizations and incident angles. (a)-(c) represent the second-harmonic diffraction patterns under the $x+x\to e$ with incident angles of -10°, 0°, and 10°; (d)-(e) represent the patterns under the $y+y\to e$ with incident angles of -10°, 0°, and 10°, respectively. The NCR and NRND are marked with boxes in (b) as an example. T=24°C and the pump power is 500 mW for all figures.
• Figure 3: Experimental and simulated nonlinear diffraction patterns for the $y+y\to e$ configuration at an incident angle of 0°. The crystal thickness $L_1$ is 1 mm, the distance from the crystal's surface B to the screen $L_2$ is 54.0 mm, and the poling period of the PPKTP crystal is 9.83 $\mu$m. (a) The grayscale distribution of Fig. \ref{['fig::5']}(e); (b) the projection of (a) on the horizontal axis; (c) the theoretical simulation result of (b).
• Figure 4: NCR and NRND patterns recorded in the PPKTP for the $y+y\to e$ configuration with a poling period of 9.83 $\mu$m at different temperatures: (a) T=24°C and (b) T=90°C. The pump power is 500 mW.
• Figure 5: NCR and NRND patterns generated using a PPKTP crystal with a poling period of 3.43 $\mu$m at an incident angle of 0°, for two different polarizations: (a) $x+x\to e$ and (b) $y+y\to e$. T=24°C and the pump power is 500 mW.