Phase-Matching Properties at around 190 nm of Various Borate Crystals

Abstract

We report on the phase-matching properties of borate crystals of LiB3O5 (LBO), CsB3O5 (CBO), and CsLiB6O10 (CLBO) in vacuum–ultraviolet (VUV) light generation at around 190 nm. A new phase-matching property in the VUV spectral range for CBO grown from a self-flux solution was found to have better agreement with new Sellmeier's equations developed in our laboratory. A 189 nm output of 11.4 mW was produced in a CLBO with a conversion efficiency of 7.3% from 213 nm input. CLBO is suitable for VUV light generation around 190 nm with the present laser system.

179 nm Generation with borate crystal

“…On the other hand, there was no SFG obtained at around 180 nm with CBO, which contradicted the theoretical prediction based on Sellmeier's equations [3]. As deviation of phase-matching angle from theoretical value was observed in 190 nm generation, we thought such deviation could become remarkable in 180 nm range.…”

“…The 198 nm light generated with β-BaB 2 O 4 (BBO) is now implemented in the leading-edge photomask inspection equipment [1,2]. In order to develop laser source under 190 nm, we built solid-state laser system for 189 nm and successfully generated 11.4 mW output with CsLiB 6 O 10 (CLBO) [3]. Borate crystals were widely used as nonlinear frequency conversion material in such research as they have properties of large nonlinear coefficients and short absorption edges.…”

“…For commercial applications, borate crystals such as LiB 3 O 5 (LBO) and CLBO are still favored since they had been launched into mass production. As the phase-matching angles at 179 nm for LBO and at 180 nm for CB 3 O 5 (CBO) were calculated as shown in Table 1, they were found to have the potential in such generation [3,5]. We thought out a new scheme for 179 nm (180 nm) generation, which is achieved by sum-frequencygeneration (SFG) in LBO with 198.8 nm deep-ultraviolet (DUV) and infrared (IR) at about 1800 nm.…”

VUV Light Generation with CLB6O10 and LB3O5

“…The measured type I phase-matching angles of φ for LBO in the xy plane and θ for CLBO are in good agreement with the theoretical curves calculated from Sellmeier's equations. A maximum output of 11.4 mW for VUV at 189.1 nm was achieved with a 15-mm length CLBO [1]. It is expected to generate VUV until 185 nm in CLBO without serious absorption from the experimental results as shown in Fig.1.…”

Refined Sellmeier and thermo-optic dispersion formulas for Li2B4O7

“…A high-power deep-UV laser source based on nonlinear optical frequency conversion is important for medical and industrial applications owing to its compactness and it being maintenance-free. In fact, many papers on deep-UV generation in borate crystals such as KB 5 O 8 1 4H 2 O (KB5), [1][2][3] β-BaB 2 O 4 ( β-BBO), [4][5][6] LiB 3 O 5 (LBO), [7][8][9][10] CsB 3 O 5 (CBO), [9][10][11][12] CsLiB 6 O 10 (CLBO), 9,[13][14][15][16][17][18] K 2 Al 2 B 2 O 7 (KABO), 19) and KBe 2 BO 3 F 2 (KBBF) 20,21) have been reported. Owing to its adequate birefringence and high damage threshold, Li 2 B 4 O 7 was also found to be a promising material for deep-UV generation using a solid-state laser with emission at 1 µm.…”