LBO Crystal

LBO (Lithium Triborate - LiB3O5) is now the most popularly used material for Second Harmonic Generation (SHG) of 1064nm high power lasers (as a substitute to KTP) and Sum Frequency Generation (SFG) of 1064nm laser source to achieve UV light at 355nm.

LBO is phase matchable for the SHG and THG of Nd:YAG and Nd:YLF lasers, using either type I or type II interaction. For the SHG at room temperature, type I phase matching can be reached and has the maximum effective SHG coefficient in the principal XY and XZ planes in a wide wavelength range from 551nm to about 2600nm. SHG conversion efficiencies of more than 70% for pulse and 30% for cw Nd:YAG lasers, and THG conversion efficiency over 60% for pulse Nd:YAG laser have been observed.LBO is an excellent NLO crystal for OPOs and OPAs with a widely tunable wavelength range and high powers. These OPO and OPA which are pumped by the SHG and THG of Nd:YAG laser and XeCl excimer laser at 308nm have been reported. The unique properties of type I and type II phase matching as well as the NCPM  leave a large room in the research and applications of LBO's OPO and OPA.

Advantages:

• Broad transparency range from 160nm to 2600nm ;

• High optical homogeneity (δn≈10-6/cm) and being free of inclusion;

• Relatively large effective SHG coefficient (about three times that of KDP);

• High damage threshold;• Wide acceptance angle and small walk-off;

• Type I and type II non-critical phase matching (NCPM) in a wide wavelength range;

• Spectral NCPM near 1300nm.

Applications:

• More than 480mW output at 395nm is generated by frequency doubling a 2W mode-locked Ti:Sapphire  laser (<2ps, 82MHz). The wavelength range of  700-900nm is covered by a 5x3x8mm3 LBO crystal.

• Over 80W green output is obtained by SHG of a Q-switched Nd:YAG laser in a type II 18mm long LBO crystal.

• The frequency doubling of a diode pumped Nd:YLF laser (>500μJ @ 1047nm,<7ns, 0-10KHz) reaches over 40% conversion efficiency in a 9mm long LBO crystal.

• The VUV output at 187.7 nm is obtained by sum-frequency generation.

• 2mJ/pulse diffraction-limited beam at 355nm is obtained by intracavity frequency tripling a Q-switched Nd:YAG laser.

•  A quite high overall conversion efficiency and 540-1030nm tunable wavelength range were obtained with OPO pumped at 355nm.

• Type I OPA pumped at 355nm with the pump-to-signal energy conversion efficiency of 30% has been reported.

• Type II NCPM OPO pumped by a XeCl excimer laser at 308nm has achieved 16.5% conversion efficiency, and moderate tunable wavelength ranges can be obtained with different pumping sources and temperature tuning.

• By using the NCPM technique, type I OPA pumped by the SHG of a Nd:YAG laser at 532nm was also observed to cover a wide tunable range from 750nm to 1800nm by temperature tuning from 106.5℃ to 148.5℃.

• By using type II NCPM LBO as an optical parametric generator (OPG) and type I critical phase-matched BBO as an OPA, a narrow linewidth (0.15nm) and high pump-to-signal energy conversion efficiency (32.7%) were obtained when it is pumped by a 4.8mJ, 30ps laser at 354.7nm. Wavelength tuning range from 482.6nm to 415.9nm was covered either by increasing the temperature of LBO or by rotating BBO.