Ultrathin BBO for Ultrafast Lasers

For frequency conversions of ultrafast lasers, one of the main concerns is pulse broadening induced by group velocity (Vg) mismatch between the input pulse(s) and the generated pulse in an NLO crystal. In order to avoid pulse broadening, the thickness of the crystal should not exceed the maximum length (Lmax) as defined by the pulsewidth divided by the inversed group velocity mismatch (IGVM = ΔVg-1). The table below lists the Lmax for second harmonic generation (SHG) and sum frequency generation (SFG) of 10 fs pulses at the wavelength range of a Ti:Sapphire laser, the most popular ultrafast laser.

Type I PM in BBO Crystals	SHG @ 700 nm	SHG @ 800 nm	SHG @ 900 nm	SFG @ 700 nm + 350nm	SFG @ 800 nm + 400 nm	SFG @ 900 nm + 450nm
IGVM (ps/cm)	2.72	1.92	1.40	8.50	5.68	4.08
Lmax @ 10fs (µm)	40	50	70	10	18	25

Apparently a thickness of sub-100 µm (0.1 mm) is desired for all the frequency conversion processes of 10fs pulses. In particular, crystals as thin as 10-20 µm may be needed for generation of very short UV wavelengths below 300nm.

Newlight Photonics Inc. can provide BBO crystals as thin as 10 µm (0.01 mm) for frequency conversions of ultrafast pulses.

We also supply birefringent calcite plates and alpha-BBO plates for compensation of temporal walkoff in nonlinear crystals (time delay compensators), please contact us for details.

Standard Products

Part No.	Width x Height x Thickness	Coating	Application
BTC2511	5 x 5 x 0.01 mm	P-coating	SHG @ 800 nm
BTC2512	5 x 5 x 0.02 mm	P-coating	SHG @ 800 nm
BTC2515	5 x 5 x 0.05 mm	AR@800/400nm or P-coating	SHG @ 800 nm
BTC2521	5 x 5 x 0.1 mm	AR@800/400nm or P-coating	SHG @ 800 nm
BTC2522	5 x 5 x 0.2 mm	AR@800/400nm or P-coating	SHG @ 800 nm
BTC2525	5 x 5 x 0.5 mm	AR@800/400nm or P-coating	SHG @ 800 nm
BTC2531	5 x 5 x 1.0 mm	AR@800/400nm or P-coating	SHG @ 800 nm
BTC2532	5 x 5 x 2.0 mm	AR@800/400nm or P-coating	SHG @ 800 nm
BTC3511	5 x 5 x 0.01 mm	P-coating	SFG @ 800nm + 400nm
BTC3512	5 x 5 x 0.02 mm	P-coating	SFG @ 800nm + 400nm
BTC3515	5 x 5 x 0.05 mm	AR@800/400/267nm or P-coating	SFG @ 800nm + 400nm
BTC3521	5 x 5 x 0.1 mm	AR@800/400/267nm or P-coating	SFG @ 800nm + 400nm
BTC3525	5 x 5 x 0.5 mm	AR@800/400/267nm or P-coating	SFG @ 800nm + 400nm
BTC3531	5 x 5 x 1.0 mm	AR@800/400/267nm or P-coating	SFG @ 800nm + 400nm
BTC3532	5 x 5 x 2.0 mm	AR@800/400/267nm or P-coating	SFG @ 800nm + 400nm

Coatings

Protective coating (P-coating): This is a single-layer MgF2 coating. The primary function of the P-coating is to "protect" polished BBO surfaces from fogging due to ambient moisture. The protective coating can also partially reduces reflection from polished surface at a certain wavelength range.

Anti-reflective coating (AR coating): This is a multi-layer dielectric coating. Single-band, dual-band or broad-band AR coatings on BBO surfaces are available for different applications.

Substrate

Crystals of thickness 50µm (0.05mm) or thinner are supplied optically contacted on UV fused silica substrates with a typical thickness of 2.0mm. Ultrafast pulses should be incident on the crystal side.

Mount

For customer convenience and protection of ultrathin crystals, all ultrathin crystals are pre-mounted in a 1" ( 25.4 mm ) anodized aluminum (Al) holder. The orientation of a mounted crystal can be seen here. A standard 1" mirror mount may be conveniently used to tune the crystals for optimized frequency conversions.
( Mirror mount and post are not included)

Specifications on finished ultrathin BBO

Wavefront distortion:	less than λ/8 @ 633 nm
Clear aperture:	> 90% central area
Flatness:	λ/8 @ 633 nm
Surface quality:	10/5 Scratch/Dig per MIL-O-13830A
Parallelism:	better than 20 arc seconds
Perpendicularity:	15 arc minutes
Angle tolerance:	Δθ < 0.25o, Δφ < 0.25o