KDP/KD*P Crystals

Characterized by the excelent UV transmission, high damage threshold, and high birefringence, KDP (Potassium Dihydrogen Phosphate) and KD*P (Potassium Dideuterium Phosphate) are useful commercial NLO materials for doubling, tripling and quadrupling of Nd:YAG laser at room temperature or an elevated temperature. They are also excellent electro-optic (EO) crystals with high electro-optic coefficients, widely used as electro-optical modulators and Pockels cells for Q-switched lasers. One disadvantage of KDP/KD*P crystals is that they are highly hygroscopic, therefore, protective coating or a sealed housing with transmitting windows is recommended for protection of polished crystal faces.

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Part No.	Description	Application	Material	Wavelength	Bandwidth	Size	Aperture	Thickness	Length	Angle	Doping	Orientation	Displacement	Retardation	Delay	Coating	End cut	Holder	Price	Availability	Add to Cart

Basic Physical and Optical Properties:

	KDP	KD*P(DKDP)
Chemical Formula	KH₂PO4	KD₂PO₄
Crystal Structure	Tetragonal	Tetragonal
Transmission Range	200-1500 nm	200-1600 nm
Nonlinear Coefficients	d36=0.44 pm/V	d36=0.40 pm/V
Refractive Indices (at 1064 nm)	no=1.4938, ne=1.4599	no=1.4948, ne=1.4554
Electro-Optical Coefficients	r41=8.8 pm/V r63=10.3 pm/V	r41=8.8 pm/V r63=25 pm/V
Mohs Hardness	2.5	2.5
Surface Damage Threshold (@10 Hz, 10 ns, 1064 nm )	0.5 GW/cm²	0.5 GW/cm²
Sellmeier Equations of KDP (λ in µm)	no² = 2.259276 + 13.005522λ²/(λ² - 400)+ 0.01008956/(λ² - 0.012942625) ne² = 2.132668 +3.2279924λ2/(λ² - 400) + 0.008637494/(λ²- 0.012281043)
Sellmeier Equations of KD*P (λ in µm)	no² = 2.240921 + 2.246956λ²/(λ² -126.92073)+ 0.009676/(λ² - 0.0156203) ne² = 2.126019 + 0.784404λ²/(λ² - 123.40344) + 0.008578/(λ²- 0.0119913)

Cut Orientations for KDP/KD*P Crystal

Process (PM type)	KDP		KD*P
Process (PM type)	Orientation	Deff(pm/V)	Orientation	Deff(pm/V)
SHG (II): 1064 nm -> 532 nm	58.9	0.34	53.5°	0.34
THG (II): 1064+532 -> 355 nm	58.4	0.37	59.4°	0.33
SFG (II): 1064+(421-1000 nm) -> 302-515 nm	61.0	0.36	63.7°	0.31
FHG (I): 532 nm -> 266 nm	76.7	0.46	85.9°	0.43
NCPM FHG (I): 532 -> 266 nm	90°(T=250°C)	0.47	90°(T=55°C)	0.43
SHG (I): 1064 nm -> 532 nm	41.1	0.26	36.6°	0.22
THG(I): 1064+532 -> 355 nm	47.4	0.32	46.8°	0.29

Specifications on finished crystals:

Wavefront distortion:	less than λ/8 @ 633 nm
Dimension tolerance:	(W ± 0.1 mm) x (H ± 0.1 mm) x (L + 0.2/-0.1 mm)
Clear aperture:	> 90% central area
Flatness:	λ/8 @ 633 nm
Surface Quality:	Scratch/Dig 10/5 per MIL-O-13830A
Parallelism:	better than 20 arc seconds
Perpendicularity:	5 arc minutes
Angle tolerance:	Δθ < +/-0.5 deg, Δφ < +/-0.5 deg

Crystal Handling:

KDP, KD*P are highly hygroscopic and have to be used/stored in a very dry environment. A small enclosure (with openings for light) may be built around the crystal with a continuous flow of dry nitrogen or air into the enclosure. The dry nitrogen/air pressure needs only to be slightly above the atmosphere to keep the small volume around the crystal dry and clean.

Coating:

Single layer protective coating or anti-reflection coatings are available upon request.

Uncoated crystals can also be housed in a sealed housing with AR coated windows (shown at the right).

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