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E-O Crystal Properties

Electro-optic Pockels cells are used in applications that require fast switching of the polarization direction of a laser beam. These uses include Q-switching of laser cavities, coupling light into and out from regenerative amplifiers, conjunction with a pair of polarizers, light intensity modulation.
If a linearly polarized light passes through an E-O crystal, the phase retardation (G) will be induced by Dn to G = 2pDnL, where L is crystal length, for KD*P, again as an example, G = pLn3or63E/l. It is clear that the phase of light will change together with electric field (E). This is called electro-optic phase modulation. If two crossed polarizers are placed at input and output ends of E-O crystal separately, the output intensity of light will be I = I0sin2(G/2), where I0 is input intensity. That means the intensity or amplitude of light can also be modulated by electric field. This is called amplitude modulation.
longitudinal E-O modulation transverse E-O modulation
 
There are two kinds of E-O modulations. One is longitudinal E-O modulation if the directions of electric field and light propagation are the same. The KDP isomorphic crystals are normally used in this scheme. If the directions of electric field and light propagation are perpendicular, it is called transverse E-O modulation. The LiNbO3, MgO:LiNbO3, ZnO:LiNbO3, BBO and KTP crystals are usually employed in this scheme.
The half-wave voltage (Vp) is defined as the voltage at G = p, for example, Vp=l/(2no3r63) for KD*P and Vp=ld/(2no3r22L) for LiNbO3, where l is light wavelength and d is the distance between the electrodes.

EO Crystals Physical Properties
Crystals GTR-KTP BBO LiNbO3 DKDP RTP
Crystal stru. Orthorhombic Trigonal, Trigonal Tetragonal Orthorhombic,
Space group Pna21 R3c R3C   Pna21
Point group mm2   3m 42m Mm2
Cell parameters a=6.404Å,
b=10.616Å,
c=12.814Å,
Z=8		 a = b =
12.532 Å
c = 12.717Å
Z=6		 a=5.148Å   ,
c=13.863Å		   a = 12.96 Å
b= 10.56 Å
c =6.49 Å
Melt point 1172 ℃ 1095+ 5 ℃ 1253 ℃   ~ 1000 ℃
Curie point   925+ 5 ℃ 1140 ℃   ~810 ℃
Mohs hardness 5 4 5 2.5 ~5
Density 3.01 g/cm3 3.85 g/cm3 4.64 g/cm3 2.355 g/cm3 3.6 g/cm3
Thermal
expansion
coefficients: (/k)		   a,4 x 10-6 ;
c, 36 x 10-6		 //a2.0x10-6
//c16.7x10-6		 1.9x10-5 ⊥z
4.4x10-5 // z		 a1=1.01x10-6 ,
a2=1.37x10-6,
a3=-4.17x10-6
Hygroscopic
susceptibility		 No A Little No Yes No
Thermal
conductivity
W/m/K		 13 c, 1.2;
//c, 1.6		 38 1.9 ⊥z
2.1 // z		  
Therm-optic
coefficients:
(dn/dT, / C,)		 X:1.1x10-5
Y:1.3x10-5
Z:1.6x10-5		 o: -9.3 x 10-6
e:-16.6 x 10-6		 o: -0.874x10-6
e: 39.073x10-6		    

EO Crystals Optical Properties
Crystals KTP BBO LiNbO3 DKDP RTP
V 4x4x20mm ~1400V ~4800V ~950V ~3400V ~1400V
Contrast Ratio 20dB 40dB 25dB 30dB 20dB
Capacitance 5 pF <2pF 20 pF 7~10pF 6pF
Electrical Resistivity 1011-1012
W.cm		 1012-1013
W.cm		   109-1010
W.cm		 1011–1012
W.cm
Transmitting range(nm): 350 nm-4500 189-3500 420nm-5200 200-1600 350~4500
Electro-optic
coefficients:		 13 =9.5
23 =15.7
33 =36.3
42 =7.3
51 =9.3		 Y11 = 2.7
Y22, Y31 < 0.1 Y11		 YT33= 32,
YT31 =10 ,
YS31=8.6
YT22 = 6.8,
YS22=3.4		 r41=8.8pm/V
r63=25pm/V		 Y13=10.6
Y23=12.5
Y33=38.5
Ab.coef.@1064nm <50ppm <1000ppm <1000ppm <1000ppm <500ppm
Index @
1064nm		 nx=1.7377
ny=1.7453
nz=1.8297		 ne = 1.5425,
no = 1.6551		 ne = 2.156,
no = 2.232		 no=1.4948,ne
=1.4554		 nx=1.7424
ny=1.8211
nz=1.7905
damage threshold
(10 ns ):		 8J/cm^2 13J/cm^2 2J/cm^2 10J/cm^2 8J/cm^2