ZnGeP2（Zinc germanium phosphide）crystal has many good properties and is an mid-IR nonlinear crystal. The nonlinear susceptibility of ZnGeP2 (ZGP) crystal is approximately 160 times large (d36~75 pm/V) as KDP,.ZGP shows good optical transparency over the 0.74–12 mm and relatively high laser damage threshold, and is therefore well suited for producing near infrared tunable laser. ZGP is a very hopeful material for mid-infrared devices such as SHG, SFG, OPO, and OPG/OPA.
Chemical and Physical properties
| Property | Value |
| Chemical Formula | ZnGeP2 |
| Crystal Structure | Tetragonal,`42m |
| Lattice Parameter | a=b=5.467Å, c=12.736Å |
| Mass Density | 4.16 g/cm3 |
| Moh Hardness | 5.5 |
| Melting Point | About 1040°C |
| Thermal Conductivity | 180 W/m/K |
| Thermal Expansion Coefficient | β‖,5×10-6/K; β⊥,7.8×10-6/K |
| Birefringence | positive uniaxial |
| Property | Value |
| Transparency Range | 0.74 – 12 um |
| Absorption Coefficient | α<0.05cm-1 @2050-2100 nm |
| Refractive Indices | |
| @ 2.05 um | no = 3.1478, ne = 3.1891 |
| @ 2.79 um | no = 3.1333, ne = 3.1744 |
| @ 5.30 um | no = 3.1136, ne = 3.1547 |
| @ 10.6 um | no = 3.0729, ne = 3.1143 |
| Sellmeier Equations(λ in μm) | no2(λ) = 4.64467+5.10087/(λ2-0.13656)+4.27777λ2/(λ2-1653.89) |
| ne2(λ) = 4.71539+5.26358/(λ2-0.14386)+2.37310λ2/(λ2-1000.82) | |
| Property | Value |
| SHG Phase Matchable Range | 3177 ∼ 10357nm (Type I) |
| NLO coefficients | d36=75 ± 8 pm/V |
| Type Ⅰ deeo=d36 sin2θcos2φ | |
| Type Ⅱ doeo=deoo=d36 sinθsin2φ | |
| Damage Threshold | |
| at 2.79 um | 30 GW/cm2 (150 ps) |
| at 10.6 um | 1 GW/cm2 (2 ns) |
| λ[µm] | α [cm-1] | Note |
| 1.064 | 1.52 | |
| 1.06 | best crystals | |
| 1.9 | 0.8–0.95 | |
| 2 | 0.15 | o-wave, best crystals |
| 0.16 | ||
| 2.05 | 0.35 | |
| 0.26 | o-wave | |
| 0.23 | ||
| 0.2 | o-wave, after annealing | |
| <0.1 | best crystals | |
| 0.09 | best crystals | |
| 0.02–0.04 | after annealing and radiation processing | |
| 2.08 | 0.62 | o-wave, mean value |
| 1.2 | e-wave, mean value | |
| 2.15 | 0.6 | |
| 0.09–0.25 | typical crystals, o-wave | |
| 0.03 | best crystals, o-wave | |
| 2.39 | 0.55 | |
| 2.5 | 0.11 | o-wave, as-grown crystals |
| 2.5–8 | <0.1 | |
| 2.5–8.3 | <0.2 | |
| 2.5–8.5 | <0.1 | |
| 2.73 | 0.03 | |
| 2.75 | 0.3 | |
| 2.79 | 0.06 | |
| 2.8 | 0.01 | best crystals, o-wave |
| 2.8–8.3 | <0.1 | |
| 3–8 | 0.005–0.15 | |
| <0.1 | ||
| <0.01 | ||
| 3.15 | 0.17 | |
| 3.5–3.9 | 0.41 | o-wave, SFG direction |
| 3.5 | 0.4 | |
| 3.8 | 0.1–0.18 | |
| 3.9–4.5 | 0.1 | |
| 4–8.5 | <0.05 | |
| 4.5–8 | 0.03 | best samples |
| 4.65 | 0.4 | |
| 0.1–0.2 | ||
| 0.01–0.05 | SHG direction | |
| 4.78 | <0.055 | |
| 0.16 | ||
| 5.3–6.1 | 0.32 | e-wave, SFG direction |
| 5.5–6.3 | 0.1 | |
| 7.8 | 0.15 | |
| 8.24 | 0.02 | |
| 8.3 | 0.45 | |
| 8.3–9.5 | <0.3 | |
| 9 | 0.9 | |
| 9.2 | 0.51 | |
| 9.28 | 0.4 | |
| 9.3 | 0.8 | |
| 0.7 | SHG direction | |
| 0.4–0.5 | ||
| 0.48 | e-wave | |
| 9.5 | 0.39 | e-wave |
| 9.55 | 0.26 | SHG direction |
| 0.56 | ||
| 9.6 | 0.33 | |
| 9.7 | 0.33 | e-wave |
| 10 | 0.45 | |
| 10.3 | 0.42 | |
| 10.4 | 0.6 | |
| 10.6 | 0.9 | |
| 0.83 | e-wave, SFG direction | |
| 0.65 | ||
| 10.7 | 0.88 | e-wave |
| 11.1 | 1.2 |
Experimental Values of Refractive Indices
| λ[µm] | no | ne | λ[µm] | no | ne |
| 0.64 | 3.5052 | 3.5802 | 3.40 | 3.1263 | 3.1647 |
| 0.66 | 3.4756 | 3.5467 | 3.60 | 3.1257 | 3.1632 |
| 0.68 | 3.4477 | 3.5160 | 3.80 | 3.1237 | 3.1616 |
| 0.70 | 3.4233 | 3.4885 | 4.00 | 3.1223 | 3.1608 |
| 0.75 | 3.3730 | 3.4324 | 4.20 | 3.1209 | 3.1595 |
| 0.80 | 0.80 | 3.3915 | 4.50 | 3.1186 | 3.1561 |
| 0.85 | 3.3063 | 3.3593 | 4.70 | 3.1174 | 3.1549 |
| 0.90 | 3.2830 | 3.3336 | 5.00 | 3.1149 | 3.1533 |
| 0.95 | 3.2638 | 3.3124 | 5.50 | 3.1131 | 3.1518 |
| 1.00 | 3.2478 | 3.2954 | 6.00 | 3.1101 | 3.1480 |
| 1.10 | 3.2232 | 3.2688 | 6.50 | 3.1057 | 3.1445 |
| 1.20 | 3.2054 | 3.2493 | 7.00 | 3.1040 | 3.1420 |
| 1.30 | 3.1924 | 3.2346 | 7.50 | 3.0994 | 3.1378 |
| 1.40 | 3.1820 | 3.2244 | 8.00 | 3.0961 | 3.1350 |
| 1.60 | 3.1666 | 3.2077 | 8.50 | 3.0919 | 3.1311 |
| 1.80 | 3.1562 | 3.1965 | 9.00 | 3.0880 | 3.1272 |
| 2.00 | 3.1490 | 3.1889 | 9.50 | 3.0836 | 3.1231 |
| 2.20 | 3.1433 | 3.1829 | 3.1829 | 3.0788 | 3.1183 |
| 2.40 | 3.1388 | 3.1780 | 10.50 | 3.0738 | 3.1137 |
| 2.60 | 3.1357 | 3.1745 | 11.00 | 3.0689 | 3.1087 |
| 3.00 | 3.1304 | 3.1693 | 12.00 | 3.0552 | 3.0949 |
| 3.20 | 3.1284 | 3.1671 |
Experimental Values of Phase-matching Angle (T =293K)
| Interacting wavelengths[μm] | θexp [deg] |
| SHG, e+e⇒o | |
| 3.9278⇒1.9639 | 57.8±0.3 |
| 4.34⇒2.17 | 55.8±0.2 |
| 4.64⇒2.32 | 47.5 |
| 4.775⇒2.3875 | 49.2 |
| 5.2955⇒2.64775 | 46.8 |
| 9.2⇒4.6 | 63.8 |
| 9.3054⇒4.6527 | 61.3/63/64 |
| 9.5⇒4.75 | 62.1/66.8 |
| 9.5524⇒4.7762 | 65.3 |
| 9.6036⇒4.8018 | 64.9/65.8 |
| 10.2⇒5.1 | 72 |
| 10.3035⇒5.15175 | 74.3/74.5 |
| 10.5514⇒5.2757 | 79.2 |
| 10.5910⇒5.2955 | 80.1 |
| SFG, e+e ⇒ o | |
| 10.668+4.34⇒3.085 | 54.3±0.2 |
| 10.5910+5.2955⇒3.53033 | 52.1 |
| 10.5910+3.53033⇒2.64775 | 48.4 |
| 9.74+4.2039⇒2.9365 | 49.6 |
| 5.2955+3.53033⇒2.1182 | 51.7 |
| SFG, o+e ⇒ o | |
| 6.74+5.2036⇒2.9365 | 76 |
| 6.45+5.3908⇒2.9365 | 79.2 |
| 6.25+5.5389⇒2.9365 | 84 |
| 6.15+5.6199⇒2.9365 | 85.5 |
| 6.29+5.0173⇒2.791 | 76 |
| 6.19+5.0828⇒2.791 | 77.6 |
| 6.06+5.1739⇒2.791 | 80.5 |
| 6.015+5.207⇒2.791 | 84 |
| 5.95+5.2569⇒2.791 | 83.4 |
| 5.90+5.2965⇒2.791 | 87 |
| 10.5910+1.0642⇒0.96703 | 84 |
Experimental Values of Internal Angular Bandwidth
| Interacting wavelengths[μm] | Δθint [deg] |
| SHG, e+e ⇒ o | |
| 3.8⇒1.9 | 1.33 |
| 4.34⇒2.17 | 1.05 |
| 5.3⇒2.65 | 0.69 |
| 7.8⇒3.9 | 0.5 |
| 9.3⇒4.65 | 0.74–0.80 |
| 0.83 | |
| 1.15 | |
| 9.55⇒4.775 | 0.89 |
| 9.6⇒4.8 | 0.8 |
| 10.2⇒5.1 | 1.35 |
| 10.3⇒5.15 | 1.2 |
| SFG, e+e ⇒ o | |
| 10.668+4.34⇒3.085 | 1.23 |
| SFG, o+e ⇒ o | |
| 10.6+1.064⇒0.967 | 0.55 |
Temperature Variation of Phase-matching Angle
| Interacting wavelengths [μm] | dθpm/dT [deg/K] |
| SHG, e+e ⇒ o | |
| 9.2⇒4.6 | 0.014 |
| 10.3⇒5.15 | 0.072 |
| 10.6⇒5.3 | 0.107 |
| SFG, o+e ⇒ o | |
| 10.6+1.0642⇒0.9671 | 0.007 |
Laser-induced Surface-damage Threshold
| λ[µm] | τp [ns] | Ithr[GW/cm2] | Note |
| 1.0642 | 30 | >0.003 | 12.5Hz |
| 10 | 0.003 | ||
| 1.3 | 0.00013 | >150 | 1kHz |
| 1.66 | 0.00013 | >100 | 1kHz |
| 2.05 | 30 | 0.013–0.016 | 5kHz |
| 10 | >0.074 | 10kHz | |
| 2.79 | 50 | >0.014 | 10Hz |
| 0.018 | 10Hz | ||
| 0.15 | 30 | ||
| 0.1 | 35 | 1Hz | |
| 2.8 | 70 | 0.056 | 1Hz, uncoated sample |
| 1Hz, coated samples | |||
| 0.08 | |||
| 2.94 | 0.11 | 30 | |
| 5.3–6.1 | CW | >0.00001 | |
| 0.00025 | |||
| 7.8 | 5000 | 10 | |
| 9.2–10.8 | CW | >0.00008 | |
| 9.28 | 2 | 1.25 | |
| 9.3 | 100 | 0.012 | 100Hz |
| 50 | >0.06 | 1Hz | |
| 9.3–10.6 | 125 | 0.025 | 20Hz |
| 0.03–0.04 | 2Hz | ||
| 9.55 | 220 | 0.078 | |
| 30 | 0.14 | SHG direction | |
| 10.2–10.8 | CW | >0.000001 | |
| 100,000–10,000,000 | 0.06 | 1500Hz | |
| 10.6 | CW | >0.00000001 | |
| 0.0002 |
Experimental Values of Spectral Bandwidth and Temperature Bandwidth
| Experimental Values of Spectral Bandwidth | ||
| Interacting wavelengths[μm] | Δν[cm-1] | |
| SHG, e+e ⇒ o | ||
| 4.34⇒2.17 | 7.9 | |
| 10.2⇒5.1 | 4.9 | |
| Experimental Values of Temperature Bandwidth | ||
| Interacting wavelengths[μm] | θexp[deg] | ΔT[℃] |
| SHG, e+e ⇒ o | ||
| 10.5910⇒5.2955 | 80.1 | 44 |
| 10.3035⇒5.15175 | 74.5 | 45 |
| 10.2⇒5.1 | 72 | 50 |
| 9.6036⇒4.8018 | 65.8 | 48 |
| SFG, o+e ⇒ o | ||
| 10.5910+1.0642⇒0.96703 | 84 | 81.9 |
| Linear Thermal Expansion Coefficient αt | ||
| ΔT [K] | αt×106[K-1], ||c | αt×106[K-1], ⊥c |
| 293–573 | 15.9 | 17.5 |
| 573–873 | 8.08 | 9.1 |
| Thermal Conductivity Coefficient κ： | ||
| T [K] | κ[W/mK], ||c | κ[W/mK], ⊥c |
| 293 | 36 | 35 |
| Two-photon Absorption Coefficient β | ||
| λ[μm] | τp[ns] | β×1011 |
| 1.3 | 0.00013 | 25 |
| Linear Electrooptic Coefficients Measured at High Frequencies(well above the acoustic resonances of ZnGeP2 crystal,i.e.,for the “clamped” crystal)at Room Temperature: | ||
| λ[µm] | r41S[pm/V] | r63S[pm/V] |
| 3.3913 | 1.6 | -0.8 |
Nonlinear coefficient is large
The region of transmission is from 0.74 um to 12um
High relative damage threshold
High thermal conductivity
The region of transparency is wide
Phase matching over a broad spectral region
Producing coherent radiation in sub-millimeter-range from 70.0 μm to 1000 μm - terahertz range
Combining frequencies of CO2- and CO-lasers radiation or other lasers that working in the transparency region of ZGP
SHG of CO-laser
Second, third, and fourth harmonic generation of CO2 laser
OPO(Optical parametric generation) with pumping at wavelengths of 2.05-2.94 μm and possibility to generate effectively 3-10 μm ranges