Nonlinear Optical Crystals: A Complete Survey

Materials chemistry and the pursuit of new compounds through exploratory synthesis are having a strong impact in many technological fields. The field of nonlinear optics is directly impacted by the availability of enabling materials with high performance. Nonlinear optical (NLO) phenomena such as second harmonic and difference frequency generation (SHG and DFG, respectively) are effective at producing a coherent laser beam in difficult to reach frequency regions of the electromagnetic spectrum. Such regions include the infrared (IR), far-infrared, and terahertz frequencies. High performance NLO crystals are critical for applications utilizing these coherent light sources, and new materials are continuously sought for better conversion efficiency and performance. The class of metal chalcogenides is the most promising source of potential NLO materials with desirable properties particularly in the IR region where most classes of materials face various fundamental challenges. We review the recent developments...

Metal Chalcogenides: A Rich Source of Nonlinear Optical Materials

Frequency down-conversion of solid-state laser sources to the mid-infrared spectral range using non-oxide nonlinear crystals

The new nonlinear optical (NLO) crystal BaGa4S7 for the mid-infrared (IR) has been grown by a Bridgman-Stockbarger technique. Polycrystalline materials with stoichiometric composition were synthesized from BaS, Ga, and S as the initial materials by solid-state reactions. The ultraviolet (UV) and IR transmittance of the crystal was determined with polished crystal pieces. The UV and IR optical absorption edges were found to be at 350 nm and 13.7 μm, respectively. From optical measurements of second harmonic generation on powders, the NLO coefficient d33 was determined to be 12.6 pm/V. The laser damage threshold of a single crystal reached about 1.2 J/cm2 at 1.064 μm. The Vickers-hardness value of the crystal is 327.5 HV5, which is equivalent to Mohs’ hardness of about 5.

Growth and Characterization of BaGa4S7: A New Crystal for Mid-IR Nonlinear Optics

The family of metal thiophosphates is an important but long-ignored compound system of the nonlinear optical (NLO) materials with desirable properties for the mid-infrared (mid-IR) coherent light generation. In the present work, the mid-IR NLO capabilities of metal thiophosphate crystals are systematically investigated based on their structure-property relationship. The linear and nonlinear optical properties of these crystals are predicted and analyzed using the first-principles calculations. In particular, several metal thiophosphate compounds are highlighted to exhibit good mid-IR NLO performances, as supported by the primary experimental results. These candidates would greatly promote the development of the mid-IR NLO functional materials.

Metal Thiophosphates with Good Mid-infrared Nonlinear Optical Performances: A First-Principles Prediction and Analysis

Single crystals LiGaX 2 (X = S, Se, Te) of optical quality were grown, with transparency ranges at 5 cm -1 absorption level of 0.32-11.6 μm, 0.37-13.2 μm and 0.54-14.2 μm, respectively. The first two, LiGaS 2 and LiGaSe 2 , have a wurtzite-type structure whereas LiGaTe 2 is tetragonal (chalcopyrite lattice). The three refractive indices were measured in the whole transparency ranges of LiGaS 2 and LiGaSe 2 and n a and n c were found to be very close (quasi-uniaxial optical anisotropy) with a crosspoint at 6.5 μm (LiGaS 2 ) and 8 μm (LiGaSe 2 ). Sellmeier equations were fitted and phase-matching conditions for second harmonic generation (SHG) were calculated: the 1.467-11.72 μm spectral range for the fundamental is covered by LiGaS 2 and LiGaSe 2 .

Growth and properties of LiGaX2 (X = S, Se, Te) single crystals for nonlinear optical applications in the mid-IR

Growth of new nonlinear crystals LiMX2 (M = Al, In, Ga; X = S, Se, Te) for the mid-IR optics

By second harmonic generation in and out of the principal planes we estimated the three nonlinear coefficients of the Li-containing mid-IR crystals LiGaS2 and LiGaSe2 which are isostructural to LiInS2 and LiInSe2 and possess even larger bandgaps First results on optical parametric amplification reveal their advantages for direct down conversion to the mid-IR

Second harmonic generation and optical parametric amplification in the mid-IR with orthorhombic biaxial crystals LiGaS2 and LiGaSe2

We review on the growth improvement and optical characterization of a new family of ternary lithium-based chalcogenide crystals of generic formula LiB III C 2 VI (B = In, Ga; C = S, Se, Te) which displays improved thermo-mechanical properties for mid-IR nonlinear optical applications. Some of these compounds are now produced in sufficiently large size, single-domain quality to allow their implementation in optical parametric oscillators.

Ternary chalcogenides LiBC2 (B = In, Ga; C = S, Se, Te) for mid-IR nonlinear optics

Single crystals of lithium selenoindate (LiInSe2) are grown by the Bridgman–Stockbarger technique up to sizes of 10 mm in diameter and 20 mm in length. The different phases have color from yellow (as grown) to dark red (after annealing) but all have the same wurtzite type structure mm2 with slightly differing cell parameters. The band gap for the yellow phase at 300 K is at 2.86–2.87 eV. The red color is attributed to point defects and can be removed by proper illumination. Sellmeier equations are constructed for the 0.5–11 μm range and their validity is checked with second harmonic generation which provides first estimations of the nonlinear coefficients of LiInSe2. The potential of LiInSe2 is compared to that of the widely spread and technologically mature AgGaS2.

Sergei Lobanov

Papers

Growth and properties of LiGaX2 (X = S, Se, Te) single crystals for nonlinear optical applications in the mid-IR

Growth of new nonlinear crystals LiMX2 (M = Al, In, Ga; X = S, Se, Te) for the mid-IR optics

Second harmonic generation and optical parametric amplification in the mid-IR with orthorhombic biaxial crystals LiGaS2 and LiGaSe2

Ternary chalcogenides LiBC2 (B = In, Ga; C = S, Se, Te) for mid-IR nonlinear optics

LiInSe2: A biaxial ternary chalcogenide crystal for nonlinear optical applications in the midinfrared