**8. Conclusion**

In summary, significant progress has been attained in the search for new, favorable IR nonlinear crystals, such as chalcogenides, chalcohalides, oxides, halides, and oxyhalides, for producing coherent energy in the MIR. For a good NLO crystal, the crystals must have good physical and chemical properties, such as wide transparency range, LDT, chemical stability, birefringence, and nonlinear susceptibility. Nevertheless, for practical applications, the crystals should have high qualities with promising properties. For promising optical applications, accurate optical properties should be measured. For MIR applications, high bandgap value, LDT, and NLO susceptibility optical transparency are important. Various IR crystals fulfill the basic conditions of IR-NLO applications. The significant behavior of these crystals recommends that this crystal can be used in different optical applications.

*Recent Advances in Infrared Nonlinear Optical Crystal DOI: http://dx.doi.org/10.5772/intechopen.108173*
