BBO crystal (β-Barium Borate, β-BaB?O?), a trigonal non-centrosymmetric nonlinear optical crystal, is renowned for generating 2nd–5th harmonics of Nd:YAG lasers with efficiencies up to 70% (SHG, 532 nm), 60% (THG, 355 nm), 50% (FHG, 266 nm), and a record 200 mW at 213 nm (FFHG). Its superior performance stems from a broad transparency range (189–3500 nm), high nonlinear coefficient (d?? = 2.6 pm/V at 1064 nm→532 nm), low photorefractivity, and non-hygroscopicity, making it critical for UV lithography, laser micromachining, and medical optics.

KTP crystal is mostly used as nonlinear crystals for frequency doubling of solid-state Nd:YAG crystal or Nd:YVO4 crystal laser, as it has large nonlinear optical coefficients, wide angular bandwidth and small walk-off angle, broad temperature and spectral bandwidth. KTP crystal also has high electro-optic(E-O) coefficient and low dielectric constant, and large figure of merit, these features make it also widely used in electro-optic application.

Periodically Poled Potassium Titanyl Phosphate (PPKTP) crystal is a ferroelectric nonlinear crystal with a unique structure, which aids in efficient frequency conversion through Quasi - Phase - Matching (QPM). The crystal is composed of alternating domains with spontaneous polarization of opposite orientations, enabling QPM to correct the phase mismatch in nonlinear interactions. The crystal is suitable for efficient conversion of any nonlinear process within its transparency range.

LBO Crystal, short for Lithium Triborate Crystal, is a remarkable nonlinear optical crystal. With a chemical formula of LiB?O?, it features a wide transparency range from 155 to 3200 nm, allowing interaction with diverse laser sources. It has a high damage threshold, capable of withstanding intense laser beams without performance degradation, which is crucial for high - power laser applications. LBO Crystal also shows excellent optical homogeneity. It's widely used in frequency doubling, tripling of high - peak - power pulsed lasers, and optical parametric oscillators. Its outstanding properties make it an essential component in optical systems like medical lasers, laser displays, and optical data storage.

Lithium Niobate (LiNbO3) is widely used as electro-optic modulator and Q-switch for Nd:YAG, Nd:YLF and Ti:Sapphire lasers as well as modulator for fiber optics, etc. The transverse modulation is mostly employed for LiNbO3 crystal. Also LiNbO3 Crystal is widely used as frequency doublers for wavelength >1um and optical parametric oscillators (OPO) pumped at 1064 nm as well as quasi-phase-matched (QPM) devices.

Potassium Dihydrogen Phosphate (KDP, KH?PO?) and Potassium Dideuterium Phosphate (KDP, KD?PO?) are tetragonal nonlinear optical crystals widely used for second (532 nm, 60% efficiency), third (355 nm), and fourth harmonic generation (266 nm) of Nd:YAG lasers via type I/II phase matching at room temperature, with KDP offering 75% SHG efficiency and higher damage threshold via deuteration. As electro-optic materials, they feature ultra-high coefficients (r??=23.3 pm/V for KDP), low half-wave voltage (~7.6 kV at 1064 nm), and broad bandwidth (>10 GHz), enabling applications in Pockels cells, modulators, and high-power laser systems like inertial confinement fusion, where KDP’s non-hygroscopicity outperforms KDP in harsh environments.

Based on the quasi - phase matching theory (QPM), when the nonlinear optical crystal lithium niobate (LN) is fabricated into a periodically reversed domain structure, it is called a periodically poled lithium niobate crystal (PPLN). This structure can compensate for the phase mismatch caused by dispersion, thereby maximizing the utilization of the effective nonlinear coefficient of the nonlinear optical crystal and significantly enhancing the frequency conversion characteristics of the nonlinear crystal.

Calcite (CaCO?), a trigonal negative uniaxial crystal with extreme birefringence and broad transmission (200 nm–2300nm), is the premier material for visible-near infrared polarizing optics despite its softness (Mohs 3) and hygroscopicity. It enables Glan–Taylor/Thompson polarizers with extinction ratios >10?:1, beam displacers, and UV wave plates, outperforming synthetic crystals like YVO? in the ultraviolet range but requiring AR coatings and humidity control.

Yttrium orthovanadate (YVO?), a positive uniaxial crystal grown by Czochralski method, offers a wide transparency range, large birefringence, and high damage threshold. These properties make it an ideal Calcite/Rutile substitute for optical polarizing components, including fiber isolators, Glan polarizers, and beam displacers. Its mechanical robustness and non-hygroscopicity further enable reliable operation in harsh environments.

High Temperature form BBO (a-BaB2O4) is a negative uniaxial crystal.It has large birefringence over the broad transparent range from 189 nm to 3500 nm.Recently,MT-Optics has succeeded in growing this crystal into large size.The physical,chemical,thermal and optical properties of a-BBO crystal are similar to those of β-BBO.However,the nonlinear optical properties of a-BBO crystal is vanished due to the centric symmetry with its crystal structure,it is not recommended or NLO processes.

Neodymium doped Gadolinium Vanadate (Nd:GdVO4 crystals) belonging to the tetragonal crystal system, is an excellent ideal laser host material for DPSS (Diode Pumped Solid State) micro/mini lasers. It exhibits remarkable physical, optical, and mechanical properties. In terms of laser performance, Nd:GdVO4 crystals demonstrate higher slope efficiency compared to Nd:YAG crystals. When contrasted with Nd:YVO4 crystals, they possess superior thermal conductivity, enabling more stable operation under high-power conditions, and can achieve higher power output. Moreover, its distinct optical anisotropy facilitates efficient polarization control in laser systems. These characteristics make Nd:GdVO4 crystals highly suitable for applications in compact laser devices, such as medical laser equipment, precision laser processing systems, and advanced scientific research laser setups, where high efficiency and stable performance are critical requirements.

Nd:YAG crystal is the most widely used solid-state laser material today. It has been used in the "micro/mini" DPSS (Diode Pumped Solid State) laser system to generate high-quality red, green, or blue laser output. The blue laser from Nd:YAG crystal has higher efficiency and is easier to realize than the blue laser from Nd:YVO4 crystal. Nd:YAG crystal is also widely used in military, scientific, medical, and industrial laser systems, high-performance scientific laser systems, laser therapy, cosmetology systems, laser marking, laser drilling, and other laser material processing systems. Notably, Nd:YAG crystal is the best laser material for high-power, high-energy, and Q-switched pulse laser systems. The extensive applications of Nd:YAG crystal in various laser systems stem from its outstanding physical and mechanical properties.

Nd:YVO4 is one of the most efficient laser host crystals currently existing for diode laser-pumped solid-state lasers. Its large stimulated emission cross-section at lasing wavelength, high absorption coefficient and wide absorption bandwidth at pump wavelength, high laser induced damage threshold as well as good physical, optical and mechanical properties make Nd:YVO4 an excellent crystal for high power, stable and cost-effective diode pumped solid-state lasers.