Optical Crystals Information

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Optical crystals are transparent in different spectral regions, depending upon the crystal material. They include nonlinear, photorefractive crystals, and laser crystals’ acousto-optic and electro-optic combinations; X-ray analysis and scintillation crystals; and other types of crystals that are used in semiconductors.

Optical crystals

Operation

Optical crystals are used mainly in laser applications. For example, non-linear devices are used as frequency converters and consist of a crystal made of lithium niobate, barium borate, lithium triborate, and potassium titanyl phosphate. Each has specific operating characteristics and should be selected based on the laser application. For example, a lithium niobate crystal may be used as a frequency doubler in an optical parametric oscillator (OPO) device.

Optical crystals can be used in many different infrared (IR) laser applications. Examples include scintillation detectors and gas analyzers. These crystals are also widely used in military infrared optical devices. Crystal sapphire optical components are used in high power laser windows. Some optical crystals are clear or colorless. Acousto-optical crystals such as tellurium dioxide can be used in argon laser applications.

Types of Optical Crystals

There are multiple types of optical crystals

Acousto-Optic: Acousto-optic crystals have changes in refractive index of the medium due to sound waves that are present in the medium.
Birefringent: Birefringent crystals refractive index depends on the polarization direction of transmitted light. Birefringent crystals are commonly used to make waveplates or retarders, polarizers and prisms.
Electro-Optic: Electro-optic crystals are crystals that exhibit Pockels Effect (linear effect) or Kerr Effect (non-linear effect). A refractive index that changes proportionally to the electric field is the Pockels Effect. A refractive index that changes proportionally to the square of the electric field is the Kerr Effect.
Laser: Laser crystals generate laser light when an energized by an energy source.
Nonlinear: Nonlinear (NLO) crystals generate nonlinear optical effects from lasers, electricity, magnetic fields, or strain field.
Photorefractive: Photorefractive crystals have changes to the refractive index, which are modified by spatial variations of light intensity.
Q-Switch: Q-switch crystals when excited by laser light, store energy when in a saturated state. Its transmission increases, reducing the resonator loss, and laser pulse is generated.
Scintillation: A scintillation crystal absorbs X-ray, gamma-rays, alpha ray, and beta ray and converts some of their energy into visible light and ultraviolet (UV) photons.

Configurations

Optical crystals are commonly made of the following materials:

BBO: Beta-barium borate (beta-BaB204) has high levels of transparency and wide phase matching ranges. It has a large nonlinear coefficient, high damage threshold, and good optical homogeneity.
BIBO: Bismuth borate (BiB3O6) is a nonlinear optical crystal with wide transparency range, large nonlinear coefficient, and high damage threshold.
KDP and KD*P: Potassium dihydrogen phosphate (KH2PO4) and potassium dideuterium phosphate (KD2PO4) optical crystals are one of the most commonly used nonlinear materials.
KTP: KTP are high purity, low absorption optical crystals. KTP also have large nonlinear optical coefficients, wide angular bandwidth, and low dielectric constant.
KTA: KTA (KTiOAsO4) or potassium titanyl arsenate has large optical and electro-optical coefficients with wide angular bandwidth and spectral bandwidth. KTA also has a high resistance to laser radiation.
Infrared Nonlinear ZnGeP2 (ZGP): ZnGeP2 (zinc germanium phosphide) optical crystals are nonlinear near infrared tunable crystals. They have relatively high laser damage threshold and good optical transparency.
LBO: Lithium tri-borate (LiB3O5) has a large conversion coefficient and wide optical transparency.
LiNbO3 : LiNbO3 optical crystals are used commonly as frequency doublers due to their large electro-optic and acousto-optic coefficients.
RTP: RTP (RbTiOPO4) crystals are nonlinear optical crystals with high damage threshold, large optical coefficient, and have excellent performance.
TGG: Terbium gallium garnet (Tb3Ga5O12) optical crystals are used in the visible to near-infrared wavelengths and have high thermal conductivity and low optical loss.
YCOB: Yttrium calcium oxyborate (YCa4O(BO3)3) optical crystals are nonlinear crystals with high damage intensity and can be used in the UV frequency range.

Specifications and Features

Specifications

The following specifications determine the functionality of an optical crystal.

Dimensions: the physical dimensions of the crystal.
Crystal orientation: the propagation direction is broken into the azimuthal angle (Phi) and the polar angle (Theta). The azimuthal angle is the angle between the projection of propagation direction onto the XY plane and the x-axis. The polar angle is the angle between the optical axis and the propagation direction.
Optical specifications: damage threshold, refractive index and transparency range. The damage threshold, or LASER inducted damage threshold, is the amount of damage the crystal can withstand from laser pulses. Refractive Index is defined as n = c/v, where n is the refractive index, c is the speed of light in a vacuum and v is the velocity of light in the media. The transparency range is the optical crystals wavelength range that light can pass through the material without much scattering.

Features

These features provide additional utility or ease-of-use.

AR-coated: The optical crystal has an AR (anti-reflective) coating.
Laser/heat resistant: Optical crystals are rated for use with lasers or are heat resistant.