An optical frequency multiplier is a

nonlinear optical Nonlinear optics (NLO) is the branch of optics that describes the behaviour of light in ''nonlinear media'', that is, media in which the polarization density P responds non-linearly to the electric field E of the light. The non-linearity is typic ...

device in which

photon A photon () is an elementary particle that is a quantum of the electromagnetic field, including electromagnetic radiation such as light and radio waves, and the force carrier for the electromagnetic force. Photons are massless, so they always ...

s interacting with a nonlinear material are effectively "combined" to form new photons with greater energy, and thus higher frequency (and shorter

wavelength In physics, the wavelength is the spatial period of a periodic wave—the distance over which the wave's shape repeats. It is the distance between consecutive corresponding points of the same phase on the wave, such as two adjacent crests, tro ...

). Two types of devices are currently common: ''frequency doublers,'' often based on

lithium niobate Lithium niobate () is a non-naturally-occurring salt consisting of niobium, lithium, and oxygen. Its single crystals are an important material for optical waveguides, mobile phones, piezoelectric sensors, optical modulators and various other linea ...

(LN),

lithium tantalate Lithium tantalate ( Li Ta O3) is a perovskite which possesses unique optical, piezoelectric and pyroelectric properties which make it valuable for nonlinear optics, passive infrared sensors such as motion detectors, terahertz generation and de ...

(LT),

potassium titanyl phosphate Potassium is the chemical element with the symbol K (from Neo-Latin ''kalium'') and atomic number19. Potassium is a silvery-white metal that is soft enough to be cut with a knife with little force. Potassium metal reacts rapidly with atmospher ...

(KTP) or

lithium triborate Lithium triborate (LiB3O5) or LBO is a non-linear optics crystal. It has a wide transparency range, moderately high nonlinear coupling, high damage threshold and desirable chemical and mechanical properties. This crystal is often used for seco ...

(LBO), and ''frequency triplers'' typically made of

potassium dihydrogen phosphate Monopotassium phosphate (MKP) (also, potassium dihydrogenphosphate, KDP, or monobasic potassium phosphate) is the inorganic compound with the formula KH2PO4. Together with dipotassium phosphate (K2HPO4.(H2O)x) it is often used as a fertilizer, ...

(KDP). Both are widely used in optical experiments that use

laser A laser is a device that emits light through a process of optical amplification based on the stimulated emission of electromagnetic radiation. The word "laser" is an acronym for "light amplification by stimulated emission of radiation". The fir ...

s as a light source.

Harmonic generation

There are two processes that are commonly used to achieve the conversion:

second-harmonic generation Second-harmonic generation (SHG, also called frequency doubling) is a nonlinear optical process in which two photons with the same frequency interact with a nonlinear material, are "combined", and generate a new photon with twice the energy of ...

(''SHG'', also called frequency doubling), or

sum-frequency generation Sum-frequency generation (SFG) is a second order nonlinear optical process based on the annihilation of two input photons at angular frequencies \omega_1 and \omega_2 while, simultaneously, one photon at frequency \omega_3 is generated. As with a ...

which sums two non-similar frequencies. Direct third-harmonic generation (''THG'', also called frequency tripling) also exists and can be used to detect an interface between materials of different excitability. For example, it has been used to extract the outline of cells in embryos, where the cells are separated by water.Nonlinear microscopy and tissue morphogenesis
Laboratoire d'Optique et Biosciences, École Polytechnique, France

Lasers

Optical frequency multipliers are common in high-power lasers, notably those used for

inertial confinement fusion Inertial confinement fusion (ICF) is a fusion energy process that initiates nuclear fusion reactions by compressing and heating targets filled with thermonuclear fuel. In modern machines, the targets are small spherical pellets about the size of ...

(ICF) experiments. ICF attempts to use a laser to heat and compress a target containing fusion fuel, and it was found in experiments with the

Shiva laser The Shiva laser was a powerful 20-beam infrared neodymium glass (silica glass) laser built at Lawrence Livermore National Laboratory in 1977 for the study of inertial confinement fusion (ICF) and long-scale-length laser-plasma interactions. Presu ...

that the

infrared Infrared (IR), sometimes called infrared light, is electromagnetic radiation (EMR) with wavelengths longer than those of visible light. It is therefore invisible to the human eye. IR is generally understood to encompass wavelengths from around ...

frequencies generated by the laser lost most of its energy in the hot

electron The electron ( or ) is a subatomic particle with a negative one elementary electric charge. Electrons belong to the first generation of the lepton particle family, and are generally thought to be elementary particles because they have no kn ...

s being generated early in the heating process. In order to avoid this problem much shorter wavelengths needed to be used, and experiments on the

OMEGA laser The Laboratory for Laser Energetics (LLE) is a scientific research facility which is part of the University of Rochester's south campus, located in Brighton, New York. The lab was established in 1970 and its operations since then have been fund ...

and

Novette laser Novette was a two beam neodymium glass (phosphate glass) testbed laser built at Lawrence Livermore National Laboratory in about 15 months throughout 1981 and 1982 and was completed in January 1983. Novette was made using recycled parts from the dis ...

validated the use of frequency tripling

KDP KDP may refer to: * Communist Party of Germany (Kommunistische Partei Deutschlands) * Kurdistan Democratic Party of Iraqi Kurdistan * Kurdish Democratic Party of Iran of Iranian Kurdistan * Korea Democratic Party * Khmer Democratic Party *Kappa Del ...

crystals to convert the laser light into the

ultraviolet Ultraviolet (UV) is a form of electromagnetic radiation with wavelength from 10 nanometer, nm (with a corresponding frequency around 30 Hertz, PHz) to 400 nm (750 Hertz, THz), shorter than that of visible light, but longer than ...

, a process that has been used on almost every laser-driven ICF experiment since then, including the

National Ignition Facility The National Ignition Facility (NIF) is a laser-based inertial confinement fusion (ICF) research device, located at Lawrence Livermore National Laboratory in Livermore, California, United States. NIF's mission is to achieve fusion ignition wit ...

References

{{DEFAULTSORT:Optical Frequency Multiplier Second-harmonic generation

Frequency multiplier In electronics, a frequency multiplier is an electronic circuit that generates an output signal and that output frequency is a harmonic (multiple) of its input frequency. Frequency multipliers consist of a nonlinear circuit that distorts the in ...

Nonlinear optics Laser science