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 typicall ...

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 particles that can ...

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 and mathematics, wavelength or spatial period of a wave or periodic function is the distance over which the wave's shape repeats. In other words, it is the distance between consecutive corresponding points of the same ''phase (waves ...

). Two types of devices are currently common: ''frequency doublers,'' often based on lithium niobate (LN), lithium tantalate (LT),

potassium titanyl phosphate Potassium titanyl phosphate (KTP) is an inorganic compound with the formula . It is a white solid. KTP is an important nonlinear optics, nonlinear optical material that is commonly used for second-harmonic generation, frequency-doubling diode-pum ...

(KTP) or lithium triborate (LBO), and ''frequency triplers'' typically made of potassium dihydrogen phosphate (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'' originated as an acronym for light amplification by stimulated emission of radi ...

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 known as frequency doubling, is the lowest-order wave-wave nonlinear interaction that occurs in various systems, including optical, radio, atmospheric, and magnetohydrodynamic systems. As a prototype behav ...

(''SHG'', also called frequency doubling), or sum-frequency generation 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 (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 that the

infrared Infrared (IR; sometimes called infrared light) is electromagnetic radiation (EMR) with wavelengths longer than that of visible light but shorter than microwaves. The infrared spectral band begins with the waves that are just longer than those ...

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

electron The electron (, or in nuclear reactions) is a subatomic particle with a negative one elementary charge, elementary electric charge. It is a fundamental particle that comprises the ordinary matter that makes up the universe, along with up qua ...

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 and Novette laser validated the use of frequency tripling KDP crystals to convert the laser light into the

ultraviolet Ultraviolet radiation, also known as simply UV, is electromagnetic radiation of wavelengths of 10–400 nanometers, shorter than that of visible light, but longer than X-rays. UV radiation is present in sunlight and constitutes about 10% of ...

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

References

{{DEFAULTSORT:Optical Frequency Multiplier Second-harmonic generation Frequency multiplier Nonlinear optics Laser science