Optical rectification
Encyclopedia
Electro-optic rectification (EOR) (also referred to as optical rectification) is a non-linear optical process which consists in the generation of a quasi-DC polarization in a non-linear medium at the passage of an intense optical beam. For typical intensities, optical rectification is a second-order phenomenon (difference frequency mixing) which is based on the inverse process of the electro-optic effect
. It was reported for the first time in 1962, when radiation from a ruby laser
was transmitted through potassium dihydrogen phosphate (KDP) and potassium dideuterium phosphate (KDdP) crystals.
, where an AC signal is converted ("rectified") to DC.
When the applied electric field is delivered by a femtosecond-pulse-width laser
, the spectral bandwidth associated with such short pulses is very large. The mixing of different frequency components produces a beating polarization, which results in the emission of electromagnetic waves in the terahertz region. The EOR effect is somewhat similar to a classical electrodynamic emission of radiation by an accelerating/decelerating charge, except that here the charges are in a bound dipole form and the THz generation depends on the second order susceptibility of the nonlinear optical medium. A popular material for generating radiation in the 0.5–3 THz range (1 mm wavelength) is zinc telluride
.
Optical rectification also occurs on metal
surfaces by similar effect as surface second harmonic generation
. The effect is however influenced e. g. by nonequilibrium electron excitation and generally it manifests in a more complicated way.
where a polar lattice vibration is thought to generate the terahertz radiation
.
in the departments of Electrical Engineering and Computer Science, Physics and Applied Physics, claims to have found a way to make an "optical battery"
. This new technique could make solar power cheaper, the researchers say.
Electro-optic effect
An electro-optic effect is a change in the optical properties of a material in response to an electric field that varies slowly compared with the frequency of light...
. It was reported for the first time in 1962, when radiation from a ruby laser
Ruby laser
A ruby laser is a solid-state laser that uses a synthetic ruby crystal as its gain medium. The first working laser was a ruby laser made by Theodore H. "Ted" Maiman at Hughes Research Laboratories on May 16, 1960....
was transmitted through potassium dihydrogen phosphate (KDP) and potassium dideuterium phosphate (KDdP) crystals.
Explanation
Optical rectification can be intuitively explained in terms of the symmetry properties of the non-linear medium: in the presence of a preferred internal direction, the polarization will not reverse its sign at the same time as the driving field. If the latter is represented by a sinusoidal wave, then an average DC polarization will be generated. This is the analogue of the electric rectification effectRectifier
A rectifier is an electrical device that converts alternating current , which periodically reverses direction, to direct current , which flows in only one direction. The process is known as rectification...
, where an AC signal is converted ("rectified") to DC.
When the applied electric field is delivered by a femtosecond-pulse-width laser
Laser
A laser is a device that emits light through a process of optical amplification based on the stimulated emission of photons. The term "laser" originated as an acronym for Light Amplification by Stimulated Emission of Radiation...
, the spectral bandwidth associated with such short pulses is very large. The mixing of different frequency components produces a beating polarization, which results in the emission of electromagnetic waves in the terahertz region. The EOR effect is somewhat similar to a classical electrodynamic emission of radiation by an accelerating/decelerating charge, except that here the charges are in a bound dipole form and the THz generation depends on the second order susceptibility of the nonlinear optical medium. A popular material for generating radiation in the 0.5–3 THz range (1 mm wavelength) is zinc telluride
Zinc telluride
Zinc telluride is a binary chemical compound with the formula ZnTe. This solid is a semiconductor material with band gap of 2.23–2.25 eV. It is usually a P-type semiconductor. Its crystal structure is cubic, like that for sphalerite and diamond....
.
Optical rectification also occurs on metal
Metal
A metal , is an element, compound, or alloy that is a good conductor of both electricity and heat. Metals are usually malleable and shiny, that is they reflect most of incident light...
surfaces by similar effect as surface second harmonic generation
Surface second harmonic generation
Surface second harmonic generation is a method for probing interfaces in atomic and molecular systems. In second harmonic generation , the light frequency is doubled, essentially converting two photons of the original beam of energy E into a single photon of energy 2E as it interacts with...
. The effect is however influenced e. g. by nonequilibrium electron excitation and generally it manifests in a more complicated way.
Applications
Together with carrier acceleration in semiconductors and polymers, optical rectification is one of the main mechanisms for the generation of terahertz radiation using lasers. This is different from other processes of terahertz generation such as polaritonicsPolaritonics
Polaritonics is an intermediate regime between photonics and sub-microwave electronics . In this regime, signals are carried by an admixture of electromagnetic and lattice vibrational waves known as phonon-polaritons, rather than currents or photons...
where a polar lattice vibration is thought to generate the terahertz radiation
Terahertz radiation
In physics, terahertz radiation refers to electromagnetic waves propagating at frequencies in the terahertz range. It is synonymously termed submillimeter radiation, terahertz waves, terahertz light, T-rays, T-waves, T-light, T-lux, THz...
.
Energy Conversion
Stephen Rand, a professor at University of MichiganUniversity of Michigan
The University of Michigan is a public research university located in Ann Arbor, Michigan in the United States. It is the state's oldest university and the flagship campus of the University of Michigan...
in the departments of Electrical Engineering and Computer Science, Physics and Applied Physics, claims to have found a way to make an "optical battery"
. This new technique could make solar power cheaper, the researchers say.