Nonlinear Optics (NLO) Applications : Second harmonic generation (SHG; also ''frequency doubling'' ), optical parametric oscillator (OPO), Electro-Optics ...

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NLO Applications

Nonlinear Optics (NLO) Applications


Second harmonic generation (SHG; also called frequency doubling) is a nonlinear optical process, in which photons interacting with a nonlinear material are effectively "combined" to form new photons with twice the energy, and therefore twice the frequency and half the wavelength of the initial photons.
It is a special case of sum frequency generation.
Today, the most SHG crystals are cut for the conversion of 1.064µm solid-state lasers into green (532nm) but we also manufacture SHG crystals for other visible wavelenghts (red, blue, yellow) or in the UV.
The SHG crystals we manufacture for green (527nm, 532nm) are checked on our SHG test bench.


An optical parametric oscillator (OPO) is a parametric oscillator which oscillates at optical frequencies. It converts an input laser wave (called "pump") into two output waves of lower frequency () by means of second order nonlinear optical interaction. The sum of the output waves frequencies is equal to the input wave frequency:  .
For historic reasons, the two output waves are called "signal" and "idler", where the wave with higher frequency is called signal. A special case is the degenerate OPO, when the output frequency is one-half the pump frequency,  .

The main application of an OPO is to generate longer wavelengths, like pulsed lasers at aroud 1.55 µm, from a 1.064µm pump. The former wavelength lies in the eye-safe band and is commonly used by range-finding devices.

But an OPO can also be used to generate longer wavelengths, or various wavelengths in the visible when pumped at 355nm. Every OPO crystal we manufacture for a pump at 1.064µm and a signal around 1.55µm is checked on our OPO test bench.



The response of electro-optical materials to an electric field is a change of their refractive index. This effect is used in order to change the polarization state of light by applying a voltage to an electro-optical crystal, which acts as a voltage-dependant waveplate.

In practice, this principle is used in Pockels cells where an electro-optical crystal is asociated with a polarizer to block or to transmit light. Pockels cells are used to release pulses ("Q-switch") from a laser resonator or to select pulses from ultrafast lasers (pulse-picker).
Pockels cells made of RTP crystals consist in two birefringence-compensated crystals that can be provided as a pair (unmounted) or as a complete Pockels with electrodes and wires. In each case, the electro-optical response of the component is carefully checked on our test bench.