Home > Nonlinear optics
Nonlinear optics is the branch of optics that describes the behaviour of light in nonlinear media, that is, media in which the polarization P responds nonlinearly to the electric field E of the light. This nonlinearity is typically only observed at very high light intensities such as provided by pulsed lasers.Nonlinear optics gives rise to a host of optical phenomena:
1 Frequency mixing processes
- Second harmonic generation (SHG) or frequency doubling - generation of light with a doubled frequency (half the wavelength)
- Sum-frequency generation (SFG) - generation of light with a frequency that is the sum of two other frequencies (SHG is a special case of this)
- Third harmonic generation (THG) - generation of light with a tripled frequency (one-third the wavelength) (usually done in two steps: SHG followed by SFG of original and frequency-doubled waves)
- Difference-frequency generation (DFG) - generation of light with a frequency that is the difference between two other frequencies
- Parametric amplification - amplification of a signal input in the presence of a higher-frequency pump wave, at the same time generating an idler wave (can be considered as DFG)
- Parametric oscillation - generation of a signal and idler wave using a parametric amplifier in a resonator (with no signal input)
- Parametric generation: like parametric oscillation, but without a resonator - using a very high gain instead
- Optical rectification - generation of quasi-static electric fields.
2 Other nonlinear processes
- Optical Kerr effect (intensity dependent refractive index)
- Self focusing
- Self-phase modulation (SPM)
- Cross-phase modulation (XPM)
- Four-wave mixing (FWM) (can also arise from other nonlinearities)
- Raman scattering (interaction of photons with optical phonons)
- Brillouin scattering (interaction of photons with acoustic phonons)
- Two-photon absorption (simultaneous absorption of two photons, transferring the energy to a single electron)
- Optical phase conjugation (not a separate type of nonlinearity, but an effect arising from nonlinearities such as stimulated Raman or Brillouin scattering)
3 Related processes
In these processes, the medium has a linear response to the light, but the properties of the medium are affected by other causes:
- Pockels effect - the index of refraction is affected by a static electrical field; used in electro-optic modulators
- Acousto-optics - the index of refraction is affected by acoustic waves (ultrasound); used in acousto-optic modulator s
4 Frequency-mixing processes
One of the most commonly-used frequency-mixing processes is frequency doubling or second-harmonic generation. With this technique, the 1064-nm output from or the 800-nm output from can be converted to visible light, with wavelengths of 532 nm (green) or 400 nm (violet), respectively.
Practically, frequency-doubling is carried out by placing a special crystal in a laser beam under a well-chosen angle. Commonly-used crystals are BBO (β- barium borateBoron is the chemical element in the periodic table that has the symbol B and atomic number 5. A trivalent metalloid element, boron occurs abundantly in the ore borax. There are two allotropes of boron; amorphous boron is a brown powder, but metallic boro), KDP ( potassiumpotassium calcium Na K Rb Full table General Name, Symbol, Numberpotassium, K, 19 Series alkali metals Group, Period, Block 1(IA), 4 , s Density, Hardness 856 kg/m3, 0. 4 Appearance silvery white Atomic properties Atomic weight 39. 0983 amu Atomic radius dihydro phosphateIn chemistry, a phosphate is a polyatomic ion or radical consisting of one phosphorus atom and four oxygen. In the ionic form, it carries a -3 formal charge, and is denoted PO3-. In a biochemical setting, a free phosphate ion in solution is called inorgan), and lithiumThis article is about Lithium, the element. For the article on mood-stabilizing drugs, see Lithium salt. Lithium is the chemical element with symbol Li and atomic number 3. In the periodic table, it is located in group 1, among the alkali metals. Lithium niobateNiobium (or columbium is a chemical element in the periodic table that has the symbol Nb and atomic number 41. A rare, soft, gray, ductile transition metal, niobium is found in niobite and used in alloys. The most notable alloys are used to make special s. These crystals have the necessary properties of being strongly birefringentOptics Birefringence or double refraction is the division of a ray of light into two rays (the ordinary ray and the extraordinary ray when it passes through certain types of material, such as calcite crystals, depending on the polarization of the light. (necessary to obtain phase matching, see below), having a specific crystal symmetry and of course being transparent for and resistant against the high-intensity laser light.
