Laser frequency doubling describes the laser whose wavelength is minimized by fifty percent, and the frequency is doubled with the frequency doubling crystal (LBO, BBO). After the crystal doubles the frequency of 1064nm powerful light, it ends up being 532 green light.
The problem for frequency doubling is that the crystal can locate an instructions to make sure that the essential frequency laser with frequency f1 and also the frequency doubled light with frequency 2 * f1 can have the same refractive index (photon energy conservation), to ensure that perfect gain feature can exist in the crystal size. The laser can continually convert the power from the f1 fundamental frequency to the 2 * f1 frequency doubled light.
The principle of optical frequency doubling
The concept basis for the frequency doubling of light is the nonlinear result of laser light. The laser light is so intense that it triggers the atomic polarization of the crystalline product, that is, the splitting up of favorable and adverse charge facilities. This splitting up is a dynamic vibration, as well as the vibration frequency follows the frequency of the laser. Due to the fact that the laser magnetic field strength and also polarization intensity are nonlinear, for second-order nonlinearity, the polarization intensity is symmetrical to the square of the laser’s electric area strength E.
The strength of the essential frequency optical area varies, which can be seen from the trigonometric feature, cosa * cosa= 0.5 *( cos2a +1). The second-order nonlinearity will certainly create double-frequency polarized vibration as well as zero-frequency polarized prejudice. This frequency-doubled polarization (resonance of the distance in between positive and adverse charges) will produce frequency-doubled light or play a role in getting the passing frequency-doubled laser light.
Frequency-doubled light problem
This transformation or enhancement of doubled-frequency light needs to meet two problems:
- The fundamental frequency light leads the doubled frequency light by 0.75 π;
- The phase difference space stays unchanged in the crystal action region.
The stage difference room stays the very same, calling for the product to have the same refractive index for both frequencies. Typically, the refractive index of materials raises with light frequency.
BBO crystals like this can satisfy the exact same refractive index in a certain direction. The constant refractive index makes certain that the spatial combining area with a specific size in a specific direction in the crystal is repaired as well as the waveform distinction is steady. There is a certain deviation in practice, so the coupling size is restricted, which is the particular length of the laser crystal.
Classification of frequency-doubling crystals
They are a depictive style of crystals that produce dual-frequency and also various other nonlinear optical impacts, are suitable for use in the near-ultraviolet-visible and near-infrared areas, as well as have a big damage threshold.
The additional nonlinear electrical polarization coefficient is huge, and also the refractive index of crystals such as LN and also BNN is sensitive to temperature level, which is various from the temperature level change attributes of the dispersion effect. People can adjust the temperature level appropriately to accomplish non-critical matching. Suitable for the noticeable light region and also mid-infrared region (0.4 μ-5μ). LN is prone to refractive index adjustment and also photodamage under light; the damages threshold of BNN is higher than that of LN, yet the solid option region is broader, as well as the make-up is simple to alter, resulting in poor optical harmony, and huge crystals with exceptional performance are hard to acquire; potassium niobate has no solid remedy In the melting zone, it is possible to get huge crystals with consistent optical homes; α lithium iodate is an aqueous service growth crystal, which can grow large crystals. The negative aspect is that it has no non-critical matching ability.
Semiconductor crystals include gallium arsenide, gallium arsenide, zinc sulfide, cadmium zinc oxide, selenium, and so on. Their quadratic nonlinear electrical polarization coefficients are greater than those of the initial two crystals and are suitable for broader infrared bands.
However, except for selenium as well as tellurium, the majority of crystals have no double refraction effect as well as can not attain setting matching.
Borate, barium metaborate (β-BaB2O4), lithium triborate (LiB3O5), etc.
Among them, Researchers effectively created barium metaborate and also lithium triborate crystals for the first time in the 1980s. As well as had the impressive benefits of big nonlinear optical coefficients and high laser damages limit. Ideal for ultraviolet wavelengths, including KBF, etc, even for deep ultraviolet wavelengths. The fundamental demands for the amount frequency, difference frequency, as well as optical parameter oscillation results of nonlinear optical crystals coincide as those of dual-frequency crystals.