Laser frequency doubling

Laser frequency doubling refers to a 50% reduction in wavelength and a doubling of frequency through frequency doubling crystals (LBO, BBO).After the crystal doubles the frequency of 1064nm solid light, it comes to 532 green light.

Doubling condition

The condition for frequency doubling is that the crystal can find a direction so that the fundamental frequency laser with frequency f1 and also the frequency doubled light with frequency 2 * f1 can have the very same refractive index (photon energy preservation), to make sure that suitable gain characteristic can exist in the crystal length. The laser can continuously convert the power from the f1 basic frequency to the 2 * f1 frequency doubled light.

The theory of optical frequency doubling

The principle 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 also negative cost facilities. This separation is a dynamic resonance, as well as the resonance frequency follows the frequency of the laser. The resonance amplitude is connected to the strength of the laser area. Because the laser electromagnetic field strength and polarization intensity are nonlinear, for second-order nonlinearity, the polarization intensity is proportional to the square of the laser's electric area strength E.

The strength of the fundamental frequency optical area varies, which can be seen from the trigonometric feature, cosa * cosa= 0.5 *( cos2a +1). The second-order nonlinearity will create double-frequency polarized resonance, as well as zero-frequency, polarized prejudice. This frequency-doubled polarization (resonance of the distance between favorable and unfavorable charges) will produce frequency-doubled light or play a role in getting the passing frequency-doubled laser light.

Frequency-doubled light condition.

This makeover or enhancement of doubled-frequency light requires to meet 2 conditions:

(1) The essential frequency light is ahead of the doubled frequency light by 0.75 π;

(2) The stage difference room stays unchanged in the crystal action area.

The phase distinction room stays the same, calling for the product to have the very same refractive index for both frequencies. Usually, the refractive index of materials enhances with light frequency.

BBO crystals similar to this can satisfy the exact same refractive index in particular instructions. The constant refractive index ensures that the spatial coupling area with a certain length in a specific direction in the crystal is fixed as well as the waveform difference is steady. There is a certain discrepancy in practice, so the coupling length is restricted, which is the particular length of the laser crystal.

Classification of frequency-doubling crystals.

Ammonium dihydrogen phosphate (ADP), potassium dihydrogen phosphate (KDP), potassium dihydrogen phosphate (DKDP), dihydrogen arsenate crucible (DCDA), as well as various other crystals.

They are a representative kind of crystals that create dual-frequency as well as other nonlinear optical impacts, appropriate for use in the near-ultraviolet-visible and near-infrared areas, and also have a big damage threshold.

Lithium niobate (LN), salt barium niobate, potassium niobate, α-type lithium iodate, as well as other crystals.

The second nonlinear electrical polarization coefficient is big, as well as the refractive index of crystals such as LN and BNN is sensitive to temperature, which is various from the temperature level adjustment characteristics of the dispersion effect. Individuals can change the temperature suitably to accomplish non-critical matching. Ideal for the visible light area and also the mid-infrared region (0.4 μ-5μ).

LN is prone to refractive index modification as well as photodamage under light; the damages limit of BNN is more than that of LN, yet the solid remedy area is wider, and also the structure is easy to change, leading to poor optical uniformity, and also big crystals with superb efficiency are challenging to acquire; potassium niobate has no solid solution In the melting zone, it is feasible to get large crystals with uniform optical buildings; α lithium iodate is an aqueous remedy growth crystal, which can grow big crystals with good optical quality, and the damages threshold is greater than that of BNN crystals. The disadvantage is that it has no non-critical matching capacity.

Semiconductor crystals.

Semiconductor crystals consist of gallium arsenide, gallium arsenide, zinc sulfide, cadmium zinc oxide, selenium, etc. Their quadratic nonlinear electrical polarization coefficients are more than those of the very first two crystals as well as appropriate for bigger infrared bands.

Nonetheless, besides selenium as well as tellurium, a lot of crystals have no double refraction result and can not attain position matching.

Borate, barium metaborate (BBO crystal), lithium tri borate (LiB3O5), etc.

Among them, Researchers efficiently developed barium metaborate and lithium tri borate crystals for the very first time in the 1980s. As well as had the impressive benefits of large nonlinear optical coefficients and high laser damages limit. It is an outstanding crystal material for laser frequency conversion, which has actually created excellent consequences worldwide. Appropriate for ultraviolet wavelengths, consisting of KBF, and so on, and also for deep ultraviolet wavelengths. The standard needs for the sum frequency, distinction frequency, and also optical criterion oscillation impacts of nonlinear optical crystals coincide with those of dual-frequency crystals.