Laser Frequency Doubling

Laser frequency doubling describes the laser whose wavelength is lowered by fifty percent, and also the frequency is doubled by the frequency doubling crystal (LBO, BBO). After the crystal doubles the frequency of 1064nm solid light, it becomes 532 green light.

Doubling condition

The problem for frequency doubling is that the crystal can discover a direction to make sure that the fundamental frequency laser with frequency f1 and the frequency doubled light with frequency 2 * f1 can have the same refractive index (photon momentum conservation), to make sure that optimal gain feature can exist in the crystal size. The laser can continually convert the power from the f1 basic frequency to the 2 * f1 frequency doubled light.

The principle 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 extreme that it triggers the atomic polarization of the crystalline material, that is, the separation of favorable and unfavorable charge facilities. This separation is a dynamic resonance, as well as the vibration frequency, is consistent with the frequency of the laser. The vibration amplitude is related to the intensity of the laser area. Due to the fact that the laser magnetic field strength and also polarization strength is nonlinear, for second-order nonlinearity, the polarization intensity is proportional to the square of the laser's electric area intensity E.

The intensity of the fundamental frequency optical area changes, which can be seen from the trigonometric function, cosa * cosa= 0.5 *( cos2a +1). The second-order nonlinearity will produce double-frequency polarized vibration as well as zero-frequency polarized prejudice. This frequency-doubled polarization (resonance of the range between favorable and also adverse costs) will certainly create frequency-doubled light or contribute in gaining the passing frequency-doubled laser light.

Frequency-doubled light problem.

This makeover or enhancement of doubled-frequency light requires to fulfill two problems:

(1) The basic frequency light leads the doubled frequency light by 0.75 π;

(2) The phase difference area stays unmodified in the crystal activity area.

The phase distinction area remains the very same, needing the product to have the very same refractive index for both frequencies. Usually, the refractive index of products boosts with light frequency.

BBO crystals such as this can meet the exact same refractive index in certain instructions. The regular refractive index guarantees that the spatial coupling area with a specific size in certain instructions in the crystal is fixed and the waveform difference is steady. There is a specific deviation in practice, so the combining size is limited, which is the particular size 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), and also various other crystals.

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

Lithium niobate (LN), salt barium niobate, potassium niobate, α-type lithium iodate, and also various other crystals.

The additional nonlinear electric polarization coefficient is huge, and the refractive index of crystals such as LN as well as BNN is sensitive to temperature, which varie from the temperature level adjustment features of the diffusion impact. People can readjust the temperature level suitably to accomplish non-critical matching. Appropriate for the noticeable light area as well as the mid-infrared area (0.4 μ-5μ). LN is prone to refractive index change and photodamage under light; the damage limit of BNN is more than that of LN, but the strong remedy area is larger, as well as the structure is easy to transform, causing inadequate optical uniformity, and also big crystals with excellent efficiency are tough to get; potassium niobate has no strong service In the melting zone, it is feasible to obtain big crystals with consistent optical residential or commercial properties; α lithium iodate is a liquid service growth crystal, which can expand big crystals with excellent optical quality, as well as the damages threshold is more than that of BNN crystals. The downside 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 square nonlinear electric polarization coefficients are more than those of the first 2 crystals and also appropriate for bigger infrared bands

Nevertheless, except for selenium and tellurium, the majority of crystals have no dual refraction result and can not attain setting matching.

Borate, barium metaborate (β-BaB2O4), lithium triborate (LiB3O5), and so on.

Amongst them, Researchers efficiently created barium metaborate and also lithium triborate crystals for the first time in the 1980s. As well as had the superior benefits of big nonlinear optical coefficients as well as high laser damages limit. It is an exceptional crystal material for laser frequency conversion, which has actually created terrific consequences worldwide. Ideal for ultraviolet wavelengths, consisting of KBF, etc, even for deep ultraviolet wavelengths. The basic requirements for the amount frequency, distinction frequency, and also optical parameter oscillation effects of nonlinear optical crystals are the same as those of dual-frequency crystals.

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