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Frequency Quadrupling

Author: the photonics expert Dr. Rüdiger Paschotta (RP)

Definition: the phenomenon that an input laser beam generates a beam with four times the optical frequency

Alternative term: fourth-harmonic generation

More general term: nonlinear frequency conversion

Category: article belongs to category nonlinear optics nonlinear optics

DOI: 10.61835/ucg Cite the article: BibTex plain text HTML Link to this page! LinkedIn

Frequency quadrupling is a process of nonlinear frequency conversion where the resulting optical frequency is four times that of the input laser beam, which means that the wavelength is reduced by a factor of 4. That can be accomplished with two sequential frequency doublers (Figure 1). Another possibility would be to use a single frequency doubler and two sum frequency generation stages for mixing with residual pump light, but that approach is not common.

A common type of frequency quadrupling configuration begins with a continuous-wave or pulsed Nd:YAG laser at 1064 nm for generating 532-nm light in a first frequency doubler stage (based e.g. on LBO = lithium triborate) and then 266 nm in a second stage (based e.g. on CLBO = cesium lithium borate). Such ultraviolet light is useful e.g. for pumping a dye laser or an optical parametric oscillator, for Raman spectroscopy in flames, or for laser material processing, e.g. the writing of fiber Bragg gratings.

Limited Lifetime due to Crystal Degradation

As explained in the article on frequency tripling, nonlinear crystals can be degraded during operation by the intense ultraviolet light. For frequency quadrupling, the correspondingly shorter UV wavelength tentatively cause stronger problems of that type, compared with frequency tripling, and lead to short lifetimes of crystals and other optics. Otherwise, similar aspects apply as discussed in the article on frequency tripling.

More to Learn

Frequency doubling

Frequency tripling

Nonlinear frequency conversion

Ultraviolet lasers

Suppliers

The RP Photonics Buyer's Guide contains 16 suppliers for frequency quadrupling devices. Among them:

HC Photonics

HC Photonics (HCP) offers both commercial off-the-shelf (COTS) and custom PPMgO:LN or PPMgO:LT based frequency quadrupling devices for pump wavelength ranging from 1420 nm to 5000 nm.

The product mix includes bare crystals and plug-and-play fibered mixers with either one cascaded design or two-stage conversion configurations.

A typical reference spec is the 488 nm fibered mixer converted from 1952 nm fiber laser.

Please contact us for solutions to meet your specific demands.

EKSMA OPTICS

EKSMA Optics offers a wide variety of nonlinear materials which are well suited for quadrupling applications starting with different laser wavelengths. The most popular choices are BBO and KDP crystals. We also have the even more efficient custom CLBO crystals.

APE

The HarmoniXX FHG – Fourth Harmonic Generation – is a frequency converter for quadrupling the frequency of ultrashort pulse lasers.

The focus is on user-friendliness and a compact design. By featuring a quick exchange of optics, the HarmoniXX devices can be used for a wide pulse duration range, from femtoseconds (fs) to several picoseconds (ps). All units are optimized for highest conversion efficiency at various laser power levels. They also display minimum pulse broadening while maintaining good spatial beam profile.

For more details, see our specifications.

Shalom EO

Shalom EO offers a vast selection of nonlinear optical crystals for frequency quadrupling, also known as fourth harmonic generation (FHG). Shalom EO supplies different kinds of NLO crystals including BBO crystals, CLBO crystals, KDP and KD^*P, KTA, PPLN waveguides, LBO, KTP, HGTR KTP, BIBO, LiNbO₃ and MgO:LiNbO₃ crystals, YCOB, in addition to the infrared nonlinear crystals ZnGeP₂ (ZGP) and LiIO₃. Miscellaneous coating options including uncoated, AR, HR, HT, PR coatings, electrodes, and custom coatings are available.

Both off-the-shelf and customized products are available. The crystals can be offered in the form of ingots, blanks, and laser-grade polished elements.

Recent days, Shalom EO launched CLBO (cesium lithium borate) crystals. Processed and polished in low humidity workshop, our CLBO crystals feature excellent performance in UV, vacuum UV (VUV), and deep UV (DUV) wavelength ranges.

Ultra-thin nonlinear crystals for femto-line lasers are also available.

TOPTICA Photonics

TOPTICA provides frequency-quadrupled continuous-wave diode and fiber lasers based on two cascaded frequency-doubling stages. Available wavelengths range from 190 nm to 390 nm with up to 10 nm of tuning. Furthermore, the novel Super-UV technology guarantees long-term stable operation and higher powers at DUV wavelengths.

Bibliography

[1]	J. Reintjes and R. C. Eckardt, “Efficient harmonic generation from 532 to 266 nm in ADP and KD^*P”, Appl. Phys. Lett. 30, 91 (1977); https://doi.org/10.1063/1.89300
[2]	D. Bruneau et al., “Fourth harmonic generation of a large-aperture Nd:glass laser”, Appl. Opt. 24 (22), 3740 (1985); https://doi.org/10.1364/AO.24.003740
[3]	B. A. Hooper et al., “Fourth-harmonic generation in a single lithium niobate-crystal with cascaded second-harmonic generation”, Appl. Opt. 33 (30), 6980 (1994); https://doi.org/10.1364/AO.33.006980
[4]	M. Oka et al., “All solid-state continuous-wave frequency-quadrupled Nd:YAG laser”, J. Sel. Top. Quantum Electron. 1 (3), 859 (1995); https://doi.org/10.1109/2944.473671
[5]	J. Knittel and A. H. Kung, “Fourth harmonic generation in a resonant ring cavity”, IEEE J. Quantum Electron. 33 (11), 2021 (1997); https://doi.org/10.1109/3.641318
[6]	T. Kojima et al., “20-W ultraviolet-beam generation by fourth-harmonic generation of an all-solid-state laser”, Opt. Lett. 25 (1), 58 (2000); https://doi.org/10.1364/OL.25.000058
[7]	T. Südmeyer et al., “Efficient 2^nd and 4^th harmonic generation of a single-frequency, continuous-wave fiber amplifier”, Opt. Express 16 (3), 1546 (2008); https://doi.org/10.1364/OE.16.001546

(Suggest additional literature!)

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