This article introduces what is frequency quadrupling, the device of frequency quadrupling and the common frequency quadrupling process.

An Effect Using Nonlinear Materials to Achieve Laser Frequency Four Times the Input Light Frequency

Frequency quadrupling is a nonlinear frequency conversion, and the frequency of the obtained light is four times that of the input laser, that is, the wavelength of the output light is one-fourth of the input light. This process can be achieved by using two consecutive frequency multipliers (Figure 1). Another possible approach is to use a frequency doubler and two consecutive sum-frequency generation processes using the remaining pump light, but this approach is not common.

Typical quadrupling setup: An infrared input beam with a wavelength of 1064nm generates a green light with a wavelength of 532nm after a frequency doubling process, and the green light is frequency doubled again to generate light with a wavelength of 266nm.

A common quadrupling process is as follows:

A CW or pulsed light from a Nd:YAG laser with a wavelength of 1064 nm utilizes a frequency doubler (LBO based, Lithium Triborate) to generate green light with a wavelength of 532 nm, which then contributes to a second frequency doubler (CLBO based, Lithium Cesium Borate) produces light with a wavelength of 266nm. Such ultraviolet light has a wide range of applications in many fields, such as: pumping dye lasers or optical parametric oscillators, for Raman spectroscopy, for material processing (eg the preparation of fiber Bragg gratings).

Limited operating life due to crystal degradation As mentioned in the article on frequency triples, nonlinear crystals can degrade due to the action of intense UV light. For the frequency quadrupling process, this short wavelength of UV light also causes the problem of shorter, sometimes more severe, lifetimes of crystals and other optics. For more information, see Frequency Triple.