The Laser Induced Damage Threshold (LIDT) defines the maximum amount of laser radiation that an optical device can handle without causing damage. It is one of the most important specifications to consider when integrating optics into a laser.
Ultraviolet Lasers
The use of UV lasers offers many advantages over longer wavelengths such as infrared or visible light. In materials processing, infrared or visible light lasers melt or vaporize material, which can prevent the creation of small, precise features and compromise the structural integrity of the substrate. UV lasers, on the other hand, process materials by directly breaking atomic bonds in the substrate, which means that no peripheral heating occurs around the beam spot. This reduces damage to the material and allows UV lasers to process thin, delicate materials more efficiently than visible and infrared lasers. The lack of peripheral heating also helps to create very precise incisions, holes and other fine features. In addition, laser spot size is proportional to wavelength. As a result, UV lasers have higher spatial resolution than visible or infrared lasers and lead to more precise processing of materials.
However, the short wavelength of UV lasers affects the LIDT of the optics with which they are used.UV light scatters more than visible or infrared light and also contains more energy, causing it to be absorbed by the substrate. Similar to how UV lasers cut through materials by breaking atomic bonds, the unwanted absorption of UV lasers breaks bonds in optical components or coatings, leading to failure. This reduces the LIDT of the component, and optics typically have a lower LIDT at UV wavelengths than at visible or infrared wavelengths. When dealing with LIDT, it is important to remember that LIDT is directly related to wavelength.
UV Optical Devices
UV optics devices must be carefully designed and fabricated to withstand the effects of UV damage. UV optics must contain fewer bubbles than usual, have a uniform refractive index throughout the optics, and have a limited birefringence, a specification that correlates the polarization of light with the refractive index of the optics. Additionally, in cases involving the use of UV lasers, UV optics should be considered for prolonged exposure. An example of a material used in UV applications is calcium fluoride (CaF2), which has all of the above properties required to withstand UV damage. However, in some applications, even CaF2 optics can be damaged. For example, if you use CaF2 optics in high humidity environments, they will perform poorly because they are highly hygroscopic and easily absorb moisture.
Therefore, when using a UV laser, it is critical to consider the laser damage threshold. LIDT specifications can be misleading if the optics chosen are not made for UV wavelengths. For standard laser optics, LIDT will rarely be performed for wavelengths in the UV portion of the spectrum. instead, LIDT will be used for higher wavelengths. UV Optics offers a LIDT that is specifically tested using UV wavelengths, ensuring a more accurate LIDT specification.
