Optics for Er:YAG lasers

Overview

The part of the Mid-IR spectral region, spanning wavelengths from 2μm to 5μm, holds quite a significance in various applications. When it comes to Mid-IR lasers, the most prominent applications are laser processing, defence and medical applications, environmental monitoring, however, the potential of this spectral region reaches far, penetrating many areas of applications. The successful operations of mid-IR lasers rely heavily on the performance of optical components. That’s why here at OPTOMAN we like to say “With great [laser] power comes great responsibility [for coaters]”.

Laser optics for this region must feature high spectral performance and low absorption. Although scattering might not be a significant issue when speaking of Mid-IR optics due to the long wavelengths, absorption remains a serious concern, because it leads to reduced Laser-Induced Damage Threshold (LIDT).

And here‘s where OPTOMAN comes in. OPTOMAN concentrates solely on the most advanced sputtering technology - Ion-Beam Sputtering (IBS), which offers many great capabilities in depositing thin film coatings with great uniformity and bulk-like density.

Why is IBS more advantageous?

IBS solves key problems for Mid-IR coatings by:

Improving coating density

Ensuring long-term durability in harsh and dynamic environments.

Minimizing absorption losses

Which helps optimize the output power of lasers.

Improving LIDT

Enabling operation at high-power levels.

So what are the challenges related to using IBS for Mid-IR coatings?

Film Stress. It is true that IBS coatings due to high density have higher stress values that can lead to coating cracking or peeling. At OPTOMAN, by introducing specific pre- and post- coating processes, we were able to reduce the stress which leads to fewer of the aforementioned problems.
Adhesion issues. Substrate material properties as well as differences in thermal expansion coefficients typically cause adhesion issues for IBS coatings. OPTOMAN was no exception, but R&D department found the way to make high repeatability optics for Mid-IR.
High cost. Coatings for Mid-IR spectral region are usually quite thick, which sometimes motivates to avoid IBS coatings and sacrifice some of the performance for the better price provided by alternative coating technologies or metal coatings. However, OPTOMAN now offers two alternatives that addresses the cost drivers:
1) Scale. OPTOMAN has one of the largest IBS coating chambers in the World enabling to reduce the cost per piece significantly.
2) Coating thickness. Recent R&D achievement enables OPTOMAN to offer relatively thin coatings that perform like you would expect from IBS coatings but with a significantly reduced price. This technology is suitable for <100 GW/cm2 laser power levels and is a perfect choice for laser communication applications, environmental monitoring, sensing and imaging. By this innovation, you can remain at your target price, but improve your laser system performance by advanced IBS coatings.

Due to these challenges, it is not common to manufacture Mid-IR laser optics with IBS technology. However, OPTOMAN has overcome and solved these problems and confidently believes that using IBS is advantageous for the reasons mentioned above. OPTOMAN can make all types of coatings – anti-reflective, mirrors, GTI mirrors, polarizers, partial reflectors, dichroic mirrors, etc. up to 5000nm.

Optics for Er:YAG lasers

One of the most common lasers in this spectral region is the Er:YAG laser. It emits light that strongly corresponds to absorption bands in water, thus it is well suitable for medical applications. OPTOMAN is capable of manufacturing long lifetime and high LIDT laser optics at 2940 nm with high confidence because of the procedures which lead to almost full reduction of OH group absorption inside the coating.