Diamond has some salient features: for example, its refractive index is 2.4, which is very high and can achieve thinner optical elements through the same optical power. Their thermal conductivity is over 2000W/(m·K), 1400 times higher than the optical glass. In addition to the high damage threshold, these features make diamond very meaningful for high power optical systems.

To date, polycrystalline diamond substrates are used only as windows for carbon dioxide lasers. Due to the presence of impurities and defects, they absorb and scatter laser radiation at an emission wavelength of about 1μm, unsuitable for fiber lasers. Although monocrystalline diamond does not have the above problems, they are more difficult to manufacture.

Over the years, Fraunhofer Institute for Applied Solid State Physics (IAF) has been researching the production of single crystal diamonds. The continuous vapor deposition (CVD) reactor developed by the IAF has a stable plasma characteristic, which is capable of producing substrates up to several millimeters in thickness. More than 60 diamonds can be produced at the same time. At a rate of over 30 microns per hour, the reactor can produce a material having a pore size of about 10 millimeters.

Reduce 90% weight of diamond optical laser head

These synthetic single crystal diamond lenses exhibit low absorption and low birefringence properties. At present, several samples have been tested for anti-reflective coating and are incorporated into the fiber laser cutting head.

"We first optimized the complete laser optics system for diamond lenses," said Martin Traub, from the Fraunhofer Laser Technology Research Institute (ILT). "For this reason, the weight of the cutting head is reduced by almost 90%."

The diameter of 7mm lens has passed the 2kW laser power test without any problems. Now, the partners have established a cutting test system with 1kW fiber lasers. The integration in the cutting head is water cooling and protective gas supply, but has not yet been planned for process monitoring. The first test is being performed using a small cutting head.

The new optical system can greatly increase the flexibility of laser cutting. Small size allows the system to handle hard-to-reach areas, while lighter weight facilitates highly dynamic processes in 3D processing.

Luoyang Yuxin Diamond Co., Ltd prepared Chemical Vapor Deposition (CVD) diamond film, which is made by chemical vapor deposition process. It is in transparent after being double sided polished. The regular diameter can be up to more than 120 mm, and its light transmittance can be up to more than 60% when its thickness is 1 mm. As the typical multifunctional material, the diamond provides  high thermal conductivity, high refractive index, radiation resistance, chemical inertness, excellent electrical and mechanical properties, and it is particularly suitable for infrared optical window with 8~12μm long wave. 

In all the infrared optical materials, CVD diamond film is the only material combining light transmission, thermal shock resistance and with high durability to the impact of raindrops and solid particles as well as chemical corrosion. More importantly, the extremely low thermal expansion coefficient and high thermal conductivity makes the diamond with excellent ret resistance. It keeps nice optical performance in high temperature environment, making it the best material for infrared optical windows serving in harsh environment. 

Application: Window materials for high power laser and detector, protective film for optical lens, radiation detectors and missile radome, etc.