Laser monitor for imaging single crystal diamond growth in H2-CH4 microwave plasma

•CuBr-laser monitor is used for imaging a growing diamond crystal in microwave plasma of CVD reactor.•Contrast images of diamond surface through H2-CH4 plasma background radiation.•The optical configuration provides 4 × 4 mm2 field of view with spatial resolution up to 30 µm. We used an active optical system referred to as ‘laser monitor’ based on a copper bromide vapor brightness amplifier for imaging a diamond crystal surface during its synthesis in a microwave plasma in CH4-H2 gas mixture. The approach allows observation of an entire crystal without interrupting the chemical vapor deposition process. It is demonstrated that the broadband plasma background radiation with the brightness temperature of about 3000 K does not interfere with object real-time monitoring at the laser wavelength of 510.6 nm. High quality images obtained using both passive (laser illumination) and active (laser monitor) methods provide information about the surface relief of the growing crystal with resolution of a few tens of micrometer. Each frame is formed through one pulse (about 30 ns), with the maximum frame rate being 20,000 frames/sec.