A diamond-based approach to ultrapure lasers

Macquarie University researchers have found a way to make ultrapure-frequency lasers based on diamond, avoiding the problems responsible for destabilising and broadening a laser’s frequency.

In a study published in the journal Optica, Dr Oliver Lux and Associate Professor Rich Mildren demonstrated stable single-frequency operation using a simple laser cavity design that would normally be highly susceptible to destabilisation. They placed a diamond at the midpoint of a longstanding wave cavity, a configuration normally considered a worst-case scenario for inducing the instabilities that cause polychromatic behaviour to occur.

“Lasers are often thought of as being highly monochromatic — that is, of a single frequency — but in most cases their spectral purity is corrupted by a destabilising effect referred to as spatial-hole burning,” said Associate Professor Mildren. “This effect causes the laser frequency to chaotically jump between a grouping of many closely spaced lines.

“The problem is avoided in our case by using a light-amplifying medium that relies on stimulated scattering rather than an excited medium that contains energy such as a population inversion.”

Many laser applications require a pure frequency — a need made even more relevant by the current interest in gravitational wave astronomy, which relies on interference of single-frequency laser beams that are high power and ultrastable. According to Associate Professor Mildren, the new study will enable simpler, more robust systems, as well as greater freedoms for laser design.

“And, since the light amplifier ‘engine’ works using a fundamentally different principle to most lasers we are familiar with, a completely different range of materials may be used including those with extraordinary properties such as diamond,” he said. “This promises a method of generating single frequency lasers over a wider choice of wavelengths and with potentially very high power.”

The results are hoped to enable the next generation of lasers required for remote sensing of greenhouse gases, atomic clocks and atom trapping, as well as in gravitational wave astronomy.