Unprecedented Spectral Purity with the torus 532 laser from Laser Quantum

17 Jul 2014

The torus 532 laser from Laser Quantum exhibits unprecedented spectral purity at 532nm, as recently demonstrated in a Brillouin scattering application, resulting in a longitudinal mode contrast of 1 part in 10¹¹between the primary mode and any sideband.

Brillouin scattering describes the scattering process of an electromagnetic wave (a photon) and a complex, space-and time-varying acoustic mode within a medium, described by phonons. The photon/phonon interaction is inelastic, causing the interacting photon to gain or lose energy. This shift in photon energy (called the Brillouin Shift) resulting from this interaction is tiny and commonly requires a high resolution interferometer to measure it. Such a measurement, however, provides important information about the medium’s bulk properties. Owing to the small energy transfers between photons and acoustic phonons in the medium, Brillouin scattering experiments require a single frequency laser (also known as a single longitudinal mode or SLM laser) with no observable sidebands.

Historically, large and energy-consuming Argon Ion lasers were used as a source for single frequency laser light; nowadays compact and reliable DPSS laser sources, like Laser Quantum’s torus 532 laser, are available. Using intelligent electronics, the torus range of lasers continually tracks its single longitudinal mode position to ensure there is no mode-hop over a wide temperature range (only ±2pm wavelength drift over 20°C) and the torus 532 is the only actively locked SLM laser commercially available. The output power of the torus 532 can be easily controlled via a jog dial on the power supply while the laser emits SLM light over a wide range (from 50% to 100% of the specified power, up to 750mW output power). To be able to measure the Brillouin Shift, however, the spectral purity of the laser is paramount, since any side-bands in the SLM laser will lie in the range of the Brillouin Shift, thereby masking the signal.

To verify the very high spectral purity of a single frequency laser, the light from Laser Quantum’s torus 532 was coupled into the Tandem Fabry-Perot interferometer TFP-1 from JRS Scientific Instruments. It was shown that the torus 532 laser allows the measurement of tiniest frequency shifts because it is a true single frequency laser with sidebands of less than -110 dB

For all the latest information please visit Laser Quantom Torus SLM Whitepaper