Technology
Our engineering platform utilizes the spectrum discriminatory feature of a Michelson interferometer setup within a spectral range preselected by a VBG. This suppresses all but one lasing longitudinal mode within the laser cavity. Due to significantly lower power consumption and simplified thermal management, BRaMMS-based lasers provide improved output power scalability from a remarkably small footprint.
The technology at the core of our single frequency DPSS lasers is the culmination of decades of research.
We have sought to dramactically improve the performance of SLM DPSS lasers through the incorporation of a VBG within a typical Michelson interferometer arrangement. The result of this is the ability to preselect the spectral range of the laser.
Since the isolation and selection of the single frequency is managed by the VBG/Michelson arrangement, the only source of variation is the length of the cavity itself. It is therefore critical for optimum operation that the position of the end cavity mirrors and the temperature of the cavity are monitored and controlled.
All critical components are controlled by Peltier cooling to minimise any variation caused by external temperature fluctuations. High stability is easily achieved by one final aspect of the design: a small amount of leakage is allowed from the Michelson, falling onto a split diode, part of a feedback loop to the PZT mounted end mirrors.
The use of the Michelson arrangement ensures absolute single frequency of operation, with standard linewidths below 500 kHz, giving coherence lengths well in excess of 100m and free-running frequency drift as low as 1pm over 4 hours and an ambient temperature drift of 5°C. This stability can be further increased by the use of active heat sinks that maintain the baseplate temperature during laser operation.
Some applications such as atom cooling or acting as the clock laser in an optical clock demand higher levels of stability and even narrower linewidths. This can be achieved with the BRaMMS Technology® QT range of lasers designed specifically for this quantum devices. The feedback loop for the end cavity mirrors is handed over to external electronics allowing a simple “tilt-locking” technique to adjust the PZT-controlled mirrors, without application of modulation on the output beam.
The result is line narrowing to below 100 kHz, with an eventual target of a few tens of kHz, and output frequency stability that is limited by the external reference.
DPSS
diode-pumped solid state, in reference to the means of acheiving population inversion in a solid gain medium of a laser
SLM
single longitudinal mode
VBG
volume Bragg grating, a diffraction grating in which there is a periodic modulation of the refractive index through the entire volume of a photosensitive material
Peltier cooling
a solid-state active heat pump which transfers heat from one side of the device to the other, with consumption of electrical energy
PZT
lead zirconate titanate, an inorganic compound with marked piezoelectric properties