High-Power Unique-Stability Laser Source For Quantum Applications

UCL will characterise the noise characteristics of the amplification of the Mephisto laser system in Yb fibre amplifiers. Our group at UCL regularly use low noise laser systems (including the Mephisto) to provide a stable high laser source for trapping and cooling of atoms, molecules and nanoparticles. As our experiments are particularly sensitive to laser noise they offer an ideal testbed for this laser system. To test the system, one of the lasers outputs will be locked to a narrow external cavity resonance while the other is detuned from this frequency at a well- defined GHz frequency shift. We will test to verify that the frequency of the locking laser will be able to rapidly follow thermal, mechanical and acoustic frequency drifts in the high finesse cavity. The second output of the laser will be tested to understand how well it will follow the same frequency modulations as the cavity locking output. To characterise the capabilities of this system we will measure the phase and amplitude noise and its probable effects on trapping and optomechanics experiments. This type of experiment is particularly sensitive to laser noise due to the large mass of the oscillator (10^-17 kg) when compared to our atomic argon trapping experiments. Currently this system is cooled down to milliKelvin centre-of-mass temperatures by cavity cooling methods. Here the Mephisto will be directly locked to a higher order TEM mode of the cavity while the second fibre amplified component will be used to provide the high power cooling beam that is frequency offset by 1.3 GHz from the main laser output. This beam will be red-detuned from the adjacent TEM00 resonance by up to 100 kHz. The frequency stability of all outputs must be better than 1 kHz. The noise in the amplifier must be ideally maintained at the same level of the Mephisto. All data will be shared with Coherent, and regular discussions will be held before the planned experiments to make sure the system is on target to meet the requirements for these types of experiments.

The laser system that Coherent, in collaboration with UCL, will develop will have significant impact on a large range of
future and present quantum technologies. Lasers with high power and low noise are critical to a range of quantum
technologies that utilise cold atoms for cooling and trapping but also for a range of fundamental work that supports these.
The high power and low noise output are required to prevent loss of atoms while they are being trapped. These will benefit
a wide range of academic and industrial endeavours that are developing inertial sensing (accelerometers, gravimeters and
gyros), time and frequency standards (lattice atomic clocks) and magnetometry. The low noise of this system will benefit
the growing range of engineered quantum optomechanics applications that are being developed worldwide. For example
we are currently developing an optomechanics based accelerometer (funded from other government sources) that will
directly benefit from the low noise promised by this system. In addition to quantum technologies this laser system will find
applications in both optical metrology and in gravitational wave research.