Andreas Boes, Sarah Scholten, Clayton Locke, Nicolas Bourbeau Hébert, Emily Ahern, Lachlan Pointon, Benjamin White, Christopher Billington, Ashby Hilton, Montana Nelligan, Jack Allison, Rachel Offer, Elizaveta Klantsataya, Chris Perrella, Sebastian Ng, Jordan Scarabel, Martin O'Conner, Sonya Palmer, Arnan Mitchell, Robert Zhang, Tin Komljenovic, Andre Luiten
We will provide an overview of the advancement in reducing the size of a high-performance portable Rubidium clock. Afterwards, we will discuss strategies on how the photonic integrated circuit technology can be used to further reduce the size, weight and power of the Rubidium clock for future PNT applications.
The first detection of gravitational waves from a binary black hole inspiral by LIGO in September 2015 heralded the beginning of a new age in gravitational wave astronomy. The detection of a binary neutron inspiral in August 2017 and has now opened up a new era of multi-messenger astronomy. To increase the sensitivity of future gravitational wave detectors, a change to cryogenic silicon test masses and an increase in laser power may be required. Silicon is a compelling choice as it has high thermal conductivity at cryo- genic temperatures, which reduces temperature gradients generated by optical absorption. Additionally, at 123 K, its thermal expansion coefficient crosses zero. Thus, near this temperature, thermo-elastic distortion of the mirror surface should be drastically reduced, as would the effect of thermo-elastic noise due to thermodynamic temperature fluctuations. However, the adoption of silicon for the optical substrates would necessitate a shift of operating wavelength from 1064 nm to >1.3 μm where silicon is transparent. While potential wavelengths include ca. 1.55 μm and 2.0 μm, the longer wavelengths may be preferred due to lower scattering loss and coating absorption.
The next-generation gravitational wave detectors aim to enhance our understanding of extreme phenomena in the Universe. The high-frequency sensitivity of these detectors will be maximized by injecting squeezed vacuum states into the detector. However, the performance advantages offered by squeezed state injection can be easily degraded by losses in the system. A significant source of loss is the mode mismatch between optical cavities within the interferometer. To overcome this issue, new actuators are required that can produce a highly spherical wavefront change, with minimal higher order aberrations, whist adding low phase noise to the incident beam.
Gravitational wave detectors rely on the interference of light at the asymmetric port of a Michelson interferometer. The required light sources for these detectors are high power (200 W) with low intensity and frequency noise [1]. These requirements are currently met with the amplification of a monolithic single-frequency Nd:YAG non-planar-ringoscillator (NPRO) [2]. To improve the sensitivity of next generation detectors, cryogenic silicon test masses have been proposed to reduce the thermal coating noise. Laser sources near 2000 nm appear promising as they lie in the silicon transmission window and have reduced absorption in the amorphous silica coatings which reduces the heat-load on the cryogenically cooled mirrors [3]. High power thulium-doped fibre amplifiers provide broad emission in this wavelength range and have previously been demonstrated with high power and narrow linewidths [4]. Suitable thulium NPRO sources are not commercially available and an alternative seed source is required to determine the noise characteristics of these amplifiers.
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