Suppression of Classical and Quantum Radiation Pressure Noise via Electro-Optic Feedback

We present theoretical results that demonstrate a new technique to be used to improve the sensitivity of thermal noise measurements: intra-cavity intensity stabilisation. It is demonstrated that electro-optic feedback can be used to reduce intra-cavity intensity fluctuations, and the consequent radiation pressure fluctuations, by a factor of two below the quantum noise limit. We show that this is achievable in the presence of large classical intensity fluctuations on the incident laser beam. The benefits of this scheme are a consequence of the sub-Poissonian intensity statistics of the field inside a feedback loop, and the quantum non-demolition nature of radiation pressure noise as a readout system for the intra-cavity intensity fluctuations.Comment: 4 pages, 1 figur

Control and tuning of a suspended Fabry-Perot cavity using digitally-enhanced heterodyne interferometry

We present the first demonstration of real-time closed-loop control and deterministic tuning of an independently suspended Fabry-Perot optical cavity using digitally-enhanced heterodyne interferometry, realising a peak sensitivity of $\sim$10 pm$/\sqrt{\mathrm{Hz}}$ over the 10-1000 Hz frequency band. The methods presented are readily extensible to multiple coupled cavities. As such, we anticipate that refinements of this technique may find application in future interferometric gravitational-wave detectors

Sensing and control in dual-recycling laser interferometer gravitational-wave detectors

We introduce length-sensing and control schemes for the dual-recycled cavity-enhanced Michelson interferometer configuration proposed for the Advanced Laser Interferometer Gravitational Wave Observatory (LIGO). We discuss the principles of this scheme and show methods that allow sensing and control signals to be derived. Experimental verification was carried out in three benchtop experiments that are introduced. We present the implications of the results from these experiments for Advanced LIGO and other future interferometric gravitational-wave detectors

Arm-length stabilisation for interferometric gravitational-wave detectors using frequency-doubled auxiliary lasers

Residual motion of the arm cavity mirrors is expected to prove one of the principal impediments to systematic lock acquisition in advanced gravitational-wave interferometers. We present a technique which overcomes this problem by employing auxiliary lasers at twice the fundamental measurement frequency to pre-stabilise the arm cavities' lengths. Applying this approach, we reduce the apparent length noise of a 1.3 m long, independently suspended Fabry-Perot cavity to 30 pm rms and successfully transfer longitudinal control of the system from the auxiliary laser to the measurement laser

Measuring coalignment of retroreflectors with large lateral incoming-outgoing beam offset

A method based on phase-shifting Fizeau interferometry is presented with which retroreflectors with large incoming-outgoing beam separations can be tested. The method relies on a flat Reference Bar that is used to align two auxiliary mirrors parallel to each other to extend the aperture of the interferometer. The method is applied to measure the beam coalignment of a prototype Triple Mirror Assembly of the GRACE Follow-On Laser Ranging Interferometer, a future satellite-to-satellite tracking device for Earth gravimetry. The Triple Mirror Assembly features a lateral beam offset of incoming and outgoing beam of 600 mm, whereas the acceptance angle for the incoming beam is only about ±2 mrad. With the developed method, the beam coalignment of the prototype Triple Mirror Assembly was measured to be 9 μrad with a repeatability of below 1 μrad

Towards solid-state beam steering using a 7-emitter 1550 nm optical phased array

We present the preliminary design and experimental results of a 1550 nm solid-state beam pointing system based on an optical phased array (OPA) architecture. OPAs manipulate the distribution of optical power in the far-field by controlling the phase of individual emitters in an array. This allows OPAs to steer the beam in the far field without any mechanical components (e.g., steering mirrors). The beam-steering system presented here uses waveguide electro-optic modulators to actuate the phase of each element in a 7-emitter OPA, enabling kHz bandwidth steering with sub-milliradian pointing precision. The control system used to stabilize and control the phase of each emitter in the OPA exploits a technique called digitally enhanced heterodyne interferometry, allowing the phase of each emitter to be measured simultaneously at a single photodetector, dramatically simplifying the optical system. All digital signal processing is performed using a field-programmable gate-array. Applications of this technology include free-space link acquisition and tracking for satellite-to-satellite laser communications and light detection and ranging (LiDAR).This work was partially funded by the Australian Research Council Centre of Excellence for Gravitational Wave Discovery (OzGrav) (project ID CE170100004) and the Australian Research Council Centre of Excellence for Engineered Quantum Systems (EQUS) (project ID CE170100009)

Pico-strain multiplexed fiber optic sensor array operating down to infra-sonic frequencies

An integrated sensor system is presented which displays passive long range operation to 100 km at pico-strain (pε) sensitivity to low frequencies (4 Hz) in wavelength division multiplexed operation with negligible cross-talk (better than −75 dB). This has been achieved by prestabilizing and multiplexing all interrogation lasers for the sensor array to a single optical frequency reference. This single frequency reference allows each laser to be locked to an arbitrary wavelength and independently tuned, while maintaining suppression of laser frequency noise. With appropriate packaging, such a multiplexed strain sensing system can form the core of a low frequency accelerometer or hydrophone array

Progress in Interferometry for LISA at JPL

Recent advances at JPL in experimentation and design for LISA interferometry include the demonstration of Time Delay Interferometry using electronically separated end stations, a new arm-locking design with improved gain and stability, and progress in flight readiness of digital and analog electronics for phase measurements.Comment: 11 pages, 9 figures, LISA 8 Symposium, Stanford University, 201