Backscatter-immune, polarization managed, all fiber Sagnac sensing interferometer

We propose a new all fiber Mach-Zehnder-Sagnac hybrid interferometer topology for precision sensing. This configuration utilizes a high coherence laser source, mitigates the effects of Rayleigh backscatter and polarization wander, while eliminating scale factor drift. We also present preliminary experimental results, using telecommunications grade single mode fiber and fiber couplers, to demonstrate its principle of operation

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

Pump-probe differencing technique for cavity-enhanced, noise-canceling saturation laser spectroscopy

We present an experimental technique enabling mechanical-noise free, cavity-enhanced frequency measurements of an atomic transition and its hyperfine structure. We employ the 532nm frequency doubled output from a Nd:YAG laser and an iodine vapour cell. The cell is placed in a traveling-wave Fabry-Perot interferometer (FPI) with counter-propagating pump and probe beams. The FPI is locked using the Pound-Drever-Hall (PDH) technique. Mechanical noise is rejected by differencing pump and probe signals. In addition, this differenced error signal gives a sensitive measure of differential non-linearity within the FPI.Comment: 3 pages, 5 figures, submitted to Optics Letter

Quantum noise limited interferometry

A small bench top interferometer, built to study modulation interferometry is described. A number of different interferometer configurations are trialed, all using a continuos wave, Nd:YAG laser. The ability of these configurations to operate at the shot noise limit is documented and technical noise sources that detract from this limit are investigated. The frequency and intensity noise properties of the Nd:YAG laser, used throughout this work, are documented. It is shown that the free running laser has considerable frequency noise structure from DC to approximately 100kHz. The effects of this frequency noise on interferometry are documented and means of overcoming these problems discussed. The free running laser is shown to exhibit strong intensity noise structure associated with the resonant relaxation oscillation present in the lasing crystal. The resonant relaxation oscillation is modelled by a noise-driven second order system. This description is used to design an intensity stabilisation servo to suppress the free running laser noise. The performance of the stabilisation system is documented and its ability to suppress laser intensity noise by up to 35dB across a wide bandwidth is demonstrated. A simple scalar theory, to describe modulation interferometry is developed. All necessary non-ideal parameters are included and accurate predictions of practical interferometer sensitivity are made. The theory is used to analyse the performance of all interferometers tested here. Bench top interferometer experiments are performed for direct detection, internal modulation, external modulation and power recycling interferometer configurations. The shot noise sensitivity of each configuration is measured and excellent agreement with theory is achieved. An application for the direct detection interferometer is demonstrated; noninvasive shot noise limited RF electric field measurements. Several circuit boards are mapped using this device and the results presented. Non-stationary shot noise in internal modulation interferometers is investigated. Using a large modulation depth and high fringe visibility interferometer, approximately 4.8dB of noise variation dependent on the demodulation phase is achieved. Non-stationary shot noise is shown to cause excess noise (1.7dB) in the signal quadrature, leading to shot noise limited sensitivity of √ (3/2) worse than direct detection. A complex modulation-demodulation system is then implemented using both the first and third harmonic. The addition of the third harmonic is shown to introduce correlated shot noise that can be used to reduce the excess 1.7dB nonstationary shot noise occurring in the signal quadrature

Experimental demonstration of a classical analog to quantum noise cancellation for use in gravitational wave detection

We present results that are a classical analog to quantum noise cancellation. It is possible to breach the standard quantum limit in an interferometer by the use of squeezing to correlate orthogonal quadratures of quantum noise, causing their effects on the resulting sensitivity to cancel. A laser beam incident on a Fabry-Perot cavity was imprinted with classical, correlated noise in the same quadratures that cause shot noise and radiation pressure noise. Couplings between these quadratures due to a movable mirror, sensitive to radiation pressure, cause the excess classical noise to cancel. This cancellation was shown to improve the signal to noise ratio of an injected signal by approximately a factor of 10

Cooling of a gram-scale cantilever flexure to 70 mK with a servo-modified optical spring

A series of recent articles have presented results demonstrating optical cooling of macroscopic objects, highlighting the importance of this phenomenon for investigations of macroscopic quantum mechanics and its implications for thermal noise in gravitational wave detectors. In this Letter, we present a measurement of the off-resonance suspension thermal noise of a 1 g oscillator, and we show that it can be cooled to just 70 mK. The cooling is achieved by using a servo to impose a phase delay between oscillator motion and optical force. A model is developed to show how optical rigidity and optical cooling can be interchangeable using this technique

Squeezing in the audio gravitational wave detection band

We demonstrate the generation of broad-band continuous-wave optical squeezing down to 200Hz using a below threshold optical parametric oscillator (OPO). The squeezed state phase was controlled using a noise locking technique. We show that low frequency noise sources, such as seed noise, pump noise and detuning fluctuations, present in optical parametric amplifiers have negligible effect on squeezing produced by a below threshold OPO. This low frequency squeezing is ideal for improving the sensitivity of audio frequency measuring devices such as gravitational wave detectors.Comment: 5 pages, 6 figure

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