We demonstrate a robust, stable and compact spectral filter for use in quantum optics experiments by implementing Fabry-Pérot resonators within optical fibre using pairs of fibre Bragg gratings. With only temperature stabilisation, these devices show less than 20 MHz frequency drift over 12 hours with a maximum suppression of roughly 35 dB and overall transmission of 75%. These characteristics make fibre Bragg grating Fabry-Pérot resonators ideal for quantum optics experiments where single photon-level signals must be efficiently filtered from large optical fields.
Atom-Trap Trace-Analysis (ATTA) is a technique aimed at a measuring the relative (in comparison to the common isotope) abundance of exceedingly rare noble gas radio-isotopes (Ar-39, Kr-81 and Kr-85), for the purposes of dating water, ice and other materials that contain trapped gases. These isotopes exist with an extremely low natural abundance and require measurement capability down to parts in 1017. The noble gas dating protocol is similar to that of radio-carbon dating but, the three isotopes together, allow dating of materials in complementary ranges to that possible with the radiocarbon technique. In a facility jointly created by CSIRO, Griffith and Adelaide Universities, we use laser guidance, cooling and trapping to perform isotopic separation using the isotopic dependence of atomic energy levels. The facility is currently undergoing construction but has been shown to be able to produce metastable Ne and Ar, which can then be laser cooled and trapped. When combined with the existing gas separation facility at the CSIRO Waite facility, which efficiently extracts pure noble gases from that are dissolved in water or ice samples, we should be in a position to start measuring the age of real-world samples in the early part of 2020. In addition, to describing the current state of construction, we will also discuss two more efficient approaches for creating metastable atoms that can reduce samples size and avoid unwanted cross-contamination between samples.
We have shown that it is possible to injection lock a pulsed Vertical Cavity Surface Emitting Laser (VCSEL). This is a cheap source of nanosecond pulsed light with a background noise of approximately ten percent. An inexpensive source of narrow-band pulsed light such as this could find many uses in quantum optics, such as the development of highbandwidth quantum memory.
The rapid measurement of gas concentrations is beneficial to a broad range of applications, including pollution monitoring, high-precision spectroscopy, and medical breath analysis. Optical frequency combs (OFCs) are a near-ideal optical interrogation source for molecular spectroscopy, combining broadband light with high frequency-precision and dense spectral sampling, characteristics which also allow short measurement times. A spectrometer based on a virtually imaged phased array (VIPA) is used to unravel the comb into a high-resolution transmission spectrum, with the returned spectra rapidly fitted with a detailed spectral model for concentration extraction of CO2. We demonstrate an accuracy of 0.5% and 12% for concentration measurements of 12C16O2 and 13C16O2 respectively, with the measured isotopic ratio in excellent agreement with that expected from their natural abundances. Precision of the concentration measurements is also high, at 0.03% and 1.24% for 12C16O2 and 13C16O2 respectively. The measurement technique is also verified to be highly linear for concentrations ranging over three orders of magnitude. The spatial and temporal coherence of OFCs additionally enables the use of the full range of performance-enhancing optical techniques including resonant enhancement. Here we demonstrate the use of a multi-pass Herriott cell to enhance the effective measurement path length, which allows the continuous optical measurement of CO2 production during the respiration of baker’s yeast in a closed system. Results from the yeast experiments agree well with existing literature.
We have studied the bandwidth of atomic magnetometers based on nonlinear magneto-optical rotation (NMOR). We demonstrated broadband, high-bandwidth magnetic field measurements from DC up to 100kHz with two different techniques. The first technique measures the instantaneous phase evolution of the optical polarisation rotation in the temporal domain which enabled quantitative measurements of modulated magnetic fields up to 100kHz for a carrier frequency of 30kHz, while the second method employs active feedback techniques to track magnetic field fluctuations up to 100kHz, approximately 2800-fold greater than the passive bandwidth. For the latter case, a slew rate of 91.4nT/μs and a sensitivity of 200fT/Hz1/2 around 8Hz have been achieved at a bias field of 50μT.
Presently, among the most demanding applications for highly sensitive magnetometers are Magnetocardiography (MCG) and Magnetoencephalography (MEG), where sensitivities of around 1pT.Hz-1/2 and 1fT.Hz-1/2 are required. Cryogenic Superconducting Quantum Interference Devices (SQUIDs) are currently used as the magnetometers. However, there has been some recent work on replacing these devices with magnetometers based on atomic spectroscopy and operating at room temperature. There are demonstrations of MCG and MEG signals measured using atomic spectroscopy These atomic magnetometers are based on chip-scale microfabricated components. In this paper we discuss the prospects of using photonic crystal optical fibres or hollow core fibres (HCFs) loaded with Rb vapour in atomic magnetometer systems. We also consider new components for magnetometers based on mode-locked semiconductor lasers for measuring magnetic field via coherent population trapping (CPT) in Rb loaded HCFs.