High-sensitivity Interferometer Research Articles

High-Sensitivity Quantum-Enhanced Interferometers

High-sensitivity interferometers are one of the basic tools for precision measurement, and their sensitivity is limited by their shot noise limit (SNL), which is determined by vacuum fluctuations of the probe field. The quantum interferometer with novel structures can break the SNL and measure the weak signals, such as the direct observation of gravity wave signal. Combining classical interferometers and the optical parametric amplifier (OPA) can enhance the signal; meanwhile, the quantum noise is kept at the vacuum level, so that the sensitivity of the nonlinear interferometer beyond the SNL can be achieved. By analyzing in detail the influence of system parameters on the precision of quantum metrology, including the intensity of optical fields for phase sensing, the gain factor of OPA, and the losses inside and outside the interferometers, the application conditions of high-sensitivity nonlinear quantum interferometers are obtained. Quantum interferometer-based OPAs provide the direct references for the practical development of quantum precise measurement.

All-fiber millimeter-scale M-Z interferometer based on slow light in microknot resonator

High sensitivity interferometers are key building blocks in many areas of optical and photonic devices. In this letter, we propose and experimentally demonstrate a new scheme for improving the phase sensitivity of interferometer by using slow light in a microknot resonator (MKR). The slow-light interferometer with a footprint of 1.5 mm × 4 mm is fabricated by using microfiber with a diameter of 5.6 μm. By coupling MKR to one arm of the interferometer, the slow light is introduced to enhance the phase sensitivity of the interferometer. The experimental results show that the MKR has a Q-factor of 13520, and the time delay of slow light at resonance frequency is 28 ps. The phase sensitivity of Mach-Zehnder interferometer(MZI) with slow light is 25.54 rad/THz, which is 10.4 times that of a MZI without slow light. The proposed hybrid structure has the advantages of easy fabrication, small footprint, high sensitivity and wide slow light bandwidth, allowing for potential applications in miniaturization of spectrometer and high sensitivity sensing.

A search for cool molecular gas in GK Persei and other classical novae

Detecting molecular line emission from classical nova remnants has the potential to reveal information on the composition of the ejecta, in particular accurate isotopic ratios in the matter processed by a thermonuclear runaway. We conducted searches toward more than 100 classical novae for emission in lines of CO or HCN molecules using single-dish telescopes and interferometric arrays at millimeter and submillimeter wavelengths. The survey demonstrates that classical novae, young or old, are not strong sources of molecular emission at submillimeter or millimeter wavelengths. Additionally, we mapped CO emission around Nova Persei 1901 (GK Per), earlier claimed to be of circumstellar origin. Our measurements indicate that the observed emission is from the interstellar medium. Although no molecular emission at millimeter or submillimeter wavelengths has been found in classical novae, it is still likely that some will be detected with high-sensitivity interferometers such as ALMA.

Search for grain growth toward the center of L1544

In dense and cold molecular clouds dust grains are surrounded by thick icy mantles. It is however not clear if dust growth and coagulation take place before the switch-on of a protostar. This is an important issue, as the presence of large grains may affect the chemical structure of dense cloud cores, including the dynamically important ionization fraction, and the future evolution of solids in protoplanetary disks. To study this further, we focus on L1544, one of the most centrally concentrated pre-stellar cores on the verge of star formation, and with a well-known physical structure. We observed L1544 at 1.2 and 2 mm using NIKA, a new receiver at the IRAM 30 m telescope, and we used data from the Herschel Space Observatory archive. We find no evidence of grain growth towards the center of L1544 at the available angular resolution. Therefore, we conclude that single dish observations do not allow us to investigate grain growth toward the pre-stellar core L1544 and high sensitivity interferometer observations are needed. We predict that dust grains can grow to 200 $\mu$m in size toward the central ~300 au of L1544. This will imply a dust opacity change by a factor of ~2.5 at 1.2 mm, which can be detected using the Atacama Large Millimeter and submillimeter Array (ALMA) at different wavelengths and with an angular resolution of 2".

A microwave interferometer for small and tenuous plasma density measurements

The non-intrusive density measurement of the thin plasma produced by a mini-helicon space thruster (HPH.com project) is a challenge, due to the broad density range (between 10(16) m(-3) and 10(19) m(-3)) and the small size of the plasma source (2 cm of diameter). A microwave interferometer has been developed for this purpose. Due to the small size of plasma, the probing beam wavelength must be small (λ = 4 mm), thus a very high sensitivity interferometer is required in order to observe the lower density values. A low noise digital phase detector with a phase noise of 0.02° has been used, corresponding to a density of 0.5 × 10(16) m(-3).

Two-beam interferometer with optical path difference magnified

A two-beam interferometer is proposed and experimentally demonstrated with OPD magnified. Two cascaded fiber ring resonators with almost the same fiber length are spliced into a fiber loop. An acousto-optic modulator is employed to generate optical pulses and to choose the pulses traveling around one of the resonators for x trips. The interferometer is characterized in displacement in our experiment. Experimental results show the proportional relationship between the sensitivity and x. The high-sensitivity interferometer scheme is useful in some measurement applications that require high sensitivity, such as solid earth tide gauge.

Slow and fast light: basic concepts and recent advancements based on nonlinear wave‐mixing processes

AbstractAfter a review of the basic concepts of slow and fast light, recent advancements based on nonlinear wave‐mixing processes are described. As a nonlinear medium, the authors focus on a liquid crystal light valve showing that it allows obtaining a large control of the group delay, with a maximum fractional delay of 1, and a deceleration of light pulses down to group velocities as small as 0.2 mm/s. A theoretical model accompanies the observations and accounts for them in the general framework of two‐wave mixing in the light valve. At the end, a high‐sensitivity interferometer is presented as an example of slow light applications.

Improvements at low frequency in the interferometric test of the suspensions of the Virgo gravitational wave antenna

A high sensitivity interferometer has been used to test the suspension of the Virgo interferometric antenna for gravitational wave search. Since Virgo is planning to enlarge the detection window down to 10 Hz, particular care is taken to improve the sensitivity in the low frequency region. Noise spectra are discussed. Between 20 and 100 Hz the limiting noise is of the order of 10 −14 m Hz , and it reaches 10 −15 m Hz above 100 Hz. Above 10 kHz the interferometer sensitivity is shot noise limited.

A sensitive He–Ne interferometer with passive beam power stabilization for low-density pulsed-plasma measurements

A sensitive interferometer based on a Michelson scheme was constructed and applied to low-density pulsed-plasma measurements. Using a moderate power He–Ne laser and common photodetectors, a sensitivity as high as 1/1000 FWHM of an interference fringe was reached with a minimum line-integrated plasma density as low as 〈NeL〉min=8×1013 cm−2. This sensitivity was obtained in a real plasma experiment with space and time resolution of 1–2 mm and 120 ns, respectively. The time resolution for this technique is restricted mainly by the oscilloscope finite input capacitance and could be made higher but with a loss of sensitivity. In order to obtain such high a sensitivity, we used loads for the photocurrent registration higher than the 50-Ω matched load. The initial phase is not assumed to be optimized and is recorded separately during the operation of the interferometer. Suppression of electrical noise and of instabilities associated with the laser power requires a supplementary detector for background subtraction to improve the signal-to-noise ratio. A description of the high sensitivity interferometer with the passive beam power stabilization, analysis of the data treatment procedure, as well as measurements for an electron density distribution, are presented.

Optical boundary-layer transition detection in a transonic wind tunnel

A high-sensitivity interferometer has been developed and used to detect boundary-layer transitions over a symmetric airfoil. The tests, which included both natural and roughness-induced transitions, were performed in a transonic wind tunnel. The measurements showed a peak amplitude rms and higher energy in the spectrum of the signal associated with transition. The tests revealed that the interferometer system can be used to locate the transition region over three-dimensional aerodynamic models.

Precise and versatile systems for dilatometric measurement of solid materials

An interferometric dilatometer has been developed which uses a double path high-sensitivity interferometer and specimen supporting systems. Usual interferometric dilatometers require polished specimens, but the present system does not need any special specimen preparation. The system, therefore, provides measurement facilities for various shapes and dimensions of materials such as thin wires, slender rods, etc. The interferometric system incorporates self-compensation for optical misalignment and a resolution of 1 nm can be achieved by using an ac fringe detecting system.