Retroreflecting Mirror Research Articles

Spontaneously Sliding Multipole Spin Density Waves in Cold Atoms.

We report on the observation of spontaneously drifting coupled spin and quadrupolar density waves in the ground state of laser driven Rubidium atoms. These laser-cooled atomic ensembles exhibit spontaneous magnetism via light mediated interactions when submitted to optical feedback by a retroreflecting mirror. Drift direction and chirality of the waves arise from spontaneous symmetry breaking. The observations demonstrate a novel transport process in out-of-equilibrium magnetic systems.

All reflective FROG using near 90° retro-reflecting mirror for single shot intensity and phase profile measurement of ultra-short laser pulse

In this paper, we propose a novel scheme for an all-reflective FROG device using a near-90° retro-reflecting mirror for the complete single-shot measurement of intensity and phase of ultra-short laser pulses. The proposed device has several advantages, such as (1) it is an all-reflective setup, hence no added material dispersion; (2) it is simple and free from alignment disturbances; and (3) the temporal resolution and temporal range of the device can be tuned as per requirement. The proposed device was set up to measure mode-locked ultra-short laser pulses generated from a Ti:Sapphire laser oscillator. Dispersion-broadened laser pulses, obtained by passing the oscillator pulses through a 30 cm long Nd:glass rod, were also characterized, and the group velocity dispersion parameter value of the glass rod was estimated.

A 90° retro-reflecting mirror based autocorrelator for temporal duration and pulse front tilt measurements of ultra-short laser pulse

A 90° retro-reflecting mirror based autocorrelator for temporal duration and pulse front tilt measurements of ultra-short laser pulse

Optimization and control of cold atom interference phase shift based on laser double-sideband suppression

Using the electro-optical modulation method to generate Raman beams for cold atom interference is one of the better methods for constructing a more compact and robust laser system. But this way will generate some residual sidebands resulting in the additional interference phase shift, which can affect the measurement accuracy of cold atom interferometer. In order to weaken the effect of laser modulation sidebands on the phase shift of cold atom interference, a double-sideband suppressed-carrier modulation laser system for cold atom interference is constructed. Based on the designed laser system, the principle of double-sideband generation and suppression is analyzed in detail, and some residual sidebands are adjusted and controlled. Moreover, some important optical parameters that affect the phase shift of cold atomic interference, such as the initial distance between the Raman retro-reflection mirror and the atomic cloud, the interrogation time between two adjacent Raman pulses, the laser modulation depth and the initial velocity of the atomic cloud, are discussed and optimized. By optimizing these relevant parameters, the influence of residual modulation sidebands on the phase shift of cold atomic interference is weakened drastically. The research results indicate, making use of the method of double-sideband suppression, the phase shift of cold atomic interference can be optimized to 0.7 mrad when the initial distance between the Raman retro-reflection mirror and the atomic cloud is 105 mm, and the interrogation time between two adjacent Raman pulses is 82 ms. More importantly, this work can provide a method for weakening the influence of Raman sideband effect on the phase shift of cold atom interferometer, and the corresponding laser system can be applied to other inertial sensors such as atomic gravimeter or atomic gravity gradiometer.

Compact Active Vibration Isolation and Tilt Stabilization for a Portable High-Precision Atomic Gravimeter

In high-precision atomic gravimeters, a rest mass is needed to provide a gravity reference, which is typically the retro-reflecting mirror of the Raman laser beams that addresses the two hyperfine ground states of the specific free-falling atomic test mass. We constructed a compact active feedback control system for the retro-reflecting mirror that provides vibration isolation in the vertical axis as well as two rotation stabilization in the horizontal plane. The active feedback control provides vertical vibration reduction of up to a factor of 300 in the frequency range of 0.03 to 10 Hz and tilt stabilization of approximately $\pm$ 1 $\mu$rad in the noisy lab environment. This system has enabled high-precision gravity measurements on a portable gravimeter with sensitivity reaching $6.4\times 10^{-8}$ g/$\sqrt{\text{Hz}}$ and resolution of $2.8\times 10^{-9}$ g after an integration time of 4000 s.

Sensitive quantum tiltmeter with nanoradian resolution

Precision tilt measurements are becoming more and more important in fundamental research and crustal deformation observations. A quantum tiltmeter based on atom interferometry could be among the most stable tiltmeters in theory but is currently constrained by the low resolution. Here, we demonstrate an extremely sensitive quantum tiltmeter with the configuration of a Mach-Zehnder-type atom interferometer for precisely measuring the crustal deformation. The scheme of two pairs of Raman beams sharing one retroreflection mirror effectively increases the scale factor, making this quantum tiltmeter achieve a sensitivity of $40\phantom{\rule{0.28em}{0ex}}\mathrm{nrad}/{\mathrm{Hz}}^{1/2}$ and a resolution of 1.8 nrad within an integration time of 640 s for tilt measurements, which represents an improvement on the sensitivity by a factor of 32 comparing to previous work. The Earth tilt tide lasting for 63 h has been observed with high signal-to-noise ratio by our quantum tiltmeter, which paves the way to study the crustal deformation with a quantum sensor.

Velocity measurements in a supersonic wind tunnel with a novel calibration-free seedless velocimetry utilizing laser-induced shockwaves and a double-line probe system

A novel calibration-free seedless velocimetry technique utilizing a shockwave generated by a laser-induced plasma (LIP) is proposed and used for measuring velocity profile in a supersonic flow. A nanosecond laser pulse of 532-nm wavelength is focused in the test section of a supersonic wind tunnel to generate the LIP that emanates a shockwave. A continuous-wave laser beam of 658-nm wavelength traverses the region adjacent to the LIP twice between a knife-edge mirror and a retroreflecting mirror. The probe beam is monitored by a fast photodiode after the second reflection from the knife-edge mirror, to record the arrival of the LIP shockwaves at the two probe beam locations; the laser beam deflects when the shockwave reaches the beam, and this deflection is registered on the photodiode signal read by an oscilloscope. It is shown that the shockwave-arrival time is highly sensitive to the convection speed of the flow that carries the shockwave. An empirical point-explosion blast model, determining time-dependent shockwave location, is used to calculate the average convection velocity between the LIP and the farthest probe beam 4.5 mm from the LIP with a precision of better than 8 m/s (1.5%). The empirical model contains two coefficients, a shockwave-propagation coefficient and the flow velocity, which are determined by the shockwave-arrival times and the locations of the two probe beams relative to the LIP. The LIP is positioned along a span-wise direction of the supersonic wind tunnel to measure the velocity profile; the probe beams are parallel with the spanwise direction. Uniform flow velocity is found within the core-flow of the wind tunnel, which well agrees with the velocity estimated by the pressure and temperature measured in the tunnel.

Self-Organization in Cold Atoms Mediated by Diffractive Coupling

This article discusses self-organization in cold atoms via light-mediated interactions induced by feedback from a single retro-reflecting mirror. Diffractive dephasing between the pump beam and the spontaneous sidebands selects the lattice period. Spontaneous breaking of the rotational and translational symmetry occur in the 2D plane transverse to the pump. We elucidate how diffractive ripples couple sites on the self-induced atomic lattice. The nonlinear phase shift of the atomic cloud imprinted onto the optical beam is the parameter determining coupling strength. The interaction can be tailored to operate either on external degrees of freedom leading to atomic crystallization for thermal atoms and supersolids for a quantum degenerate gas, or on internal degrees of freedom like populations of the excited state or Zeeman sublevels. Using the light polarization degrees of freedom on the Poincaré sphere (helicity and polarization direction), specific irreducible tensor components of the atomic Zeeman states can be coupled leading to spontaneous magnetic ordering of states of dipolar and quadrupolar nature. The requirements for critical interaction strength are compared for the different situations. Connections and extensions to longitudinally pumped cavities, counterpropagating beam schemes and the CARL instability are discussed.

Self-bound droplet clusters in laser-driven Bose-Einstein condensates

We investigate a two-dimensional Bose-Einstein condensate that is optically driven via a retro-reflecting mirror, forming a single optical feedback loop. This induces a peculiar type of long-range atomic interaction with highly oscillatory behavior, and we show here how the sign of the underlying interaction potential can be controlled by additional optical elements and external fields. This additional tunability enriches the behavior of the system substantially, and gives rise to a surprising range of new ground states of the condensate. In particular, we find the emergence of self-bound crystals of quantum droplets with various lattice structures, from simple and familiar triangular arrays to complex superlattice structures and crystals with entirely broken rotational symmetry. This includes mesoscopic clusters composed of small numbers of quantum droplets as well as extended crystalline structures. Importantly, such ordered states are entirely self-bound and stable without any external in-plane confinement, having no counterpart to other quantum-gas settings with long-range atomic interactions.

Complex spatiotemporal coupling distortion pre-compensation with double-compressors for an ultra-intense femtosecond laser.

In an ultra-intense femtosecond chirped-pulse amplification laser, the imperfect diffraction wave-fronts of the second and the third gratings of the compressor, where spatio-spectral coupling exists, could introduce a complex spatiotemporal coupling distortion (STCD) and degrade the pulsed beam in both near- and far-fields. Here, we propose a method of double-compressors for pre-compensation. By inserting a scaled down compressor (small compressor) with a deformable retro-reflection mirror into the beam-line, the frequency-dependent wave-front distortion, i.e., the complex STCD, could be removed. We simulate the results in two different ultra-intense femtosecond lasers with 80 and 400 nm bandwidths for comparison, and near ideal focused peak intensities could be obtained in both cases. Meanwhile, the influences of several miss-matching effects, which might appear in engineering, are also analyzed and discussed for applications.

Analysis of Quality Improvement of a Floating Image Using a Hybrid Retroreflective Mirror Array Sheet

Analysis of Quality Improvement of a Floating Image Using a Hybrid Retroreflective Mirror Array Sheet

Inversion-symmetry breaking in spin patterns by a weak magnetic field

Laser driven cold atoms near a plane retro-reflecting mirror exhibit self-organization above a pump threshold. We analyze the properties of self-organized spin patterns in the ground state of cold rubidium atoms. Antiferromagnetic patterns in zero magnetic field give way to ferrimagnetic patterns if a small longitudinal field is applied. We demonstrate how the experimental system can be modeled as spin-1 atoms diffractively coupled by the light reflected by the mirror. The roles of both dipolar and quadrupolar magnetization components in determining the threshold and symmetry variations with a weak longitudinal magnetic field are examined. Although the magnetic structures correspond dominantly to a lattice of magnetic dipoles, the symmetry breaking to ferrimagnetic structures in a finite field is mediated by the coupling to a homogenous quadrupole (alignment), not possible in a spin-1/2 system. Our study provides a basis for further exploration of instabilities in driven multilevel systems with feedback.

Fabrication of nanostructures with complex spatial frequency via laser-focused atomic deposition

In this paper we report on experiments generating complex one-dimensional nanoscale patterns with the laser-focused atomic deposition technique. A beam of collimated chromium atoms intersect with an exact on-resonant laser standing wave at 7S3 → 7 transition of 52Cr. With the usage of proper laser intensity and reflectivity of the retroreflecting mirror, which are used to form the standing wave, nanolines with complex spatial frequencies (both λ/2 and λ/4) can be fabricated in one-step deposition. The proportion of the two structures could be 1:1.

Influence of Raman laser sidebands effect on the measurement accuracy of cold atom gravimeter

The technology of electro-optic modulation is one of the several methods of generating the Raman beams. The experimental system based on this method is simple and much easier to implement, and the environmental adaptability is strong as well. However, this kind of modulation technology will produce additional laser lines, which may affect the measurement accuracy of cold atom gravimeter. Based on a homemade transportable cold atom gravimeter, the influence of Raman sideband effect on the accuracy of cold atom gravimeter is investigated in this paper. We analyze in detail the relationship between Raman sideband effect and some experimental parameters, such as the height of Raman retro-reflection mirror, the time of free fall of the atoms, the detuning of Raman laser, etc. It is found that those parameters have a dominant influence on the measured gravity resulting from Raman sideband effect. Besides, it is also found that the gravity measurements will be sensitive again to some experimental parameters in the case of Raman sideband effect while these parameters are usually insensitive in case of laser system without sideband effect. Finally, we investigate the relationship between Raman sideband effect and Raman detuning, and presente a method of evaluating the gravity induced by Raman sideband effect. The experimental results in this paper can provide a reference for reducing the influence of Raman sideband effect on the accuracy evaluation of cold atomic gravimeter.

Spontaneous light-mediated magnetism in cold atoms

Cold atom setups are now commonly employed in simulations of condensed matter phenomena. We present an approach to induce strong magnetic interactions between atoms on a self-organized lattice using diffraction of light. Diffractive propagation of structured light fields leads to an exchange between phase and amplitude modulated planes which can be used to couple atomic degrees of freedom via optical pumping nonlinearities. In the experiment a cold cloud of Rb atoms placed near a retro-reflecting mirror is driven by a detuned pump laser. We demonstrate spontaneous magnetic ordering in the Zeeman sublevels of the atomic ground state: anti-ferromagnetic structures on a square lattice and ferrimagnetic structures on a hexagonal lattice in zero and a weak longitudinal magnetic field, respectively. The ordered state is destroyed by a transverse magnetic field via coherent dynamics. A connection to the transverse (quantum) Ising model is drawn.

Measurement of absolute gravity based on cold atom gravimeter at large tilt angle

The tilt angle of a cold atom gravimeter (CAG) could have a significant influence on the measurement of absolute gravity. The measurement, manipulation, and compensation of the tilt for CAG need to be conducted in order to obtain a high-accuracy absolute gravity measurement. In this paper, firstly, the influences of tilt on absolute gravity measurement under four different conditions are analyzed theoretically by taking into account the position of vacuum system relative to Raman retro-reflection mirror. Then, the experimental investigation is carried out and it is found that the measured results agree well with the theoretical prediction curves. According to the analysis above, we design a scheme for absolute gravity measurement based on two inclinometers, mainly to solve the problem of long-term tilt drift of CAG especially in harsh measurement environment. In this scheme, a high-resolution inclinometer is used to record the tilt angle of Raman retro-reflection mirror, which is fixed on a passive vibration isolation platform. Besides, another inclinometer is utilized to monitor the tilt angle of vacuum chamber of the CAG. By doing so, the vibration noise can be suppressed and the tilt data can be measured with a high precision. Finally, the experimental verification of this proposal is carried out based on our homemade compact cold atom gravimeter, and the high accuracy absolute gravity measurement is realized in a complex workshop environment. Since the vibration noise of Raman mirror is improved by using the vibration isolation platform, the sensitivity of our CAG can reach 319 μGal √Hz. Besides, we measure the long-term changes of gravity with time and find that the experimental results are consistent with the curves calculated by theoretical tidal model. Moreover, due to the precise measurement and compensation for the tilt drift, the accuracy of our CAG is estimated at 12.3 μGal. In order to evaluate this system accuracy, a comparison between our CAG and the FG5 at the same measured site is made. The absolute gravity values determined by both gravimeters coincide with each other. In this paper, we provide a feasible scheme for measuring the absolute gravity in the complex environment. The experimental demonstration of this measurement scheme is performed thereby acquiring some valuable reference data for the practical use of CAG.

Note: Laser frequency shifting by using two novel triple-pass acousto-optic modulator configurations

We report the design of two novel triple-pass acousto-optic modulator systems. These designs are extensions of the well known acousto-optic modulator (AOM) double-pass configuration, which eliminates the angle dependence of the diffracted beam with respect to the modulation frequency. In a triple-pass system, however, the frequency dependence of the angle does not disappear but the frequency shift is larger, spanning 3 times the AOM central frequency. In some applications, such as optically pumped Cesium-beam frequency standards, the frequencies of the two laser beams remain fixed and a triple-pass optical system can be used to reduce to one the number of lasers used in such atomic clocks. The two triple-pass configurations use either a retro-reflecting mirror, or a right angle prism to pass for third time the laser beam through the AOM, obtaining diffraction efficiencies of about 27% and 44%, respectively.

Development of JSNS target vessel diagnosis system using laser Doppler method

When an intense pulsed proton beam with a power of 1 MW is irradiated to a mercury target, a pressure wave caused by the proton beam gives a vibration on the target vessel. Pitting damage also occurs on the target vessel, especially incident beam area, resulting in shortening of a life-time. It is very important to monitor the vibration of the target vessel from the view point of the life-time estimation. We developed the target vessel diagnosis system using laser Doppler method and successfully installed it in an actual pulsed spallation source. The diagnosis system consists of retro-reflecting corner-cube mirror (reflective mirror) on the target, mirror assembly in a reflector plug and laser source-detector. The newly developed reflective mirror, made by nickel, was installed by vacuum silver brazing on the target vessel to detect the target vibration. In order to pass the laser beam to the target vessel, a mirror assembly was installed inside the reflector plug. It is replaceable using a remote handling machine during a maintenance period. Nd-YAG laser beam (wave length: 533 nm) with the power of 50 mW was adopted to detect the target vibration. The first proton beam to the target in the spallation neutron source (JSNS) was provided on 30 May 2008. The first signal related to the target vibration was also detected by using this target vessel diagnosis system.

Fourier Transform Near-Infrared Spectrometer Using a Corner-Cube Integrated Prism Scanning Interferometer

This paper describes a Fourier transform (FT) near-infrared spectrometer that uses an integrated prism scanning interferometer whose optical paths are stabilized by corner cubes. A combination of corner cubes and a retroreflection mirror, which is sometimes used in the conventional interferometer for FT spectrometers, is adopted and adapted to the integrated prism scanning interferometer through a special design. Without any degradation of spectroscopic properties, the optical path in the interferometer is highly stabilized and the moving distance of the stage is halved. These advantages provide a robust and portable FT spectrometer for field use.

Wave-mixing properties in commercially available semi-insulator grade GaAs crystals

We have been successful in procuring commercial semi-insulator grade GaAs crystals from Sumitomo that exhibit in our laboratory a gain coefficient of 6.4 cm(-1), a phase-conjugate beam reflectivity of 6, and a grating build-up time of less than 10 ms at a wavelength of 1.06 mum. Electrical and optical properties of these crystals in two- and four-wave-mixing experiments are described for both dc electric field and moving-grating biases on the crystal. Oscillator experiments have also been performed with a retromodulator as the retroreflective mirror in the feedback loop of the resonator cavity.