Showing papers in "Applied Physics B in 1992"
TL;DR: In this paper, an improved scheme to drive the stimulated Raman transitions was used to achieve a resolution of 3×10−8 g after 2×103 seconds of integration time.
Abstract: Velocity sensitive stimulated Raman transitions have been used to measure the gravitational acceleration, g, of laser cooled sodium atoms in an atomic fountain geometry. By using an improved scheme to drive the Raman transitions, we have demonstrated a resolution of 3×10−8 g after 2×103 seconds of integration time. In addition to presenting recent experimental results, we review the theory of stimulated Raman transitions as it applies to atom interferometers and discuss the prospects of an atom interferometer-based gravimeter with better than 10−10 g absolute accuracy.
426 citations
TL;DR: In this paper, a combined Raman elastic-backscatter lidar has been developed, where a XeCl excimer laser is used as the radiation source and inelastic Raman backscatter signals are spectrally separated from the elastic signal with a filter or grating polychromator.
Abstract: A combined Raman elastic-backscatter lidar has been developed. A XeCl excimer laser is used as the radiation source. Inelastic Raman backscatter signals are spectrally separated from the elastic signal with a filter or grating polychromator. Raman channels can be chosen to register signals from CO2, O2, N2, and H2O. Algorithms for the calculation of the water-vapor mixing ratio from the Raman signals and the particle extinction and backscatter coefficients from both elastic and inelastic backscatter signals are given. Nighttime measurements of the vertical humidity distribution up to the tropopause and of particle extinction, backscatter, and lidar ratio profiles in the boundary layer, in high-altitude water and ice clouds, and in the stratospheric aerosol layer are presented. Daytime boundary-layer measurements of moisture and particle extinction are made possible by the improved daylight suppression of the grating polychromator. Test measurements of the CO2 mixing ratio indicate the problems for the Raman lidar technique in monitoring other trace gases than water vapor.
415 citations
TL;DR: In this paper, the authors measured the excited singlet-state absorption cross section and the associated nonlinear refractive cross section using picosecond pulses at 532 nm in solutions of phthalocyanine and naphthalocaline dyes.
Abstract: Direct measurements are reported of the excited singlet-state absorption cross section and the associated nonlinear refractive cross section using picosecond pulses at 532 nm in solutions of phthalocyanine and naphthalocyanine dyes. By monitoring the transmittance and far-field spatial beam distortion for different pulsewidths in the picosecond regime, it is shown that both the nonlinear absorption and refraction are fluence (energy-per-unit-area) rather than irradiance dependent. Thus, excited-state absorption is the dominant nonlinear absorption process, and the observed nonlinear refraction is also due to real population excitation.
332 citations
TL;DR: In this paper, it was shown that in the presence of a DC electric field, the redistribution is not centrosymmetric and produces a poling of the film, and the evolution of the second-order nonlinear susceptibility, χ(2), was monitored by measuring the electro-optic effect by attenuated total reflection and by second-harmonic generation.
Abstract: The reversible cis-trans photoisomerization of disperse red 1 (DR1) in PMMA thin films has been demonstrated to be strongly polarization sensitive [1]. In this communication two mechanisms are identified: the angular hole burning and the angular redistribution of molecules. It is shown that, in the presence of a DC electric field, the redistribution is not centrosymmetric and produces a poling of the film. The evolution of the second-order nonlinear susceptibility, χ(2), is monitored by measuring the electro-optic effect by attenuated total reflection and by second-harmonic generation.
277 citations
TL;DR: In this article, a frequency tunable source of squeezed light has been developed which is suitable for a variety of spectroscopic applications, including frequency-modulated saturation spectroscopy in a vapor cell.
Abstract: A frequency tunable source of squeezed light has been developed which is suitable for a variety of spectroscopic applications. In initial experiments continuous tunability over a range of 2 GHz has been achieved with a directly observed nonclassical noise reduction of 6 dB relative to the vacuum-state limit in a balanced homodyne detector. A process of light-induced absorption in the nonlinear crystal has been identified as the principal loss mechanism which prevents the observation of yet larger degrees of squeezing. Although our source is potentially broadly tunable over the range of wavelengths from 840 to 970 nm, the current research centers on the performance at 852 nm for spectroscopy of the D
2 line of atomic cesium. For frequency-modulated (FM) saturation spectroscopy in a vapor cell, an improvement of 3.1 dB in sensitivity relative to the usual quantum limit is demonstrated for the detection of Doppler-free resonances. When corrected for the thermal noise of the detector, the enhancement in signal-to-noise ratio brought by the squeezed field is 3.8 dB relative to the shot-noise limit set by the vacuum fluctuations of the probe field.
151 citations
TL;DR: In this article, the EPR paradox is demonstrated experimentally for continuous variables by employing a nondegenerate optical parametric amplifier (NOPA), which is analogous to and under some ideal conditions is in one-to-one correspondence with the original system discussed by EPR.
Abstract: The Einstein-Podolsky-Rosen (EPR) paradox is demonstrated experimentally for continuous variables by employing a nondegenerate optical parametric amplifier (NOPA). Such a system is analogous to and under some ideal conditions is in one-to-one correspondence with the original system discussed by EPR. In particular, the quadrature-phase amplitudes for a signal beam are inferred in turn from those of a spatially separated but strongly correlated idler beam, where these optical amplitudes are analogous to canonical position and momentum variables. The variances for the two inferences are measured and their product is observed to be below the limit of unity associated with the Heisenberg uncertainty relation, in apparent contradiction with quantum mechanics according to the argument of EPR. The smallest product of inference variances achieved in the experiment is (0.70±0.01). Various other types of quantum noise for this system are also investigated, and a theory of a narrowband NOPA is presented with losses included. A comparison between experiment and this theory shows relatively good agreement. The question of a local hidden-variables description of the system is discussed.
129 citations
TL;DR: In this article, a new atomic cavity consisting of a single horizontal concave mirror placed in the earth's gravitational field is studied, where gravity, by bending the atomic trajectories, plays the role of a second mirror closing the cavity.
Abstract: This paper is devoted to the study of a new atomic cavity consisting of a single horizontal concave mirror placed in the earth gravitational field. Gravity, by bending the atomic trajectories, plays the role of a second mirror closing the cavity. We first discuss the stability criterion for this cavity, assuming that the mirror has a parabolic shape. We then derive the quantum mechanical modes of such a configuration, with particular emphasis on the paraxial (i.e., close to vertical) motion. Finally, we discuss the possibility of populating those modes from an initial cold atomic cloud dropped above the mirror.
108 citations
TL;DR: In this article, the Doppler shift of the backscattered echo is measured by intercomparing the signal detected through each of two narrow band-passes of a single dual Fabry-Perot interferometer tuned to either side of the emitted laser line.
Abstract: The possibility to measure winds in the middle atmosphere with a Doppler LIDAR was demonstrated in 1989. It has been used since then to study the wave-mean flow interaction, in association with the Rayleigh LIDAR providing density and temperature and their fluctuations. The Doppler LIDAR relies on Rayleigh scattering from air molecules and was originally designed to cover the height range 25–60 km, a region where radars cannot operate. The Doppler shift of the backscattered echo is measured by inter-comparing the signal detected through each of two narrow band-passes of a single dual Fabry-Perot interferometer tuned to either side of the emitted laser line. Its extension to lower altitudes where Mie scattering is present is under study.
101 citations
TL;DR: In this paper, the image amplitude and image spatial power spectral density produced by monochromatic point-source illumination of a finite (and/or infinite) periodic complex transmission grating were calculated.
Abstract: We present new methods and formulae for calculating the image amplitude and image spatial power spectral density produced by monochromatic point-source illumination of a finite (and/or infinite) periodic complex transmission grating. At specific finite-width resonances the image amplitude is seen to display periodic complex amplitude self-imaging of the grating, with interlaced alias images. The finite width grating resonances (as a function of spatial frequency) are broadened (from zero width) and displaced in frequency relative to those produced by an infinite grating, although the finite resonance width relative to illumination wavelength variation persists with infinite gratings. In the Fresnel domain the self images are generalizations of the Talbot and von Lau effects, while in the Fraunhofer to Fresnel transition domain, our formulae demonstrate the formation of these structures from Fraunhofer diffraction order side-lobes. Using these results, design criteria are provided for constructing lens-free three-grating interferometers with spatially diffuse illumination and detection. Such interferometers have a wide variety of applications for both X-rays and matter-waves, including a phase sensitive imaging device and/or narrow-band interference filter. For wavelengths in the Angstrom to sub-Angstrom range they feature high throughput and ease of fabrication. Experimental results using light with such an interferometer are presented. Our results conclusively demonstrate interference and image aliasing in such a device with spatially diffuse illumination and detection. The experiment is readily reproducible in any undergraduate physics laboratory.
80 citations
TL;DR: In this paper, the electrostrictional interaction of soliton pulses in optical fibers was studied and the effect of self-scattering of light on acoustic waves on the arrival time of optical pulses was considered.
Abstract: We present the theory of electrostrictional interaction of soliton pulses in optical fibers. Solitons excite acoustic waves propagating in the direction transverse to the fiber axis. Scattering of optical radiation on these waves leads to a timing jitter of the optical pulses arrival time. We consider this effect as nonlinear self-scattering of light on acoustic waves. Because of the fact that a value of acoustic lifetime can reach a value of about 100 ns self-scattering on acoustic waves can be observed for a single optical pulse as well as for an optical pulse sequence as a whole. The value of single soliton self-frequency shift due to excitation of acoustic waves as a function of soliton duration have been obtained. For soliton duration τsol > 14 ps an acoustic wave soliton self-frequency shift is larger than the Raman soliton self-frequency shift.
79 citations
TL;DR: In this article, it is shown that those atoms or molecules which happen to have positive Stark or Zeeman energy shift are repelled by regions of high electrostatic or magnetostatic energy density, respectively.
Abstract: Those atoms or molecules which happen to have positive Stark or Zeeman energy shift (by virtue of their particular internal quantum state) are repelled by regions of high electrostatic or magnetostatic energy density, respectively. Using electrostatic or magnetostatic fields, which are periodic in a plane, it is possible to construct mirrors and gratings for slowly moving atoms and molecules. The theory of such devices is presented, together with some ideas for their fabrication.
TL;DR: In this paper, the authors used an optical sensor combined with a Mach-Zehnder interferometric waveguide and optical fibers to measure slight changes of aqueous sugar concentrations.
Abstract: We used an optical sensor combined with a Mach-Zehnder interferometric waveguide and optical fibers to measure slight changes of aqueous sugar concentrations. The merits of this sensor are simplicity, reliability, high sensitivity and continuous monitoring. The technique is based on the fact that the refractive index of sugar solution changes with the concentration of sugar. In the experiment, one arm of the interferometer is clad with glue and is thus isolated from the sugar solution. The other one is exposed to the sugar solution. A single mode fiber is directly glued onto the interferometric waveguide, to guide the light into the interferometer. If the concentration of sugar covering the waveguide changes, the phase of propagating light in the exposed arm will be changed, while the phase in the other arm is fixed. Hence the output intensity from the interferometer is directly related to the concentration of the sugar solution. The result of this experiment yields the relation between the sugar concentration and output signal. From 0% to 1% concentration of sugar solution, there is only a 1.4×10−3 refractive index difference. Two sets of experimental data have been obtained, showing a linear relation between the sugar concentration and the output signal from our sensor. This sensor could be used for continuous monitoring of blood sugar in the human body.
TL;DR: In this article, it was shown that it is impossible to trap ground state particles at rest using arbitrary combinations of electric, magnetic, and gravitational fields, a result which is a considerable generalization of Wing's theorem.
Abstract: Possibilities of trapping ground state atoms in static fields are studied. It is shown that it is impossible to trap ground state particles at rest using arbitrary combinations of electric, magnetic, and gravitational fields, a result which is a considerable generalization of Wing's theorem. Similarly, it is impossible to make a thin lens for ground state atoms using static fields. Confinement of ground state particles in dynamic equilibrium can be achieved. Axially symmetric storage rings with electric or magnetic fields are possible and should be experimentally feasible. Such storage rings have the important advantage that ground state particles can be confined, hence loss of atoms by two-body collisions is avoided.
TL;DR: In this paper, a cylindrical lens potential was created by a large period (⋍ 45 μm) standing light wave perpendicular to a beam of metastable He atoms.
Abstract: A novel atomic lens scheme is reported. A cylindrical lens potential was created by a large period (⋍ 45 μm) standing light wave perpendicular to a beam of metastable He atoms. The lens aperture (25 μm) was centered in one antinode of the standing wave; the laser frequency was nearly resonant with the atomic transition 23S1−23P2 (λ=1.083 μm) and the interaction time was significantly shorter than the spontaneous lifetime (100 ns) of the excited state. The thickness of the lens was given by the laser beam waist (40 μm) in the direction of the atomic beam. Preliminary results are presented, where an atomic beam is focused down to a spot size of 4 μm. Also, a microfabricated grating with a period of 8 μm was imaged. We discuss the principle limitations of the spatial resolution of the lens given by spherical and chromatic aberrations as well as by diffraction. The fact that this lens is very thin offers new perspectives for deep focusing into the nm range.
TL;DR: In this paper, a multi-mode diode laser with an external cavity was studied experimentally and theoretically for its application to intra-cavity spectroscopy, and the authors proposed an adequate model for diode lasers based on rate equations and including frequency-dependent gain saturation.
Abstract: A multi-mode diode laser with an external cavity is studied experimentally and theoretically for its application to intra-cavity spectroscopy. One facet of a typical Ga0.89Al0.11As laser diode was antireflection-coated by deposition of HfO2 such that 10−3 residual reflectivity was left over. This diode was placed in an external optical cavity. The emission spectrum of this diode laser is highly sensitive to any frequency-dependent loss in the cavity, and the detectivity of such a loss grows with the pump rate. Even close to threshold, the absorption at 780 nm of Rb atoms with a density of 5×1010 cm−3 has been detected. An adequate model for diode lasers based on rate equations and including frequency-dependent gain saturation is developed and applied to the calculations of output spectra. The sensitivity of these spectra to intra-cavity absorption is determined by the overall cavity loss — which is rather high — and the fraction of spontaneous emission in the total emission, in contrast with dye lasers where it is limited by nonlinear mode coupling. Various criteria for the sensitivity are suggested. The smallest detectable absorption with a perfectly antireflection-coated laser is 10−6 cm−1. Improvement of the characteristics of the laser diode would increase the sensitivity.
TL;DR: In this article, a review of quantum non-demolition (QND) measurements in the optical domain can be found, which can be characterized using three criteria: the quality of the quantum measurement, the non-destruction of the signal, and the conditional variance of the output signal beam, given the output "meter" beam.
Abstract: We review the schemes which have been implemented, in order to achieve quantum non-demolition (QND) measurements in the optical domain. The simplest schemes can be obtained using the optical Kerr effect, which yields a crossed-phase modulation coupling between two light beams. Other schemes use either independently generated squeezed light, or coupled-mode parametric amplifiers. These various schemes can be characterized using three criteria, which describe, respectively, the quality of the quantum measurement, the non-destruction of the signal, and the conditional variance of the output signal beam, given the output “meter” beam (quantum-state preparation criterion). We show that quantitative limits can be defined with respect to these criteria, delimiting “classical” and “quantum” domains of operation. Then we present in more detail a new experimental implementation of QND measurements, using three-level atoms inside a doubly-resonant optical cavity.
TL;DR: In this article, it was shown that an atom interferometer based on the coherent splitting of the atomic wave function by four travelling waves (Ramsey interferometers) may be explained by a purely mechanical interpretation.
Abstract: In this paper it will be shown that an atom interferometer, based on the coherent splitting of the atomic wavefunction by four travelling waves (Ramsey interferometer), may be explained by a purely mechanical interpretation. As our first application of this Ramsey interferometer we have measured the phase shifts respectively optical length changes in a magnesium atomic beam caused by the acceleration of the partial atomic wave in one arm of the interferometer. This acceleration was achieved by the dipole force exerted by an off-resonant crossing laser beam which interacted with the ground state part of the wavefunction only. Further applications of this interferometer and improvements due to laser cooling will be discussed.
TL;DR: In this paper, two methods are described to monitor the temperature of the atmosphere from the ground to 100 km altitude, using the rotational Raman lines of O2 and N2.
Abstract: Two methods are described to monitor the temperature of the atmosphere from the ground to 100 km altitude The Rayleigh LIDAR is now widely used (the French network includes four of those characteristics of which are given), and here, the major results obtained from this technique are presented The second method, which completes the Rayleigh LIDAR downwards, uses the rotational Raman lines of O2 and N2 The method is briefly described and first results are presented Including both the Rayleigh and Raman modes leads to a continuous temperature measuring method to survey changes in the lower and middle atmosphere
TL;DR: In this paper, atom optics and interferometry based on laser manipulation of atoms and a use of microfabricated structures are reviewed, and a review of the use of interferometers is presented.
Abstract: Atom optics and interferometry based on laser manipulation of atoms and a use of microfabricated structures are reviewed.
TL;DR: In this article, it is demonstrated that one can measure the distribution of the transverse position of an atom crossing one or more optical cavities by monitoring the phase of the standing wave fields in the cavities.
Abstract: It is demonstrated that one can measure the distribution of the transverse position of an atom crossing one or more optical cavities by monitoring the phase of the standing wave fields in the cavities. For the atom-field interaction the Kapitza-Dirac regime is assumed; it is shown that in this regime the method represents a quantum nondemolition measurement of the atomic position. On the other hand it can be applied to prepare narrow distributions of the transverse atomic position. In order to show this, a numerical simulation is performed, which illustrates the collapse of a broad initial Gaussian wavepacket, which can be coherent or incoherent, to a distribution with narrow peaks. Preparing the cavity fields in a squeezed state, one can greatly enhance the impact of the cavity field measurements on the atomic density matrix.
TL;DR: In this article, the spatial distribution of electron density in argon microplasmas produced by laser ablation of solids has been investigated by time-resolved emission spectroscopy.
Abstract: The spatial distribution of electron density in argon microplasmas produced by laser ablation of solids has been investigated by time-resolved emission spectroscopy. The electron density was derived from Stark broadening and shift of spectral lines. It was found that the radial gradient of the electron density is much smaller than the gradient of the atomic number density of atoms ablated by the laser into the plasma. The almost homogeneous plasma conditions in the centre of the microplasmas are essential for quantitative element analysis of solid samples by laser ablation. On the other hand, because of the homogeneous conditions microplasmas are excellent sources for measurements of reliable Stark broadening and shift parameters of atomic and ionic spectral lines of all elements which can be ablated by lasers from solid samples.
TL;DR: In this article, the authors measured supersonic velocities up to a few hundred microns away from the irradiated surface, indicating the formation of shock waves and calculated the corresponding pressure.
Abstract: We investigate shock waves generated by excimer laser ablation of sheet polyimide confined in water. The velocities of the ablation-induced pressure waves in the water are determined by an optical probe system. We measure supersonic velocities up to a few hundred microns away from the irradiated surface, indicating the formation of shock waves. We use these velocities to calculate the corresponding pressures. They are already in the kbar range at fluences comparable to the threshold of ablation. The shock pressure varies as the square root of the incident laser fluence, a behavior that is explained by the rapid heating of the confined gaseous products of ablation. The initially planar shock waves propagate, become spherical, and decay within a few hundred microns in the surrounding water to acoustic waves. During spherical expansion the shock pressure drops as the inverse of the square of the propagation distance. The shock waves generated may be relevant in explaining photoacoustic damage observed in biological tissue after excimer-ablation at corresponding irradiances. They may also be important in material processing applications of excimer laser ablation of polymers as they can lead to plastic deformation.
TL;DR: In this article, the effect of a short prepulse on soft X-ray spectra from a plasma generated by a high intensity KrF* laser pulse (main pulse: 0.5 ps, intensity I�士main=5.3×1015 W/cm2) on flat targets of Al and Cu has been studied in detail.
Abstract: The effect of a short prepulse (0.5 ps) on soft X-ray spectra from a plasma generated by a high intensity KrF* laser pulse (main pulse: 0.5 ps, intensity I
main=5.3×1015 W/cm2) on flat targets of Al and Cu has been studied in detail. The spectra have been measured as a function of the pulse separation Δt between the two pulses and the prepulse intensity I
pre. It was found that both the overall emission and the line emission increased with Δt (at constant I
pre) and with I
pre (at constant Δt). In particular, lines in the shorter wavelength region had higher intensity. The influence of the prepulse on the line emission of specific transitions in the Al spectra was investigated systematicly. An explanation for the observed effects is given.
TL;DR: In this paper, the second-harmonic mode generated in a MgO:LiNbO3 external monolithic cavity pumped by a Nd:YAG laser was measured.
Abstract: We have measured the intensity fluctuations of the second-harmonic mode generated in a MgO:LiNbO3 external monolithic cavity pumped by a Nd:YAG laser. The cavity has mirror coatings for both the fundamental and the second-harmonic mode. We scan the cavity using the electro-optic effect of the crystal and observe that the second-harmonic beam of 2 mW exhibits a quantum noise reduction of 40(±5)%. In addition, we report on the active frequency stabilization of the monolithic device used in our squeezing experiments. Several fast tuning parameters such as the electro-optic effect, the photo-elastic effect, and the laser frequency have been investigated. With these tuning parameters the monolithic resonator can be locked on double-resonance at the phase-matching temperature, which is a prerequisit for observing squeezing in a cw-regime.
TL;DR: In this article, the atomic scattering from a standing-wave light beam in the Bragg regime was investigated, where momentum conservation requires the scattering to flip between two allowed directions only.
Abstract: We investigate the atomic scattering from a standing-wave light beam in the Bragg regime. Here momentum conservation requires the scattering to flip between two allowed directions only. In this limit an adiabatic approximation allows us to obtain analytic expressions for the flipping. The various orders of such resonances are compared with the multiphoton resonances observed in radio-frequency spectra, when they are interpreted in terms of Dopplerons. In addition to the main frequency of flipping, we find a modulation of the whole beam, which is seen when the scattered beam interferes with some differently prepared component of itself. We integrate the coupled equations numerically and find that the adiabatic approximation gives a good description of the processes over a large range of parameter values.
TL;DR: In this article, the first measurements of toluene by differential-absorption LIDAR in the near-ultraviolet spectral region were reported, generated by frequency doubling the output from a tunable dye laser in beta-barium borate.
Abstract: The first measurements of toluene by differential-absorption LIDAR in the near-ultraviolet spectral region are reported. A pulse energy of 4.5 mJ was used for the measurement, generated by frequency-doubling the output from a tunable dye laser in beta-barium borate. The magnitude of spectral interference from other pollutant species has been calculated and the extension of the system to measure other aromatic hydrocarbons in the same spectral region is discussed.
TL;DR: In this paper, the superradiant emissions at peak power as high as 7MW were measured at around 535 nm when the silica samples were excited by a XeF laser.
Abstract: Fluorescence and lasing properties of coumarindoped silica samples prepared by sol-gel process were investigated. Superradiant emissions at peak power as high as 7MW were measured at around 535 nm when the silica samples were excited by a XeF laser. The energy of the superradiant pulse was 89 mJ, corresponding to a conversion efficiency of 36.6%.
TL;DR: In this paper, the advantages and drawbacks of different nonlinear χ(3) materials for the purpose of generating squeezed light are discussed and the respective roles of nonlinearity, losses, response time and excess noise are discussed.
Abstract: We assess in this paper the advantages and drawbacks of different nonlinear χ(3) materials for the purpose of generating squeezed light. The respective roles of nonlinearity, losses, response time and excess noise are discussed. Two simple models of nonlinear media are considered more precisely: parametric media with linear losses and an empty cavity with moving mirrors.
TL;DR: In this paper, an interferometer in which an atom traverses two identical micromaser cavities in succession is proposed, and the probability for finding the atom in a definite final state displays Ramsey fringes or not.
Abstract: An interferometer in which an atom traverses two identical micromaser cavities in succession is proposed. Depending on the preparation of the cavity fields, the probability for finding the atom in a definite final state displays Ramsey fringes or not. If the initial cavity fields are such that the state of the atom between the cavities can be determined, then the Ramsey fringes disappear, as is required by the principle of complementarity.