Showing papers on "Astronomical interferometer published in 1991"
TL;DR: An atomic interferometers based on a Young's-type double-slit arrangement has been demonstrated and the good visibility of the observed fringes should make it possible to measure differential phase shifts in the interferometer of 1/3 rad in less than 10 min.
Abstract: An atomic interferometer based on a Young's-type double-slit arrangement has been demonstrated. A supersonic beam of metastable helium atoms passes through a 2-\ensuremath{\mu}m-wide slit in a thin gold foil. This transversely coherent beam impinges on a second microfabricated transmission structure, consisting of two 1-\ensuremath{\mu}m-wide slits at a lateral distance of 8 \ensuremath{\mu}m. This double slit defines two possible paths on which the atoms can reach the detector slit. The good visibility of the observed fringes should make it possible to measure differential phase shifts in the interferometer of 1/3 rad in less than 10 min.
510 citations
TL;DR: A calcium atomic beam excited in an optical Ramsey geometry was rotated about an axis perpendicular to the plane defined by the laser beams and the atomic beam and a frequency shift of the Ramsey fringes of several kHz has been measured.
Abstract: A calcium atomic beam excited in an optical Ramsey geometry was rotated about an axis perpendicular to the plane defined by the laser beams and the atomic beam. A frequency shift of the Ramsey fringes of several kHz has been measured which is proportional to the rotation frequency of the apparatus and to the distance between the laser beams. The results can be interpreted in three equivalent ways as the Sagnac effect in a calcium-atomic-beam interferometer: in the rotating frame of the laser beams either along straight paths or along the curved trajectories of the atoms, or in the inertial atomic frame.
436 citations
TL;DR: In this article, a three-grating geometry is used, in which the interfering beams are distinctly separated in both position and momentum, and the interference signal is 70 counts/s, which allows us to determine the phase to 0.1 rad in 1 min.
Abstract: We have demonstrated an interferometer for atoms. A three-grating geometry is used, in which the interfering beams are distinctly separated in both position and momentum. We used a highly collimated beam of sodium atoms with a de Broglie wavelength of 16 pm and high-quality 0.4-\ensuremath{\mu}m-period free-standing gratings which we fabricated using a novel method. The interference signal is 70 counts/s, which allows us to determine the phase to 0.1 rad in 1 min. Applications of atom interferometers are briefly discussed.
404 citations
TL;DR: In this paper, an interferometric fiber-optic sensor using a light-emitting diode (LED) as the optical source is analyzed and demonstrated using two Fabry-Perot interferometers (FPIs) in series, one for sensing and one which serves as a reference.
Abstract: An interferometric fiber-optic sensor using a light-emitting diode (LED) as the optical source is analyzed and demonstrated. The sensor arrangement employs two Fabry-Perot interferometers (FPIs) in series, one for sensing and one which serves as a reference. The optical output from the LED is spectrally modulated by reflection from the sensing FPI. Then, reflection or transmission by the reference FPI produces an interferometric beat response similar to that observed when a laser is used with the sensing interferometer alone. Best fringe visibility is obtained when the optical path lengths of the two interferometers are matched, and the fringes disappear when the path length difference becomes substantially greater than the coherence length of the LED. >
176 citations
TL;DR: Sensitive interferometry is proposed and demonstrated that permits the separation of the real and imaginary parts of the nonlinear susceptibility with a femtosecond time resolution by a single measurement.
Abstract: We propose and demonstrate sensitive interferometry that permits the separation of the real and imaginary parts of the nonlinear susceptibility with a femtosecond time resolution by a single measurement. A special reference interferometer compensates for any fluctuations of the fringe and provides high sensitivity to detect a fringe shift as small as 0.025 rad (lambda/250) by averaging only 100 shots with a low-repetition-rate laser. This method can be applied to materials with optical anisotropy and/or absorption with high sensitivity. We apply the method to two materials, CS(2) and CdS(x)Se(1-x) microcrystallite-doped glass.
150 citations
TL;DR: Ultrafast highly stable all-optical logic operations, including inversion, AND, Xor, and XOR, in a two-wavelength nonlinear Sagnac interferometer with two control beams have been reported.
Abstract: Ultrafast highly stable all-optical logic operations, including inversion, and, xor, and XOR¯, in a two-wavelength nonlinear Sagnac interferometer with two control beams have been reported. The interferometer consists of a dichroic polarization-maintaining fiber coupler and a 200-m-long dispersion-shifted polarization-maintaining fiber Sagnac loop. The logic operations were successfully demonstrated at multigigabit operation per second, and the required signal power was 1.8 W for a 200-m fiber.
114 citations
TL;DR: In this article, the optical amplification in a nonlinear fiber interferometer based on degenerate four-wave mixing (DFWM) was observed and the results were in agreement with a classical derivation for the nonlinear phase shift and gain.
Abstract: A report is made on the observation of optical amplification in a nonlinear fibre interferometer, based on degenerate four-wave mixing (DFWM). The results are in agreement with a classical derivation for the nonlinear phase shift and gain.
106 citations
TL;DR: This two-photon interference experiment in a Michelson interferometer with photon pairs produced by spontaneous parametric down-conversion shows the nonclassical nature of the observed interference and should allow further spinfree tests of Bell's inequalities.
Abstract: We perform a two-photon interference experiment in a Michelson interferometer with photon pairs produced by spontaneous parametric down-conversion. The interferometer is set to a path difference much larger than the coherence length of the light field. Application of a time-resolved coincidence detection scheme reveals two-photon interference fringes with a visibility of 87%. This high visibility clearly demonstrates the nonclassical nature of the observed interference and should allow further spin-free tests of Bell's inequalities.
95 citations
Journal Article•
TL;DR: In this article, the authors proposed a new technique, the squeezed-state technique, that allows one to decrease the photon-counting error while increasing the radiation pressure error, or vice versa.
Abstract: The interferometers now being developed to detect gravitational waves work by measuring the relative positions of widely separated masses. Two fundamental sources of quantum-mechanical noise determine the sensitivity of such an interferometer: (i) fluctuations in number of output photons (photon-counting error) and (ii) fluctuations in radiation pressure on the masses (radiation-pressure error). Because of the low power of available continuous-wave lasers, the sensitivity of currently planned interferometers will be limited by photon-counting error. This paper presents an analysis of the two types of quantum-mechanical noise, and it proposes a new technique---the "squeezed-state" technique---that allows one to decrease the photon-counting error while increasing the radiation-pressure error, or vice versa. The key requirement of the squeezed-state technique is that the state of the light entering the interferometer's normally unused input port must be not the vacuum, as in a standard interferometer, but rather a "squeezed state"---a state whose uncertainties in the two quadrature phases are unequal. Squeezed states can be generated by a variety of nonlinear optical processes, including degenerate parametric amplification.
95 citations
TL;DR: In this paper, the authors describe a new method for determination of the total phase difference of light waves without interference fringe counting, in which the displacements are determined only by the final values of intensity regardless of the velocity and any prior displacements.
89 citations
TL;DR: In this article, the theoretical performance limits of stationary Fourier spectrometers without mechanical scanning are analyzed and compared with the performance of a scanning Fourier Spectrometer employing uncollimated light are most favorable.
Abstract: Theoretical performance limits of stationary Fourier spectrometers without mechanical scanning are analyzed and compared with the performance of a scanning Fourier spectrometer. Spectrometers employing uncollimated light are most favorable. In amplitude-splitting interferometers the reduction in fringe visibility brought about by the extended source can be avoided and leads to high optical throughput in the corresponding spectrometer. In a stationary wave-front-splittirig interferometer, realized without a beam splitter, the fringe contrast depends on the size of the source. The use of a slit source increases the optical throughput of source-size-limited spectrometers.
TL;DR: In this paper, the authors derive upper limits on the optical wavelength uncertainty and express them as a function of optical path difference between the object and reference beams, phase measurement errors, and the synthetic wavelength.
Abstract: The phase ambiguity in conventional interferometers can be removed by using two laser diodes of different optical frequencies to generate a synthetic wavelength. However, the stability requirements for a two-color interferometric laser gauge that must provide unambiguous determination of the optical fringe order over a large distance can be severe. We derive upper limits on the optical wavelength uncertainty and express them as a function of optical path difference between the object and reference beams, phase measurement errors, and the synthetic wavelength. A simple stabilization arrangement is proposed, involving simultaneous servo control of both lasers with a single Fabry-Perot etalon. The experimental implementation of the proposed system demonstrates its effectiveness for long-term (16-h) stabilized two-color interferometry over a distance of 250 mm, with a 15-mm synthetic wavelength and a repeatability of 40 nm. For periods of < 1000 s, the repeatability was 8 nm.
TL;DR: Frequency dependences of main parameters of the interferometer are obtained and the possibility of high precision measurements of velocity and absorption of ultrasound in liquids under the high pressures by means of fixed path interferometers with liquid-backed transducers is shown.
TL;DR: FIFI as mentioned in this paper is an imaging spectrometer with two or three Fabry-Perot interferometers in a series for astronomical observations in the FIR range, which can be obtained with 2 km/s resolution.
Abstract: FIFI, an imaging spectrometer with two or three Fabry-Perot interferometers in a series for astronomical observations in the FIR range, is described. Spectral resolutions of 2 km/s can be obtained with FIFI. Design considerations are discussed as well as optics, the detector array, the transimpedance amplifier array, signal demodulation, data acquisition, and instrument control.
TL;DR: In this paper, a guided-wave Mach-Zehnder interferometer structure, based on the use of a four-port hybrid optical coupler consisting of symmetric and nonsymmetric y junctions, is proposed for wavelength division multiplexing application.
Abstract: A guided-wave Mach-Zehnder interferometer structure, based on the use of a four-port hybrid optical coupler consisting of symmetric and nonsymmetric y junctions, is proposed for wavelength-division multiplexing application. This structure provides less sensitivity to fabrication parameters and optical polarization, and can also be applied to a wide-wavelength spacing operation. Interferometers for wavelength splitting in the 1.3- and 1.55- mu m windows were designed and fabricated into a glass substrate with a dry silver ion exchange process. The measured crosstalk was -30 dB with nonpolarized light. >
TL;DR: A method for the measurement of fast, intensity-dependent refractive-index changes with the use of a modified Sagnac ring interferometer is presented and it is shown that the measurement is not degraded by slowly responding background index changes.
Abstract: A method for the measurement of fast, intensity-dependent refractive-index changes with the use of a modified Sagnac ring interferometer is presented. The measurement is not degraded by slowly responding background index changes. Nonlinear refractive-index changes in an undoped silicon wafer, and in poly-bis toluene sulfonate polydiacetylene and dye-doped polymethyl methacrylate waveguides, were measured with the use of a cw mode-locked Nd:YAG laser.
TL;DR: A stabilized fiber-optic interferometer was developed for vibration measurement by using two laser diodes of different wavelengths and one polarization-maintaining fiber to obtain the vibration amplitude.
Abstract: A stabilized fiber-optic interferometer was developed for vibration measurement by using two laser diodes of different wavelengths and one polarization-maintaining fiber. Passive signal processing of two signals in quadrature is used to obtain the vibration amplitude with a resolution of approximately 0.1 nm. An extension of the signalprocessing scheme is proposed that provides compensation for bending or temperature-induced transmission losses of the two propagation modes of the fiber.
TL;DR: A modified signal-processing technique that overcomes the limitations of the J(1) ...
Abstract: Fiber-optic interferometers have been studied extensively for sensing applications. Recently a technique described as the J1 … J4 technique was reported for the linear measurement of dynamic phase changes in a fiber interferometer that requires no phase bias and for which the measurement is independent of random phase fluctuations. However, the implementation of the J1 … J4 technique is limited because only the magnitude of the J1 … J4 Bessel components can be measured on a spectrum analyzer without information available on the sign of the Bessel function. Here a modified signal-processing technique that overcomes the limitations mentioned above is described.
TL;DR: In this article, a simple optic fiber displacement sensor for a scanning force microscope (SFM) is presented, which minimizes the alignment difficulties after a cantilever is changed and is easily adaptable to tube scanners so very compact SFM designs should be possible for imaging at low temperatures or in strong magnetic fields.
Abstract: We present a simple optic‐fiber displacement sensor for a scanning force microscope (SFM) The design minimizes the alignment difficulties after a cantilever is changed and is easily adaptable to tube scanners so very compact SFM designs should be possible for imaging at low temperatures or in strong magnetic fields We also provide a theoretical analysis and results to show that the sensitivity of the device can be improved by increasing the reflectivity of the fiber end The increased sensitivity makes it possible to work under fluids
TL;DR: A particular application to fringes of equal chromatic order can be utilized to obtain precise measurements of the thickness of extremely thin films sandwiched between two substrates.
Abstract: We present a simple analytic solution for the condition of constructive interference for light transmitted through an interferometer incorporating three ideally transparent layers of arbitrary thickness and refractive index. We also consider the effect of adding two metallic coatings to the outer surfaces of the interferometer and give empirical expressions for the associated phase changes for silver coatings on silica, sapphire, and mica substrates. A particular application to fringes of equal chromatic order can be utilized to obtain precise measurements of the thickness of extremely thin films sandwiched between two substrates.
TL;DR: All-optical switching is demonstrated in a 200-m-long fiber nonlinear Mach-Zehnder interferometer and stable operation is obtained by using a twin-core fiber.
Abstract: All-optical switching is demonstrated in a 200-m-long fiber nonlinear Mach–Zehnder interferometer. The only stabilization mechanism used is passive enclosure of the interferometer. Stable operation is obtained by using a twin-core fiber. The experiment demonstrates the feasibility of use of fiber nonlinear Mach–Zehnder interferometers for ultrafast switching and pipeline logic.
01 Jan 1991
TL;DR: In this paper, a new Zeiss interferometer, the Direct 100, is described, which is applicable to measurements in the presence of vibrations, measurements requiring the highest spatial resolution, integration of testing into manufacturing, use of interferometry for optimum assembly of complex systems, highprecision measurements in air with sub-nm accuracies, absolute calibration of residual errors, testing of aspheres with partial compensation and electronic hologram, measurement of fast processes, and temporally resolved measurements.
Abstract: A new Zeiss interferometer, the Direct 100, is described. This interferometer contains important improvements that are especially applicable to measurements in the presence of vibrations, measurements requiring the highest spatial resolution, integration of testing into manufacturing, use of interferometry for optimum assembly of complex systems, high-precision measurements in air with sub-nm accuracies, absolute calibration of residual errors, testing of aspheres with partial compensation and electronic hologram, measurement of fast processes, and temporally resolved measurements. The measurement and evaluation principle of the Direct 100 are described along with its optics, mechanics, and electronics.
TL;DR: The small value found for the outer scale of turbulence implies a narrow range of validity for application of Kolmogorov's law to calculate the atmospheric limitations to the performance of telescopes and interferometers.
Abstract: The small value found for the outer scale of turbulence (namely, ≤5 m) implies a narrow range of validity for application of Kolmogorov’s law to calculate the atmospheric limitations to the performance of telescopes and interferometers. Optical and radio seeing measurements are analyzed in support of a proposed turbulence spectrum which exhibits a spectral gap for scales (and hence interferometer baselines) between ∼10 and 1500 m but which obeys a 5/3 power law between 1500 and 20,000 m. The implications for forecasting the performance of optical and radio telescopes and interferometers are important.
Patent•
28 May 1991
TL;DR: In this paper, an extended interferometer having a plurality of sensors and a compensating interferometers is used to reduce and prevent polarization fading in unbalanced measuring interferometry.
Abstract: Apparatus and methods for reducing and preventing polarization fading in unbalanced measuring interferometers. An extended interferometer having a plurality of sensors and a compensating interferometer are used. They are driven from a pulsed optical signal source wherein the optical signal comprises sequences of two pulses each. To prevent polarization fading the polarization of a predetermined one of each two-pulse sequence is switched, preferably orthogonally, from sequence to sequence. Interference pulse output groups are produced for each two-pulse driving sequence. Each output group has the same number of usable pulses as the number of sensors in the interferometer.
TL;DR: In this paper, the probability density function (PDF) of the fluctuating output intensity of a two-beam interferometer, illuminated by a semiconductor laser, is described theoretically and experimentally.
Abstract: The probability-density function (PDF) of the fluctuating output intensity of a two-beam interferometer, illuminated by a semiconductor laser, is described theoretically and experimentally. The PDF, while dominated by the laser phase noise, may be substantially modified both by the laser intensity noise and by the thermal noise and bandwidth limitations imposed by the detection system. Two regimes of operation are explored. In the coherent regime, for which the interferometer ’ s differential delay τ is much smaller than the laser coherence time τc, the form of the PDF is highly sensitive to the mean phase difference between the interfering beams: The PDF is strongly asymmetrical for mean phase differences of 0 and π (experimentally reported here for the first time to our knowledge) but is symmetrical when the interferometer is in quadrature. In the incoherent regime, for which τ ≫ τc, the PDF is insensitive to such phase differences. The experimental results are in excellent agreement with a numerical simulation for which it is assumed that the laser phase noise is a Wiener process and for which the finite bandwidth of the detection system, as well as the effects of laser intensity noise and system thermal noise, is taken into account.
Patent•
07 Jun 1991
TL;DR: In this article, a reference laser is provided and directed through the optical train to the wafer which partially reflects the reference beam back to an interferometer, with interference fringes being detected by the full aperture sensor.
Abstract: The in situ process control system includes a full aperture sensor for observing the wafer through the optical train. A reference laser is provided and directed through the optical train to the wafer which partially reflects the reference beam back to an interferometer, with interference fringes being detected by the full aperture sensor. The interferometer provides a map of optical path difference before and during exposure which is then used by the control processor to monitor and control wafer warpage, aberration and distortions due to thermal effects and prior process steps. The reference laser may have multiple wavelengths to differentiate between the photoresist and the underlying layer on the wafer. Backscattered light from the wafer back through the optical train and the mask or mask plane is used to monitor exposure realtime. This monitor collects data on the actual delivered irradiance and stores it in the control processor, the data being used to determine resist characteristics, focus characterization, pattern definition, registration and alignment. The control processor receives information from the interferometers and other sensors and, using a library of algorithms, adapts the stepper to the desired characteristics by causing changes in focus, mask manipulation, wafer chuck manipulation, etc.
TL;DR: The sensing of temperature and of ultrasonic pressure with fiber-optic Fabry-Perot interferometers embedded in aluminum is demonstrated and the optical phase in an embedded interferometer is found to be 2.9 times more sensitive to temperature change than for the sameinterferometer in air.
Abstract: The sensing of temperature and of ultrasonic pressure with fiber-optic Fabry–Perot interferometers embedded in aluminum is demonstrated. The metal parts are cast in air by using graphite molds. Breakage of the fibers at the air–metal interface during the casting process is avoided through the use of stainless-steel stress-relief tubes. The optical phase in an embedded interferometer is found to be 2.9 times more sensitive to temperature change than for the same interferometer in air, in good agreement with model calculations. An embedded interferometer has also been used to detect ultrasonic waves over the frequency range of 0.1–8 MHz.
TL;DR: In this article, an optical interferometric instrument for the measurement of distance and position is presented, which is based on a high-frequency sinusoidal phase modulation interferometer.
Abstract: An optical interferometric instrument for the measurement of distance and position is presented. The system is based on a high‐frequency sinusoidal phase‐modulation interferometer. Phase modulation of the laser beam in one of the two interferometer arms is obtained by means of an electro‐optic modulator operating at frequencies up to 10 MHz. The electronic unit performs synchronous demodulation of the signal coming from the photodetector. The resulting signals are fed to an up‐down counting logic that is interfaced to a personal computer. The performance of the instrument has been evaluated by means of a system calibration against a reference high‐precision commercial interferometer. The overall accuracy of the system resulted to be within 80 nm, at target speeds up to 1 m/s. In this article, the optical setup, the electronic equipment, and the calibration results are presented.
TL;DR: In this paper, the authors discuss the triple-correlation imaging in optical astronomy, including speckle masking, spectroscopy, and optical long-baseline interferometry with arrays of large telescopes.
Abstract: Publisher Summary This chapter discusses the triple-correlation imaging in optical astronomy. The chapter discusses the high-resolution imaging methods of speckle masking (bispectrum or triple correlation processing), speckle spectroscopy, and optical long-baseline interferometry with arrays of large telescopes. The speckle spectroscopy methods have the advantage that they yield the spectrum of each resolution element of the object in addition to the high-resolution image. The additional spectral information is important for the study of the physical nature of astronomical objects. The advantage of the optical long-baseline interferometry with three or more telescopes is that, it can yield images and spectra with excellent angular resolution. Speckle masking is useful in the multi-speckle case, in experiments at visible wavelengths, and with interferometers consisting of large telescopes, such as the very large telescope (VLT) of the European Southern Observatory.
TL;DR: In this paper, a 35 meter baseline orbiting optical interferometer is studied as a focus mission for a testbed for controlled structures research, which captures the essential architecture, physics and performance requirements of a full scale instrument.
Abstract: A class of proposed space-based astronomical missions requiring large baselines and precision alignment can benefit from the application of Controlled Structures Technology. One candidate mission, that of a 35 meter baseline orbiting optical interferometer, is studied as a focus mission for a testbed for controlled structures research. Interferometry science requirements are investigated and used to design a laboratory testbed which captures the essential architecture, physics and performance requirements of a full scale instrument. Testbed hardware used for identification and control is presented, including an on-board six-axis laser metrology system using state of the art cat's eye retroreflectors. The testbed and research program are discussed in terms of controlled structures design and in terms of the expected benefits to the optical engineering and science communities.