Frequency-stabilized He-Ne Laser Research Articles

Absolute distance measurement using frequency sweeping interferometry with large swept range and target drift compensation

Frequency sweeping interferometry (FSI) is an attractive absolute distance measurement (ADM) method because of the advantages of large unambiguity range, simple structure and excellent flexibility. By using a reference interferometer (RI), the calibration of the frequency sweeping range in FSI can be avoided, and the complexity and cost of the system can be further reduced. Then, the measurement accuracy is associated with the accuracy of phase demodulation, the range of frequency sweeping and the compensation of target drift. In this paper, ADM using FSI with large swept range and target drift compensation is presented. A frequency stabilized HeNe laser that travels along the same optical path with the swept source laser was employed to monitor the target drifts of the measurement interferometer and RI. Interference phases of the corresponding interferometers were extracted simultaneously using phase generated carrier demodulation technique, and an accuracy better than 1° was verified by nanometer displacement measurement. Comparative experiments of ADM at a distance of ∼4.5 m with different swept ranges before and after target drift compensation were carried out, and the results demonstrated that larger swept range and target drift compensation could greatly improve the stability and accuracy of measurement.

Iodine frequency-stabilized HeNe laser amplified by injection locking of a semiconductor laser diode

The realisation of the metre definition is still today mostly performed using iodine frequency-stabilized HeNe lasers. Unfortunately, they deliver little optical power. Instead of migrating to other expensive laser technologies, the use of an injection locked semiconductor laser is proposed in order to boost the optical output of the legacy HeNe laser primary reference. The characterisation of the system and its validation through a comparison measurement is reported whereby no impact on the frequency and the stability of the HeNe reference laser could be observed.

Picometer mechanical displacement measurement using heterodyne interferometer with phase-locked loop

In this paper, we show picometer-order mechnical displacmment measurements using a heterodyne interferometer with a phase-locked loop (PLL). A heterodyne light source for the interferometer is implemented with a frequency stabilized HeNe laser and two acousto-optic modulators. A real time phase measurement is performed by the PLL, whose software is programmed in a field-programmable gate array (FPGA). A stiff parallel spring stage combined with a high-voltage piezoelectric actuator is used to generate picometer-order mechanical motion. With the above implementations, mechanical displacement of 10 picometer or less can be measured.

Ultrastable offset-locked frequency-stabilized heterodyne laser source with water cooling.

An ultrastable frequency-stabilized He-Ne laser with a water-cooling structure has been developed for a high-speed and high-accuracy heterodyne interferometer. To achieve high frequency stability and reproducibility, a two-mode He-Ne laser was offset locked to an iodine-stabilized laser. An improved synchronous multi-cycle offset frequency-measurement method with a gate time of an integer multiple of the modulation period was employed to remove the frequency-modulation effect on the offset-frequency counter. A water-cooling structure based on the double-helix structure was established to provide a stable and low-temperature working environment. This structure can remarkably reduce the frequency instability arising from the environmental temperature variation and the thermal pollution released from the laser to the environment. The experimental results indicate that the frequency stability according to the Allen variance is better than 2.3×10-11 (τ=10 s) and the frequency reproducibility is better than 4.5×10-10.

Vacuum wavelength calibration of frequency-stabilized He-Ne lasers used in commercial laser interferometers

We report on the calibration results of the wavelength of the lasers used in commercial laser interferometers, including the vacuum wavelength deviation from its nominal value, the vacuum wavelength stability, the repeatability of stabilized wavelength, and the secular change of these properties, by analyzing the calibration data accumulated for more than two decades. We present an experimental method of calibrating the frequency of laser interferometers. We also propose a proper time interval and an appropriate uncertainty expression for the vacuum wavelength calibration of the laser interferometers.

Characterization of Fabry-Perot interferometers and multi-etalon transmission profiles

Aims. Properly characterizing Fabry-Perot interferometers (FPI) is essential for determining their effective properties and evaluating the performance of the astronomical instruments in which they are employed. Furthermore, in two-dimensional spectrographs where multiple FPI are used in series, the actual distribution of plate separation errors will be crucial for determining the resulting transmission profiles. We describe techniques that address these issues utilizing the FPI of IBIS, a solar bidimensional spectrometer installed at the Dunn Solar Telescope. Methods. A frequency-stabilized He-Ne laser was used in three different optical layouts to measure the spatially-resolved transmission of the FPI. Analyzing the shape and wavelength shift of the observed profiles allows the characteristics of the cavity errors and the interferometer coating to be determined. Results. We have measured the spatial distribution of the large-scale plate defects, which shows a steep radial trend, as well as the magnitude of the small-scale microroughness. We also extracted the effective reflectivity and absorption of the coating at the laser line wavelength for both interferometers. Conclusions. These techniques, which are generally applicable to any Fabry-Perot interferometer, provide the necessary information for calculating the overall instrumental profile for any illuminated area of the interferometer plates. Accurate knowledge of the spectral transmission profile is important, in particular when using inversion techniques or in comparing observations with simulated data.

An LGN-303 frequency-stabilized He-Ne laser with a modulating attachment

The operating principle and elements of the construction of an LGN-303 frequency-stabilized He-Ne laser with a modulating attachment are considered. The basic parameters of the laser are presented, and some recommendations are given concerning the use of a modulating attachment in He-Ne lasers stabilized with the aid of an iodine absorption cell.

음향광변조기를 이용한 고분해능의 헤테로다인 간섭식 열팽창 측정기술

열팽창계수의 정확한 측정은 재료과학이나 공업기술 분야에서 가장 중요한 요구량 중의 하나이다. 음향광변조기(AOM)를 이용한 고분해능 간섭식 열팽창계를 제작하여 성능검사를 하였다. 이 계는 이중광로 헤테로다인 간섭계와 복사열 전기로로 구성되어, 정밀한 변위의 측정과 시료의 신속한 가열 및 냉각이 가능토록 하였다. 또한 레이저의 주파수 안정화를 위하여 2차 맥놀이 주파수를 이용한 3종모드 안정화 He-Ne 레이저를 제작하였으며, 이때의 주파수 안정도는 5<TEX>$\times$</TEX><TEX>$10^{-9}$</TEX>이었다. 제작된 계의 길이 측정은 실온에서 1100k온도영역에서 나노미터 정도의 정밀도를 주었다. The accurate measurements of thermal expansion coefficients is one of the most important techniques required not only in material science but also in industries. A high precision interferometric dilatometer, using acoustic optical modulator, has been constructed and its performance has been tested. The system consists of a double-path optical heterodyne interferometer and a radiant heating furnace. This provides highly accurate length measurement, and allows rapid heating and cooling method for the specimen. A three longitudinal mode frequency stabilized He-Ne laser, using the secondary beat frequency, is constructed. Its stability is found to be <TEX>$5{\times}10^{-9}$</TEX>. The uncertainty in the length measurement is estimated to be of nanometer order in the range between room temperature to 1100 K.

STRONG HYPERFINE SPECTRA OF 127I2 AT 633nm AND FREQUENCY STABILIZED TUNABLE DIODE LASER

In this paper, five groups of stronger hyperfine transitions of iodine molecule (127I2) are reported, which are to our knowledge first observed by us. Frequency separations and relative intensities of each transition are calculated. The calculated results and the observed values match very well. With the calculated results, we assigned the vib-rotational bands of each transition. Because the intensities of the newly observed transitions are hundreds of times stronger than transition R(127)11-5, which is applied to frequency-stabilized He-Ne laser, we use them as reference lines of iodine frequency stabilized tunable diode laser and get an output laser 3mW. This kind of frequency-stabilized diode laser may become a new kind of frequency standard.

Common-path optical heterodyne profilometer: a configuration

A novel configuration that combines a linearly polarized He-Ne laser and a birefringent lens to produce a common-path polarized optical heterodyne profilometer with respect to the heterodyned P and S waves has been set up. In this profilometer a linear polarized frequency-stabilized He-Ne laser was used with an acousto-optical modulator to replace the Zeeman laser as the light source that had two polarization eigenstates in different temporal frequencies. The proposed interferometer shows a more symmetric and ideal common-path structure than the conventional optical heterodyne profilometers with the Zeeman laser. The phase error aroused by the elliptical polarization and the nonorthogonality of the two eigenpolarization modes of the Zeeman laser can be reduced. The system's resolution in the vertical direction reaches 2 A, and in a 27-mum scanning range the repeatability of the surface profile measurements is shown to be 5 A.

Frequency-stabilized He-Ne laser for WINDII interferometer calibration on board the UARS-NASA satellite

The Upper Atmosphere Research Satellite (UARS) is dedicated to the study of the earth's atmosphere, composition, and temperature. It carries several instruments. Among them, WINDII is a Michelson interferometer used to observe wind and temperature in the upper mesosphere and thermosphere. The onboard calibration of the interferometer requires a He-Ne laser of frequency stability of 10-9. To be used in the space environment, particular specifications have been met by a special design described here. Performances of the system are shown and analyzed.

Laser frequency stability measurement using a Fabry-Perot based system

Electronic circuitry utilising digital-to-analogue converters, in conjunction with a commercially available 300 MHz scanning Fabry-Perot (FP) interferometer, has been designed to monitor laser frequency variations between two laser modes of widely different wavelength (in this case a single mode HeNe laser operating at 543 nm (green) and a highly stable laser operating at 633 nm (red)). Measurements of the frequency variation of the green laser relative to the red laser have been performed over periods of several hours. The accuracy of the measurements has been measured at better than 1 MHz using two stabilised 633 nm HeNe lasers and excellent linearity has been achieved. Compensation circuitry to negate the effects of the observed thermal drift of the Fabry-Perot interferometer is also described. The addition of fairly standard laser heater control circuitry to the output of the measurement system enables stabilisation of any other laser to a 633 nm frequency stabilised HeNe laser (subject to the finesse of the FP cavity).

Volume Determination of Fused Quartz Spheres

The volume determination of fused quartz spheres used for the absolute measurement of the density of water is described. The diameters of the spheres are measured with an optical interferometer, in which the sphere is placed between two parallel étalon plates of accurately known separation, and the diameters are obtained by measuring the gaps between each étalon surface and the sphere. Two wavelengths, 633 nm of a frequency stabilized He-Ne laser and 441 nm of a He-Cd laser, are employed in order to use the method of exact fractions. Details are given of a special arrangement for the interferometer which overcomes the low reflectivity of the surface of the fused quartz. A method to eliminate the spurious effect due to the transparency of the quartz sphere is also described. The diameters (about 85 mm) have been measured with standard deviations of 5 to 12 nm, which correspond to 0.16 to 0.43 ppm in terms of the volume. The total uncertainties of the volume are estimated to be 0.26 to 0.48 ppm.

Frequency stabilisation of λ/4-shifted DFB laser to stabilised optical resonator

The frequency of a 1.55µm-range GaInAsP λ/4-shifted DFB laser is locked to the resonant frequencies of a confocal etalon of which the mirror spacing is stabilised with a frequency-stabilised HeNe laser. An Allan variance of less than 10-11 was achieved for averaging times longer than 1 s without frequency modulation of the laser diode.

100 Mbit/s PSK heterodyne experiment using a travelling-wave laser amplifier

A 100 Mbit/s PSK heterodyne coherent optical communication system has been demonstrated using a frequencystabilised HeNe laser transmitter. The experiment incorporated a travelling-wave laser optical amplifier which gave 8 dB fibre-to-fibre gain with no significant system penalty.

Preliminary experiment for optical heterodyne communication with a single-mode optical fiber by using frequency-stabilized He–Ne lasers

Frequency fluctuation in a single-mode optical fiber is briefly discussed, and a preliminary experiment for optical heterodyne communication in a single-mode fiber is carried out with the aid of frequency-stabilized He-Ne lasers operating at a wavelength of 0.633 microm. As a result, we have obtained clear demodulated signals, having sinusoidal, triangular, and rectangular waveforms, through an optical fiber 100 m in length.

A method for stabilising an air-spaced Fabry-Perot etalon

A simple method is described for stabilising the optical thickness of the air gap in a piezoelectric Fabry-Perot etalon. The spacing between the plates is controlled by an error signal proportional to the difference in intensity of two orthogonally polarised modes of a frequency stabilised He-Ne laser.

A lifetime measurement of the h, i, j hyperfine components of the R (127) line of the 11-5 band of the B 3Π ou+-X 1Σ og+ electronic transition in the iodine molecule

An average lifetime of 380 ± 15 ns for the h, i, j, components of the R(127) line in the 11-5 band of the B 3Π ou +X 1Σ og + electronic transition in 1 27 2 has been measured using an inclined molecular beam and a frequency stabilised He-Ne laser.

Dimensional stability of fused silica, Invar, and several ultralow thermal expansion materials

A method is developed for testing the long-term dimensional stability of an iodine-stabilized He-Ne laser, using a technique whereby thermal expansion coefficients are measured by forming a Fabry-Perot etalon from the sample and monitoring the optical resonant frequencies with tunable sidebands impressed on a laser beam from a frequency-stabilized He-Ne laser. A change of 1 ppm over a 3-yr period on the part of fused silica dimensions and the differential thermal expansion of Invar LR-35 and Super Invar materials are noted. The method is of interest for the metrology of extremely stable structures such as telescopes and optical resonators.

沃素の飽和吸収を用いたHe-Neレーザの周波数安定化

Hoping to develop a future primary standard of length to use for precision interferometric length measurement, a frequency-stabilized He-Ne laser has been made. The frequency of the 0.633μm output is locked to one of the hyperfine components of an absorption line of moleculer iodine 127I2 by the method of saturated absorption.The laser cavity in which the absorption cell of iodine is placed, is servo-controlled by dual feedback loops; one is for proportional control by a piezoelectric transducer, and the other is for on-off control driving a specially designed fine tuning apparatus with a parallel spring system until the servo error is reduced to less than a set value.The stability of the frequency is evaluated by Allan variance and standard deviation measurements of the beat frequency between two stabilized lasers. Results of the measurement for five hours and a half give an Allan variance of 8kHz for a 10 second averaging period and a standard deviation of 96kHz. From these data, long term stabilities of 1.2×10-11 from the Allan variance and 1.4×10-10 from the standard deviation are evaluated for the individual laser.The relations between the temperatures of molecular iodine in the absorption cell and of the laser output, between the maximum frequency deviation of the modulated laser output and the first and third derivative signals of inverse Lamb dip produced by saturated absorption in iodine vapour are obtained. And systems for measuring the beat frequency by analogue and digital methods are described.