Single-mode He-Ne Laser Research Articles

Self-mixing interferometry based on nanometer fringes and polarization flipping

Self-mixing interferometry (SMI) based on nanometer fringes and polarization flipping is realized. The interferometer comprises a single-mode He-Ne laser and a high-amplitude reflectivity feedback mirror. The nanometer fringes are obtained by tilting the external feedback mirror. The fringe density is 35 times higher than that derived with conventional two-beam interference, and each fringe corresponds to a λ/70 displacement in external cavity length. Moreover, polarization flipping occurs when the external feedback mirror moves in the opposite direction. Such movement can be used to easily distinguish displacement direction. Experimental results show an optical resolution of displacement measurement of 9.04 nm with a range of 100 µm. The proposed SMI presents promising application prospects in precisely measuring displacement and calibrating other micro-displacement sensors because of its optical wavelength traceability.

Optical feedback signals involving the misalignment information

The optical feedback characteristics of the laser intensities at both emission directions are studied in a single-mode HeNe laser under low optical feedback strength. The sign inversion phenomenon can be observed when the photodetector at the main emission direction only receives the main light spot. There is no sign inversion phenomenon but intensity branch phenomena or fringe frequency-doubled phenomenon when the photodetector at the main emission direction receives both the light spots. When the optical feedback signal has intensity branch, it involves the misalignment information of the external cavity which can be used to detect the angular pitching of the reflector. The fringe frequency-doubled phenomenon can be used to double the resolution of an optical feedback system.

Properties of a phase-conjugate etalon mirror and its application to laser resonator spatial-mode control.

The concept of a phase-conjugate etalon mirror consisting of one flat and one aspheric surface is introduced. This new element can be used as an end mirror of a conventional resonator to promote spatial-mode selection and mode shaping. A phase-conjugate etalon designed for the fundamental Gaussian mode is experimentally implemented and tested with a single-mode He-Ne laser.

Optical feedback laser with a quartz crystal plate in the external cavity.

We studied the optical feedback characteristics of a single-mode He-Ne laser with a quartz crystal plate in the external cavity. The fringe frequency of the laser system can be doubled when the quartz crystal plate is positioned at a certain angle between the crystalline axis and the beam in the crystal plate. Theoretical analysis shows that the birefringent effect of the quartz crystal plate and the laser beam's second pass through the external cavity result in this phenomenon. The experimental results are in good agreement with the theoretical analysis. A quartz crystal plate can double the resolution of a self-mixing sensing system.

Chaotic Oscillation in a Single-Mode Class A He–Ne Laser (6328 Å) II

Chaotic oscillation in a single-mode He-Ne laser (6328 Å), which belongs to a class A laser, is investigated through experiments I which were reported in our previous paper [F. Kuwashima, I. Kitazima and H. Iwasawa: Jpn. J. Appl. Phys. 37 (1998) L325.], and the improved experiments II. The results of experiments II, which were conducted using a neutral density (ND) filter instead of the tilted mirror used in experiments I, demonstrate the effect of the tilted mirror and a pumping parameter on the chaotic behavior of this laser. We also confirm and discuss the threshold value for chaos vs control parameters from the estimated Lyapunov exponents. The route to chaos in this laser is also discussed. Lastly, the laser equation of the class A laser with delayed feedback is introduced and numerical results which reveal chaotic oscillations are reported.

Determination of the second-order susceptibility of ammonium dihydrogen phosphate and α-quartz at 633 and 1064 nm

The second-order susceptibility d(36) of ammonium dihydrogen phosphate (ADP) was determined from phase-matched second-harmonic generation (SHG) at two wavelengths. A cw single-mode He-Ne laser (λ= 633 nm) and a cw single-mode Nd:YAG laser (λ= 1064 nm) were used as fundamental beam sources. The results were d(36)(ADP, 633 nm) =(1.31 ± 0.05) ×10(-9) esu = 0.55 ± 0.02 pm/V and d(36)(ADP, 1064 nm) = (1.10 ± 0.06) × 10(-9) esu = 0.46 ± 0.03 pm/V. The d(11) values of α-quartz were determined relative to d(36)(ADP) to be d(11)(α-quartz, 633 nm) = (7.4 ± 0.3) × 10(-10) esu = 0.31 ± 0.01 pm/V and d(11)(α-quartz, 1064 nm) = (7.1 ± 0.3) × 10(-10) esu = 0.30 ± 0.01 pm/V by the use of the Maker fringe method. The Miller's delta ofADP and α-quartz is in good agreement at the two wavelengths.

Compact confocal interference microscopy

A compact form of confocal interference microscope using a single mode HeNe laser is described. Confocal operation is ensured by permitting the image light to re-enter the laser cavity. The confocal signal is detected as a modulation on the lasing power. Interference contrast images with lateral resolution 0.4 μm and height resolution 0.1 nm have been obtained using both dc and modulation feedback techniques.

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).

Stabilization of single frequency internal mirror He–Ne lasers: comment

In the cited article the frequency stability of a singlemode He-Ne laser is concluded from the stability of the laser intensity. We point out that this derivation of frequency stability may show remarkable systematic errors.

Optically controlled Fabry-Perot interferometer using a liquid crystal light valve

We report an optically controlled Fabry-Perot interferometer which uses a liquid crystal light valve (LCLV) for one of the mirrors. The light valve rotates the plane of polarization for light incident on its read side through an angle dependent on the intensity of a write beam incident on its other side. The Fabry-Perot interferometer is constructed using a polarizing cube beam-splitter and a second mirror. The finesse of this Fabry-Perot varies sharply with the rotation angle introduced by the LCLV. The dependence of this rotation angle on the incident write beam intensity varies with the frequency of the voltage applied to the LCLV, the bias voltage, and the orientation angle of the LCLV. Experimental performance is examined using a single mode He-Ne laser beam and compares well with theoretical predictions: This device has potential uses in optical computing and optical neural networks.

Picosecond time-resolved photoelectric correlation measurement with a photon-counting streak camera

An essentially new method of picosecond time-resolved photoelectric correlation measurement with a newly developed photon-counting streak camera (Hamamatsu C2909) is proposed. By this method temporal and spatial coherence of a quantized radiation field can be measured simultaneously. Statistical properties of a single-mode HeNe laser field (632.8 nm) have been examined quantitatively. The Poisson distribution of the laser field has been observed down to the time domain of about 10 ps.

Zero-field level crossing of the 633 nm Ne line in resonance absorption

The authors have investigated the zero-field level crossing lineshape in resonance absorption. A single-mode HeNe laser beam at 633 nm is applied to an external neon-gas absorption cell in a longitudinal magnetic field. They compare the measured lineshapes with theoretical predictions. Two superposed nonlinear Lorentzian-shaped resonances, known as the population effect of the 2p4-3s2 transition and the Zeeman coherence effect of the lower 2p4 level, appear on the background caused by the inhomogeneous broadening. Taking into account the background and the power broadening the authors obtain the linewidths at zero pressure gamma (2p4,3s2)=(7.7+or-2.1) MHz and gamma (2p4)=(8.4+or-1.2) MHz. For the neon pressure broadening the authors get for pressures below 200 Pa (1.5 Torr) d gamma (2p4,3s2)/dp=0.20+or-0.02 MHz Pa-1 and d(2p4)/dp=0.040+or-0.007 MHz Pa-1. Their values are in acceptable agreement with the values obtained with other spectroscopic methods.

Iodine stabilised He-Ne Laser

A single mode He-Ne laser operating at 6328 A is used with an iodine cell in the cavity to detect the absorption components of iodine falling within the gain curve of the laser line. Experimental details are given for locking the frequency of the laser line with one of the hyperfine components of the iodine absorption line, using a servo-control system. The system uses the technique of detecting the first and third harmonics of the modulation frequency.

Two-photon correlations in amplified laser light

The authors have measured the two-photon correlation function in 632.8-nm single-mode He-Ne laser light which had been amplified by stimulated emission in a long He-Ne discharge tube. For laser light intensities which were comparable with the discharge-tube spontaneous-emission intensity into a single mode, the measured correlations agree well with those predicted for a simple mixture of laser and chaotic light. The results are consistent with the assumption that laser light linearly amplified by stimulated emission has the same statistical properties as unamplified laser light.

Application of selective rotatable mirrors in a single-mode He-Ne laser with 100 mW output power

An investigation was made of the output power of a helium-neon laser (λ = 0.63μ,) with a resonator containing four standard gas-discharge tubes (two of these were taken from LG-38 lasers and two from LG-75). A system of selective rotatable mirrors, oriented at 45° with respect to the discharge axis, made it possible to halve the size of the laser and to suppress the competing emission at λ = 3.39 μ, so that the single-mode output power at λ = 0.63 μ exceeded 100 mW.

Homogeneous broadening in a 0.63 ?m single mode He-Ne laser

The expression for inversion density in a gas laser includes an additional term if one allows elastic and/or resonant collisions among the active atoms. This term is a function of the line parametersγ1, andγ2 and describes the effect of homogeneous broadening on the saturated gain profile. Measurements of these parameters show that the homogeneous broadening in a 0.63 μm He-Ne laser plays an important role.

Light Scattered from Thermal Fluctuations in Gases

A high-sensitivity high-resolution system for the study of light scattered from thermal fluctuations in gases has been constructed. A Bendix Channeltron photomultiplier tube with a dark noise of three-tenths of a photoelectron/second is the basis of an experimental setup which includes a Fabry-Perot interferometer having a bandwidth of 10 MHz with a piezoelectric scan and a frequency stabilized single-mode He-Ne laser. Resolution of 10 MHz is, therefore, attainable, and signal levels as low as six-tenths of a photoelectron/second yield reliable data. With this apparatus the density-density correlation function, G(r,t), of several gases has been investigated for a range of pressures. Whether the form of G(r,t) is derived from a kinetic or hydrodynamic view depends on the value of the Knudsen number, i.e., the ratio of λs, the wavelength of the scattering fluctuation, to the mean free path. Previous studies have concentrated on varying the angle of scattering (changing λs) while this study varies the gas pressure itself (changing the mean free path), allowing a more detailed investigation of the transition from the kinetic to the hydrodynamic view.

Frequency stabilisation of the He-Ne laser with an external Ne-absorption tube in an alternating magnetic field

A single mode He-Ne laser has been frequency stabilised with a relative frequency stability of 10−10 and an absolute accuracy of 10−9. The reference frequency is derived from a Ne-absorption cell in an alternating magnetic field. Theoretical analysis and experiments show that this high frequency stability can be achieved only with certain time-dependent functions of the alternating field and with the proper choice of the operating parameters of the laser and absorption tube.

On pressure broadening in a He-Ne laser

Evidence of the combined influence of disaligning and velocity-changing collisions on laser light-induced saturation peaks or holes in the velocity distribution of Ne <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2p_{4}</tex> atoms was obtained by transmitting 1.15-μ light of a short single-mode He-Ne laser through the discharge tube of a long single-mode Michelson interferometer-type He-Ne laser oscillating at 0.63 μ, and by measuring the frequency-dependent single pass gain of the IR light in the discharge of the latter laser. Atoms that have undergone a transition in the linearly polarized red-laser light field are partially aligned. The width of the detected signal depends on the He gas pressure and also on the mutual polarization of the two laser fields. This indicates a smaller velocity broadening for aligned atoms than for collisionally disaligned ones. An evaluation of the data provides information on the correlation of the above-mentioned collision processes and on phase-disturbing and phase-nondisturbing contributions to the line broadening. Estimate values of the integral elastic Ne <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2p_{4}</tex> -He scattering cross section and a cross section for phase shifting collisions are given.