Stabilized (3)He-(20)Ne transverse Zeeman laser

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.

Frequency stabilization of an internal mirror He-Ne laser with a high frequency reproducibility

A method has been developed for the stabilization of an internal mirror He-Ne laser to achieve a high frequency reproducibility that is mainly influenced by the temperature of the stabilized laser. However, it is difficult to achieve a reproducible temperature in a short time under different ambient temperatures. In this paper, the He-Ne laser is stabilized based on the relationship between the laser mode number and the laser cavity temperature where a reproducible temperature can be rapidly achieved under different ambient temperatures, resulting in a high frequency reproducibility. Experiments have demonstrated that the He-Ne laser used can be stabilized in approximately 10 min, typically 6 min; the frequency stability is less than 2×10(-10); the frequency reproducibility is less than 1×10(-9).

Frequency stabilization of internal-mirror He-Ne lasers by air cooling

Instead of the traditional heating method, the cavity length of an internal-mirror He-Ne laser is controlled by air cooling which is implemented by a mini cooling fan. The responsive property of the cooling fan and the thermal expansion of the internal-mirror laser tube are investigated. According to these investigations, a controlling system is designed to drive the cooling fan controlling the cavity length of the laser. Then the frequency is stabilized by comparing the light intensities of two operating longitudinal modes. The results of beating with an iodine stabilized He-Ne laser show that a relative uncertainty (Δf/f-) of 4.3×10(-9) in 5 months, a frequency fluctuation of <1.4 MHz, and an Allan deviation of 6×10(-11) (τ=10,000 s) in 20 h are obtained.

Frequency stabilization of a green He-Ne laser

A new process for stabilizing the frequency of commercially available 543-nm He-Ne lasers is described. The stabilization method is based on anomalous dispersion of the gain medium. A total of four green lasers have been stabilized-two at the National Institute of Standards and Technology and two at the Institute of Scientific Instruments of the Czech Academy of Sciences-making it possible to study frequency variations of the lasers relative to each other. We have also stabilized a 633-nm laser by the use of the same method used for 543 nm.

Use of the beat frequency between two modes for frequency stabilization of internal-mirror lasers

We present a simple method of frequency stabilization of a laser with two orthogonal modes that uses the effects of anomalous dispersion at the active line. The result of this effect is that the frequency difference between oscillation modes varies during the frequency tuning along the Doppler line of the transition and has its minimum or maximum when the modes are symmetrically placed around the central part of the gain curve. We applied the semiclassical approach to describe the laser, and we established the rules for laser parameters to obtain the most convenient conditions for stabilization. We stabilized the thermally compensated experimental laser tube and reached frequency stabilities of 3 × 10(-9) and 3 × 10(-10) for integrating times of 1 and 134 s, respectively.

Frequency stabilization of a He-Ne laser using lateral stress

Frequency stabilization of an internal mirror He-Ne laser by a new simple method is reported. In this method, the laser cavity length is modulated by stretching the front part of the laser tube using lateral stress; in this way the laser cavity length is stabilized on the Lamb dip. The relative frequency stability is +/-4.1 x 10(-9) over 1 h or longer.

Optical phase fluctuations thermally induced in a single-mode optical fiber

Mathematical expressions have been derived on fluctuations of optical phase and frequency of a light wave which are thermally caused in a single-mode optical fiber in terms of fiber length, thermal coherence length, and fluctuation frequency. Fluctuations of optical phase and temperature were measured at a wavelength of 0.6328 microm by Mach-Zehnder interferometry, and the results are compared with theoretical predictions. A minimum detectable temperature change through optical phase shift depends on frequency stability of a source laser. It is 10(-5) K with a fractional frequency fluctuation of 10(-9).

Frequency stabilized lasers: optical feedback effects

Two simple systems have been described for stabilizing the frequency of a 2-mW internal mirror 633-nm He-Ne laser. This paper shows that small amounts of optical feedback will seriously reduce their performance. Their relative sensitivity to optical feedback from a plane mirror is compared.

Frequency stabilization of a 0.633-microm He-Ne longitudinal Zeeman laser

A new method of stabilizing the output frequency of a He-Ne laser in a longitudinal magnetic field has been developed. With simple modifications to a standard He-Ne laser tube we obtain a frequency stability of <1 MHz (<10(-9)) for an averaging time of 1 sec and a long term (5 months) frequency reproducibility of ~ +/-1 MHz.

Stabilized transverse zeeman laser as a new light source for optical measurement

The light emitted by a stabilized 633-nm He-Ne transverse Zeeman laser (STZL) is composed of two linearly polarized components that are perpendicular to each other. Optical frequencies of the two components are different, and therefore the light changes its polarization with time. The change is represented on the Poincaré sphere as a spin along the equator containing S(2) and S(3) axes of the sphere. Three types of polarimetry and two types of interferometry using an STZL are proposed and experimentally demonstrated. Comparisons of these techniques with the existing ones are also reported.