Saturated Absorption In Iodine Research Articles

International Comparison of Two Iodine-stabilized He-Ne Lasers at λ ≈ 543 nm

An intercomparison of two 127I2 stabilized He-Ne lasers at λ ≈ 543 nm, recommended as length standards, has been made between the DFM and the PTB, and is the first international comparison at this wavelength reported so far. Both lasers use saturated absorption of iodine in an external cell, one (PTB) using frequency-modulation spectroscopy, the other (DFM) using the first or third harmonic detection techniques. The range of the frequency differences between the two lasers was from 11,8 kHz to 18,4 kHz, with a mean of Δf = 14,2 kHz and a standard uncertainty of 1,9 kHz. A minimum value for the two-probe relative standard uncertainty of 2,5 × 10-13 (140 Hz) is reached after 5 000 s. The hyperfine line splittings were measured by the beat-frequency technique, and good agreement was found between the two completely different laser systems. Measurements of frequency dependence on modulation amplitude, iodine pressure, and pump power are also reported.

A new type of iodine cell for stabilized lasers

The frequency of a laser stabilized by saturated absorption of iodine is a function of the iodine pressure in the cell. This pressure is usually set by the temperature of a cold finger attached to the cell. A simplified type of iodine absorption cell which has no cold finger and in which the iodine pressure is set at the time of filling is reported. Such a cell exhibits a much weaker frequency dependence as a function of temperature than does a normal cell and appears to show good long-term stability. >

He-Ne Lasers Stabilized by Saturated Absorption in Iodine at 612 nm

In this report we compare the metrological potential of two 612-nm He-Ne lasers stabilized by saturated absorption in iodine. In the case of stabilization to an internal cell, the device easily produces high-contrast resonances but has some drawbacks such as a strong power broadening of the iodine lines, and the presence of weak parasitic lines. In the case of stabilization to an external cell, strong and narrow signals are obtained. This system is promising for an improvement of frequency stability and reproducibility.

Helium–neon laser stabilized by saturated absorption in iodine at 612 nm

Hyperfine structure of iodine has been studied at 612 nm by the technique of saturated absorption in an iodine cell placed in a He-Ne laser modified to operate at this wavelength. The most interesting feature of the laser is the existence of strong inverted Lamb dips at a very low vapor pressure, which provides very good short term frequency stability. Some factors which limit the reproducibility of the device are also investigated.

Preliminary experiment for stabilizing unmodulated He-Ne laser to an iodine hyperfine component

First- and third-derivative signals of saturated absorption in iodine 127 molecular vapor are detected by using a frequency-modulated 190-cm-long 633-nm He-Ne laser with a Fox-Smith–type resonator and an iodine absorption cell which is set outside of the resonator. Aiming to stabilize the laser with unmodulated output, a retroreflector-type optical modulator is added to the above system, and the first-derivative signal is obtained by external modulation. Comparing the obtained signal with those obtained by the frequency-modulated laser, possibilities to detect the third-derivative signal by using the optical modulator and to stabilize the unmodulated laser are found.

New Developments in Iodine-Stabilized He-Ne Lasers

The improvement of the performance of a 633-nm He-Ne laser stabilized by saturated absorption in iodine, which results from heating the iodine cell is described. A simple modification of the laser which permits frequency-stabilized operation at two other visible wavelengths which may be useful for interferometry is also reported.

International intercomparison of the wavelength of iodine-stabilized lasers

The wavelengths of He-Ne lasers stabilized by saturated absorption in iodine and designed at BIPM, NPL, and PTB have been compared simultaneously by beat frequency measurements. The intention of the comparisons was to get experience about the reproducibility of differently designed lasers. All lasers were stabilized by third harmonic locking but with different electronic circuits. Among other effects, the reproducibility appears affected also by a modulation amplitude dependent shift of the laser frequency f. For a suitable range of modulation amplitudes the reproducibility of the four investigated lasers has been estimated to be ±4 × 10−11 f.

Current state of the problem of the definition of the meter

Possible ways of increasing the accuracy of definition of the meter in terms of the wavelength of laser radiation are discussed. A review is given of published work on saturated absorption of laser radiation in iodine and methane and on measurements of the wavelength of stabilized lasers in the visible and infrared regions of the spectrum. Values are reproduced for the wavelengths of lasers stabilized by saturated absorption in iodine and methane and for the velocity of light, which have been recommended as standards for measurements of length and wavelength by the Comite Consultatif pour la Definition du Metre (CCDM) of the Comite international des Poids et Mesures.