No abstract

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.

This paper presents a measurement system that can measure micro displacement by laser interference and image process methods. The displacement is measured by testing the relative moving distance between the movable mirror and the fixed mirror. Based on Michelson interference theory, the interference stripe images produced by a monochromatic laser source is collected by the CCD, which is used in the system to track the motion of PZT. The curve of light distribution is analyzed and dealt by Fourier Transformation and Low-pass Filtering methods. Least Squares Fit method is used to get normal amplitude, angle frequency and phase of the curve of light distribution and account the change of phases. Appling this measuring system, the micro-displacement is measured and obtains good test results.

An intercomparison has been made of the frequencies of He-Ne lasers stabilized using intracavity saturated absorption in '2712 at 633 nm. Lasers at ten standards laboratories (PEL (New Zealand), NRC (Canada), NBS (USA), NPL (UK), PTB (FRG), NPL (India), NIM (China), NRLM (Japan), KSRI (South Korea), and NML (Australia)) were each compared in turn with a portable laser from PEL during March to May 1984.The optical frequencies of all participating lasers exhibited a standard deviation of 23 kHz (5 parts in 10") with a range of k 40 kHz. This standard deviation is a factor of seven smaller than the standard deviation of the absolute value recommended for the optical frequency of these lasers. If allowance is made for one iodine cell believed to be contaminated, the standard deviation is reduced to 18 kHz. Power-shift coefficients were measured, and ranged from + 1.4 kHz/mW to -6 kHz/mW, referred to intracavity power.It is concluded from the measured frequency offsets and power shifts that the best frequency reproducibility amongst different designs of laser is likely to be obtained at low levels of intracavity beam power ( 5 -10 mW). The frequency reproducibility was not improved by extrapolating to zero power.

Lasers from three national metrological institutes (NMIs) have been measured following the protocol of the BIPM.L-K11 ongoing key comparison initiated by the Comité Consultative des Longueurs (CCL) 11th meeting in 2003. The absolute frequency of the f component of the R(127) 11-5 transition at 633 nm was measured for two of these lasers in their home institutes, AIST/NMIJ and UME, while the b5 component of the R(106) 28-0 transition at 543 nm was measured on a standard from NIM at the BIPM. The results of these measurements are compiled in the present paper. The comparison reports, as communicated by each participant, are included as Appendices.Main text. To reach the main text of this paper, click on Final Report. Note that this text is that which appears in Appendix B of the BIPM key comparison database kcdb.bipm.org/.The final report has been peer-reviewed and approved for publication by the CCL, according to the provisions of the CIPM Mutual Recognition Arrangement (MRA).