Helium-neon laser frequency

An alternative, proposed by R. Kallenbach, employs two tunable dye lasers, operating at the fourth and sixth harmonic of the 3.39 pm helium neon laser frequency f. The frequency ratio of 3 2 is assured by comparing the second harmonic of the laser at 6f with the third harmonic of the laser at 4f. The frequency difference is simultaneously maintained at 2f by monitoring a beat signal between the sum frequency 4f+f and the difference frequency 6f-f. Summing the frequencies 6f and f finally produces 0.485 pm radiation at 7f. 

In 1972 a 100-fold increase in the accuracy of the known speed of light was achieved by measuring the frequency of a helium-neon laser line in terms of the Cs time standard (Appendix Table A.2) and measuring its wavelength in terms of the Kr length standard. [K. M. Evenson et al., Phys. Rev. Letters, 29, 1346 (1972).] The improved value is... 

One interesting reference standard may be the methane stabilized helium neon laser at 3.39 pm. Its infrared frequency can be compared directly with the microwave cesium frequency standard with the help of a relatively short frequency chain [32], An accuracy of 1 part in 1012 or better appears feasible for a transportable secondary standard. 

Figure 7 Experimental signal recorded for photolyzed MbCO. Fe-ligand vibrations dominate the cluster of modes observed in the 230-270 cm region. The clearly resolved frequency separation between the in-plane Fe-N, yr frequencies at 251 and 267 cm reflects the asymmetric interactions with the histidine ligand. The Fe-histidine stretching frequency appears at 234cm L Data were recorded under continuous illumination by a 15 mW helium neon laser with k = 633 nm. The temperature of a sensor mounted in the sapphire sample block was 15 K...

The data acquisition rate (sampling frequency) for mid-IR interferograms is usually equal to the frequency, Hz, of the interferogram that is generated by a laser (usually a helium-neon laser at 632.8nm) simultaneously with the infrared interferogram. f is equal to the product of the wavenumber of the laser and the... 

Another important advantage of FT-IR spectrometers is their outstanding frequency accuracy (Connes advantage), the basis for all achievements in difference spectroscopy. This accuracy of spectral frequencies is due to the precise and stable collection of the interferogram signal, triggered by the helium—neon laser. An accuracy in wavenumber of better than 0.01 cm can be achieved. 

Infrared spectra were obtained on a Digilab FTS-15/B spectrometer. Four hundred scans at a resolution of 2 cm l were signal averaged and the spectra were stored on a magnetic disc system. The frequency scale was calibrated internally with a helium-neon laser to an accuracy of 0.2 cm l. Spectra recorded at elevated temperatures were obtained using a SPECAC high temperature cell and controller mounted in the spectrometer. 

Fig.13.12, Saturated absorption on the 6328 A transition of a helium-neon laser. (a) Neon absorption tube inside laser resonator. (b) Output power as a function of oscillation frequency showing saturated absorption resonance superimposed on normal Gaussian envelope. (After Lee and Skolnick (1967).)...

The mirrors of a 6328 X single-frequency helium-neon laser are separated by a spacer formed from a cylinder of fused quartz 14 cm long. The entire laser is enclosed in an oil-bath whose temperature is maintained constant to within 0 01 °C. Calculate the frequency stability expected for this device given that the linear... 

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