Experimental studies on operational characteristics of two kinds of avalanche photodiodes (APD) have been carried out for the application to the photon counting method. To achieve high sensitivity, it is necessary to operate the APD at the optimum bias voltage at liquid nitrogen temperature, because at this temperature the counts of noise pulses can be reduced considerably. Also precise measurements of the photoelectron pulse height distribution are required in order to determine the suitable threshold voltage for the pulse height discriminator in the photon counting operation. Under the above consideration, a linearity between the optical input intensity and the photoelectron counts was obtained in the range from about 10^-10 W to 10^-15 W.

View full abstract

Effect of laser wavelength fluctuation on the data obtained by a fringe counting laser interferometer, being utilized for measurement of the line standard at NRLM, is experimentally studied by means of the Allan variance of the fluctuation. The fluctuation of the light source for the interferometer (Spectra-Physics Model 119) is measured from the beat note with the iodine stabilized He-Ne laser of NRLM. It is founded that the flicker FM noise for r>150 ms plays a dominant role to the measurement error due to the fluctuation and the standard deviation of measured value with the interferometer is estimated to be less than 3.5×10^-8. √N/ (N-1) for τ=600s (typical measuring time for 1m line standard), where N is number of samples.

View full abstract

The longitudinal modes of a internal mirror He-Ne laser was collapsed into one by a transverse magnetic field. The laser frequency was then stabilized by referring to the frequency of the beat of light components which vibrate in and perpendicular to the transverse magnetic field (intramode beat frequency) The frequency fluctuation of the laser was evaluated by optical beating with an iodine stabilized laser of the National Research Laboratory of Metrology. The fluctuation was proved to be smaller than 1×10^-10 at accumulation period of 3×10^-2 sec by Allan variance. Two types of developments were introduced to the regulation system, and the results were evaluated by Allan variance analysis of the residual signal. The frequency fluctuation of the laser stabilized by the air tight system was 7×10^-11, and that of the laser stabilized by the automatic resetting system, which adjusts the working point of a proportional regulation system so as to keep the intramode beat frequency measured by a quartz controlled counter to a preset digital number, was 2×10^-11.

View full abstract