Laser has been widely used in spectroscopic and metrological measurement. High-precision laser metrology is affected by the refractive index of air. In order to apply the algorithm for the refractive index of air in some situation where low calculation complexity and high-precision are needed, the algorithm of the refractive index of Rueger is updated. As the errors of Rueger’s algorithm are mainly affected by temperature, humidity, and the concentration of carbon dioxide in the atmosphere as well as laser wavelength, we do some revisions about these effects of the factors of atmosphere in Rueger’s algorithm. The conditions of standard air is redefined in this paper because of the average concentration of carbon dioxide in the atmosphere has been changed in the past few decades. As the concentration of carbon dioxide in the air is not constant, the effect of carbon dioxide on the refractive index of air is taken into consideration in the updated algorithm. The updated algorithm adapts to the real atmosphere well. The effects of dry air and humid air on the algorithm are also corrected, and the refractive index of air calculated by the updated algorithm is much closer to that of Philip E.Ciddor’s algorithm defined as reference algorithm in the paper because of its high-precision. The performance of the updated algorithm is also analyzed in this paper. It is compared to that of the reference algorithm and the real measured data. Comparing results show that the performance of the algorithm has been improved after the correction. Comparing to the reference algorithm, the performance of the updated algorithm is a little bit lower, but the updated algorithm is much simpler and easier to be applied. Comparing to Rueger’s algorithm, the performance of the updated algorithm is much higher and the complexity of the updated algorithm increases very small. The updated algorithm meets low calculation complexity and high-precision requirements.
Moving mirror tilt, which causes misalignment of two reflectors, is a key issue in Fourier Transform Infrared
Spectrometer (FTIRS). Dynamic alignment system (DAS) is adopted to solve misalignment problem. High precision
detection of dynamic misalignment angle is one of the most important steps in DAS, mainly upon which the adjustment performances of DAS depend. A new measuring algorithm is presented which is based on amplitude detecting  between laser interference signals generated by reference laser source in this paper. Mathematical analysis is described and experiment results are shown. These results show that the measuring precision of 0.6 micro-radians of dynamic tilting angle is achieved with this method. This is a guarantee for a FTIRS to acquire high interference efficiency.
Dynamic alignment system (DAS) is used to correct the misalignment of moving mirror in Fourier Transform Infrared
Spectrometer (FTIRS) of which both fixed mirror and moving mirror are plane reflectors. The detecting precision of
dynamic tilting angle of moving mirror offers guarantees to the adjustment performances of DAS. In this paper, the noise
tolerance of measuring precision of tilting caused by moving mirror are theoretically analyzed and tested. Experimental
results show that tilting measuring accuracy is improved with adjusting methods according to the noise tolerance
A frequency stabilized system of the laser diode is described in this paper. It consists of two parts: the temperature
controlling module and the driving current modulating module. The principle and construction of the system are
analyzed. Experiments are conducted and data are obtained. It is found that the temperature stability is better than 0.01 K
and the stability of the current source is better than 10 uA.