The uniformity measurement, transmittance and reflectance of the optics in other words, is one of the essential
specifications for those large optics of high power laser facilities. Both high reproducibility for large-size and precision
with wide dynamic range make such testing a real challenge to take.
In this paper, a transmittance and reflectance measurement system with large aperture is demonstrated. With a laser
source at 1053nm, three kinds of large aperture optics are tested by conventional direct detection. The results show that
this system can realize high measuring precision (0.05% and 0.01% for transmittance and reflectance respectively) when
tested parameter is small in value. In addition, the measurements precision with 532nm and 351nm laser sources are also
tested compared, and the factors of measurement uncertainty with shorter wavelength are analyzed.
To further promote accuracy and signal-noise ratio, coherent heterodyne detection and optical demodulation technique is
proposed especially for high transmittance measurement. A demonstrative experiment of transmittance detection by
balanced heterodyne and optical demodulation is performed, and a SD=0.052%, which is more than two order precision
is achieved. It results that it is valid compared with conventional direct detection, and gives a promising method for
higher precision during further practical applications.
Proc. SPIE. 9142, Selected Papers from Conferences of the Photoelectronic Technology Committee of the Chinese Society of Astronautics: Optical Imaging, Remote Sensing, and Laser-Matter Interaction 2013
KEYWORDS: Signal to noise ratio, Superposition, Photodetectors, Prisms, Sensors, Silicon, Interference (communication), Data acquisition, Environmental sensing, Temperature metrology
To accurately measure the linearity of photodetectors in near-infrared waveband, based on the beam superposition method, a new design idea which use the tow-beam path and correlation methods was proposed. Using the 1053nm laser, and the Si photodetector as the experimental subject, a linearity measurement system of highly accurate photodetectors was designed. This system has over seven orders of magnitude dynamic range. The joint uncertainty is superior to 0.08%. Meanwhile, the linear factor of four different conditions which include the different size of incident beam spots, incident angles, positions and the environment temperature have been measured and analyzed. The experiment shows that the linearity of Si photodetector is ideal when the size of beam spots are bigger, the incident angles are smaller and the environment temperature is lower, moreover, the linearity of margin area is unsatisfactory.
Transverse stimulated Raman scattering (TSRS) gain coefficient of a KDP sample is measured by improved methods.
The improvements include color separation of TSRS, noise light management and acquisition of valid TSRS temporal
pulse. After extracting TSRS temporal pulse and data analysis, we obtained a TSRS gain coefficient of
0.28±0.03cm/GW for the KDP sample. Our improvements of measurement method include the following three aspects:
First, the separation of TSRS irradiation (362.2nm) from Rayleigh irradiation (351.15nm) is realized by first-order
diffraction of grating for TSRS and Rayleigh. Second, to improve the ratio of TSRS signal and noise light owing to
spurious reflection of pump radiation, we remove noise light by using band-pass filter and absorption traps. Third, by
analyzing the time delay between pump signal and noise signal, we demonstrates the valid TSRS temporal pulse can be
extracted from the noise signal and used to calculate the TSRS gain coefficient of KDP.