We report two methods of modulation-free frequency stabilization of a laser to sub-Doppler atomic absorption line. The first one employs the magnetically induced sub-Doppler dichroism in cesium vapor cell based on Zeeman effect. The second one utilizes two acousto-optical modulators (AOM) as well as sub-Doppler spectra to generate dispersion-like signal. We compared the residual frequency fluctuation in preliminary stabilization with the case of free running. These two schemes can avoid the additional frequency noise as well as intensity noise due to the direct frequency dither on laser source.
There are two kinds of image in the field of imaging for the underwater target due to using two types of light source, respectively, continue green-blue laser and pulse green-blue laser. When pulse laser is used, the obtained image has the characteristic of low contrast, small dimension of target and complex background. The method of multiple correlation peak-value detection, which is based on the correlativity of pixels in the region of target, can be directly used to implement target detection for the underwater laser image. When continue laser is used in the process of imaging for the underwater target, there is a beam of strong light in the image, which makes it difficult to implement target detection. Therefore, we use the multi-scale and multi-channel Gabor filter group with the character of direction selection to depress the disturbance of the strong beam firstly, and then, use the multiple correlation analysis method to detect the weak target in the image. Experimental results show that these methods are practical and effective.
Second harmonic generation from 858nm to 429nm has been investigated at room temperature by using Potassium Niobate (KNbO3) crystal. The optimum parameters for nonlinear conversion in our designing singly resonant, external ring cavity pumped by the Ti: Sapphire laser are established. In addition, we investigate the conversion efficiency over a range of operating conditions. When the cavity is scanned, 170 mW (235mW corrected for losses of the output mirrors) of blue light at 429nm is produced with 600mW of pump power near 858 nm whereas 137 mW is generated with 565 mW of pump when the cavity is locked.
The third-derivative saturation absorption spectrum (SAS) of cesium D2 line is demonstrated via the third-harmonic technique by applying the frequency modulation to an external AOM (acousto-optical modulator). By employing the frequency discrimination of the third-derivative SAS, frequency of DBR diode laser at 852nm is locked to the hyperfine component of cesium 6S1/2F = 4 ? 6P3/2F' = 4,5 . Frequency jitter of less than in 10 seconds is estimated based on the error signal after locking in the preliminary stabilization.
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