The laser beam passing through the focusing systems gets an facula,which consists of main spot and sidelobe on the focus plane.

Light intensity of facula increases when the diameter of the trees increases, and there lies a correctitude .

The results of output energy and pulse widths and the three-dimensional distribution of far field facula under different conditions were given.

According to this model,the parallel misalignment and angular misalignment can be calculated so long as light spot coordinate of PSD at two discretionary angles is measured.

The theoretical relation of position signal with the light spot is provided, and thus the tendency of experimental position signal contracting to the center of PSD gets good explanation when combined with background light.

The method can confirm the Gaussian distribution of optical intensity for the fundamental transverse mode of the He-Ne laser and determine the size of its light spot.

To adjust the infrared laser to the optimal place,we analyze and calculate the relation between the laser spot and the laser place.

As for certain material,we found that corresponding thickness and proper dimension of spot were necessary for accurately determining ultrasonic velocity.

The influence of knife-edge outline on the spot measurement is discussed and some theoretical results are shown in this paper.

To measure the laser facula in the far field using detector array,three requirements-laser energy density,the size of the array and the space be- tween detectors,are analyzed in the paper.

It is found that laser beam size has an important influence on the tempe.

In the paper we introduce the structure,operational principle and critical skills of the testing system for the laser beam through atmosphere.

Study on niobium-alloy diode-laser's faculae

Application of mode detection based on the minimum probability of Bayes in faculae removal in underwater V-groove weld