Gaussian Beam Effect on Equivalence Principle Test Using Free—Fall Interferometry

We discuss the gaussian beam effect on the test of the equivalence principle using a free-fall interferometer.A two-lens assembly is used to improve the propagating character of the laser beam,and the beam radius is collimated to about 3.0mm.The analysis shows that the gravity acceleration difference induced by the Gaussian beam effect could be less than 10^-15 g for our double free-fall experimental design,but it would be 10^-9g for the absolute measurement of the gravity acceleration with the usual single free-fall method.     

Numerical Simulations on the Formation of Speckles in Nanofluids Illuminated by a TEM00 Laser Beam

On the basis of a Rayleigh scattering model for a single nanoparticle illuminated by a TEMoo laser beam, we theoretically and numerically study the speckle formation when nanofluids are illuminated by a TEMoo laser beam. The results show that the laser speckles possess a Gaussian distribution, which are in agreement with the experimental results. The results may be useful for using a laser speckle velocimetry to determine the velocitiies of nanoparticles in nanofluids.