Hi all, I'm a student at a mechanical engineering faculty, and I'm doing my final project now. The purpose of the project is to built a sensor for measuring gravity-capillary waves in a wind-wave flume. The idea is to pass a laser beam from beneath of the aquarium through the aquarium bottom, through the wavy water, up to the air over the water and at the end the laser beam should point on a PSD (Position Sensetive Detector) which measures the X and Y deflections of the beam from the calibrated point over still water. Then I can use Snell law and various DSP to find the wave coeficient 'k' or waves wave lengh 'lamda', phase velocity 'C' etc... As part of a project, I need to draw a circle with the laser beam (using a rotating mirror) with a diameter of 1.5mm over the water surface. The smallest laser beam diameter I could find is 0.48mm and it's too big! I'm going to use a NeHe 632.8nm 5mW or 10mW CW laser, and I thought to use a beam expander reversibly as a beam condenser, and here is the question: Is it possible to pass a 0.48mm diameter laser beam through a beam condenser X10 to receive a 0.048 diameter laser beam without loosing the needed energy to pass through the perspex of the aquarium and the water, so the PSD will detect the beam? Thank you for you attention, Gary.