Dear RG community.
I am trying to set up a fluorescent microscopic system for micro-PIV flow measurements. I am using a blue laser (473 nm) of 3mm diameter and I am expanding it using a 10X telescopic arrangement (collimated beam) before shooting it on to the epi-fluorescent prism cube. The flow is seeded with 1 micron green tracer particles. The laser is operating at the lowest power, and unfortunately the camera always shows this bright focused spot. I am unable to understand why this is happening.
Hi Dr. Shaik,
It sounds like you're experiencing an issue with a bright, focused spot in your fluorescent microscopic system. Have you tried adjusting the camera settings or changing the position of the laser? It's possible that the spot is caused by the laser being too strong or not being properly aligned with the prism cube.
Hello Rajan.
I have tried these options. The laser is operating at its lowest power and I still see this bright spot.
Hello subhani,
that is quite normal if your laser has high power (let's say 20mW or more). Due to the nonlinear dependence of laser power from the input voltage, the electronics can not get too low in power without getting an unstable output. As a consequence even the minimum power is definitely too much for focusing it in a single spot in an epi microscope.
The question is, do you want it in a single spot? or do you want to use your laser for widefield illumination? In the second case you should use a single lens instead of an expanding telescope, and make sure the lens focuses the laser on the back aperture of the objective, in order to obtain a flat and wide illumination on the sample.
If however you actually want your beam focused in a single extremely small spot, i would suggest getting a set of pretty strong ND filters, and try putting one or more of them before your expending telescope, so you can decrease the power by order of magnitudes
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