I have fabricated a back gated device. I want to use a laser light to measure the IV characteristics under laser illumination. For this purpose, I have to illuminate the 5 um channel of my device.
The problems are:
We have a laser source which we have never used for this purpose. So we don't know to focus light in the channel region.
It is a high power laser that can burn the sample.
How to focus the light?
How to decrease the power?
Expand the beam first. Then use techniques from projection photolithography. For this you need to first fabricate a chrome mask which has a line (opening) that is close to 5 micrometers (or a narrow slit made of metal with the same 5um opening width may work). The expanded laser beam should fall on this mask. Projection optics need to be used so that the ~5um wide light beam emerging from the projection optics will fall on the channel for which you need the IV characteristics determined. Such a technique will minimize diffraction issues if the proper optics are chosen.
In order to decrease the power of laser source, you could use optical attenuator, such as film samples or photonic crystal.
In order to focus the laser beam, ordinary optical components, such as lenses, can be easily used to do so.
But I would like to suggest using a choppers to convert the laser beam into pulse mode in order that device to respond to the variation in the incident intensity with time.
Muhammad Farooq Reflection losses, the spectral characteristics of the light source and numerous other efficiency-limiting factors, such as incomplete light absorption and leakage current.
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