I've finally had some time to think about hardware for the lensless imager, specifically the laser diode driver. I learned about the LM317T voltage regulator and how to use it as a constant current source at this site . Circuits based on this regulator seem to dissipate a lot of heat, but their simplicity makes them good starting points.

Basic holography requires very good light sources with high spatiotemporal coherence. Furthermore, the resolution of the imager will depend on wavelength, with shorter wavelengths giving higher resolutions. Unfortunately, high quality laser diodes that meet these rough specs seem to be a bit pricier than I expected, so I think it would be wise to test out the driver circuit on relatively cheap laser diodes to start. I don't want to buy an expensive laser diode and burn it out because I didn't understand the drive electronics.

One such cheap component is the ADL 65055TL red laser diode. This is a TO-can packaged laser diode that emits approximately 7 mW of laser light around 655 nm. More importantly, you can buy one of these from Farnell for about USD 3.50, so they would make great test sources.

I've done some basic calculations for the circuit design and will make a more detailed post once I've bought and tested the parts.

-kmd