A optical pickup unit from a blueray player or HD-DVD has a 405nm laser diode with the wavelength optimized optics inside like a collimator, focus actuator and a photodiode array for checking the focus.
One problem is a diffraction grating that is behind the lens that is there to create the tracking sidebeams. They might create optical leakage and inadvertently expose parts of the PCB.
Another problem is the spot focusing, the spot size for blueray is around 800nm, so you need a way to track while not completely in focus or just choose a fixed focus and hope for the best.
The focusing actuator can be controlled by the actuator driver on the drive PCB, but you can use a high power opamp like the L2722. The datasheet contains some example schematics on bidirectional control of inductive loads. Best would be to use a TDA7073, unfortunatly that chip is obsolete but made for the task.
--- In Homebrew_PCBs@yahoogroups.com, "Jeff Heiss" <jeff.heiss@...> wrote:
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> A DVD laser is IR and a CD laser is red. Would the optics from the lasers
> work for UV?
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> Jeff
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> _____
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> From: Homebrew_PCBs@yahoogroups.com [mailto:Homebrew_PCBs@yahoogroups.com]
> On Behalf Of Dave Sage
> Sent: Friday, February 24, 2012 1:16 PM
> To: Homebrew_PCBs@yahoogroups.com
> Subject: [Homebrew_PCBs] Re: Novel way to expose photo resist??
>
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> I presume a CD or DVD burner has all the optics required to focus the laser
> diode to a very tiny spot. Maybe it's just a matter of swapping out the
> diode for an ultra-violet version. Also concerning not being able to see it;
> I know the coating inside fluorescent tubes converts a lot of ultra-violet
> to visible light. Maybe a target made form a piece of coated glass could be
> made to "see" the dot at least long enough to focus it if required.
>
> Sage
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