Laser-module and driver
For the laser module I choose a relatively cheep heat sink and a standard 3-layer glass lens (450 nm) and a Osram PL TB450B 1.6 W_opt. 450 nm diode from China. The lens came in a package with the heat sink.
As the power source for the laser I am using a constant current power supply (max. 3W) with TTL support.
First I had to unsolder all plastic sockets from the board since I could not find the matching connectors online. I replaced them with common 2-pol Molex sockets and made my own connectors with cables.
To adjust the current the laser will get, I adopted the idea of a dummy diode from power-LEDs (dummy LEDs).
A BD809 was mounted on a good heat sink and a 20 mA LED + 470 ohm resistor was soldered to base and collector of the transistor.
With this dummy laser diode I could adjust the current without risking my Osram diode. The transistor converts all energy into heat, so with 1.2 A @ about 4.2 V which are typical parameters for the laser diode it generated
about 5W of head. There is no arguing about whether that a heat sink is necessary !
To switch the laser on/off by grbl, I connected the TTL- pin to a common ground with the arduino and the TTL+ pin with a pull-down resisitor to pin11 (grbl 0.9) of the arduino. By variating the spindle spped with the S<number> g-code paramter a PWM signal controls the on/off time of the laser and resulting in <number> % of power.
With the power source set up, I began to mount the diode itself into the heat sink. This was more difficult than I thought since there is very little space for the cables and the isolation of the pins.
With the cables finally soldered to the diode, I applyed a tiny amount of silver thermal paste to the diode. The data sheet states, that the main heat dissipation is done by the tiny metal ring around the diode.
I wanted to be sure the diode runs within thermal parameters (>70 °C).
For active cooling I removed the fan that came with the laser heat sink and mounted a very powerful 4 cm fan on it. This fan not only cools the laser, but also blow all smoke from cutting/engraving away.
So nothing can condensate on the glass lens.