Savel brain dump in English!

As I mentioned, laser diodes are fragile devices. So the power supply must be adjusted before connecting any laser diode.

After all components are placed on PCB and visual inspection is finished, connect one 1.2K resistor in R4, R5 and R6 place. Power up the circuit. Check if linear regulator is working and we have stable 5V in the 7805 output. Measure voltage in the empty laser diode place. It must be less than 5V. Connect ampermeter instead of laser diode. Ampermeter must handle 1A current. In one position of the trimmer, the current in zero, in other some value. Set max current value by adding additional resistors in R4, R5 and R6 place. It is not very important to use exact resistor values in this circuit. Something in similar range is usable. I place 13K in R7 and everything is fine. Graduate trimmer to output current values.
Connect in series to ampermeter any powerful diode (I used optically burned laser) and check the current. It must be same as before and trimmer scale must be same.

This device must be powered to power source capable to output ~1A current at ~7V. If input voltage is higher (I use 12V Pb battery) the 7805 gets hot at max power. Use any heat sink to keep devices in working temperature.

Usage:

Connect (solder) laser diodes only to switched off and disconnected device. I repeat- DISCONNECTED. I damaged few laser diodes due to ground loop effect. The voltage between switched off laser power supply and ground soldering iron was high enough to damage laser diode.

Set current to min, switch power supply. Increase current. At first, laser diode is only glow. It is simple LED emitting effects. Optically burn out laser diodes can emit LED light. Increase the current and in some moment, laser diode start to shine very bright- it means that laser generation started. Now you can increase the current up to mentioned in datasheet. Or just try to find max current by your self. High current kills diode, so be careful. Especially when testing burning and ignition experiments*.

IR laser from CDRW device is powerful too. It can withstand 200…300mA current, but “working” current is about 100mA. IR laser beam is invisible and if you use digital camera to watch IR light, be careful. You can burn out not only your eyes, but digital sensor too.

Do not forget to use heat sink on lasers. In max power mode even quite big heat sink become hot.

Also, don’t forget laser safety… (image from www.electricstuff.co.uk – BTW nice web page)

*more experiment will be translated in near future. Take a peek to Lithuanian blog.

I’ve made some improvements to my laser PSU. I added voltage regulator, max voltage on open laser suppressor, spike suppressor. Also some useless improvements…

I didn’t made new PCB, I tested modifications on old board. But all modifications I entered into Eagle software and traced PCB.
I think this “theoretical” PCB is good.

Main difference from old version: IC2- 5V voltage regulator, C4 capacitor, R11 resistor. Capacitor C2 must be very small. It is used to prevent high frequency oscillations. If the capacity is too big, it will shunt input of amplifier and the inrush current through the laser will be very big. PIN2 theoretically is connected to photo-diode build in laser. But all new high power lasers don’t have photo diodes. So this pin typically is left unconnected. So, the resistor value is unknown. D1…D3 are fast schottky diodes. They prevent from reverse voltage during various experiments and connections. One of them is useless.

Laser diode body is connected to regulated supply, so take care that heat sink and laser body is not connected to ground plane. If it is connected, your laser is dead. It is possible to build PSU with grounded body, but I don’t have p-channel power mosfet in my stock. Laser diodes are static sensitive devices- handling precautions required. I damaged few diodes by simple ground loop- my solder iron is grounded and laser was powered from some wall adapter. Ground loop killed diode. Disconnect laser PSU from main while connecting/soldering laser diode.

Use the link and make your own PCB using UV of hot-iron and laser printer method.

PCB image (600dpi).

Here is experimental board (version 1 with modifications):

I improved my laser PSU design: added voltage regulator, additional schottky diodes, some capacitors and it seams that laser supply is quite stable. I tested it with low power led lasers and several high power IR lasers from CDRW devices. Heat sink on the PCB is not mandatory. Only in rare cases, when powered from 12V and using extra power to diode, PCB is hot. As I changed some resistors, the current range is smaller. I decided, that I will not try to pump extra power from these small lasers. Now the range is from 0 to 200mA.

There is two lenses in the photo near PSU. I removed these lenses from photocopier. One lens have build in IR filter, other lens is made from clear optical glass. The bluish color of filtering lens is from copper ions in the glass.

And now, small experiment about wavelength filtering. Take note, that IR laser is much more powerful than RED. Red laser in this experiment is from cheap DVD player.

As we can see, special lenses filter IR light quite efficiently. Similar IR filters are placed inside all digital cameras. Sometimes it is possible to remove this IR filter and get very weird IR camera. The problem in modern USB web cams is, that IR filter is build in camera’s lenses and it is impossible to remove it. The RED beam cross both glass lenses without any visible problem. (Color change of the photo is due to white balance- digital camera set bluish color as white base).
The current through the diodes in both case was about 40mA (IR laser is in low power mode, for “reading”).

Small movie: IR laser. 100mA. From CDRW. Unfocused. (xvid, 1.5Mb)

My red laser stock was empty. Mainly due to my errors and experiments. As I didn’t find spare DVD recorders, I switched to infrared lasers (IR). It is much easier to find powerful IR laser- the source is any CDROM recorder. In newer high speed CDRW devices, lasers are quite powerful.

IR laser beam is invisible. Sometimes you can see so red light emitting from laser diode (do not stare to focused beam). It is not a miracle- you can’t see these wavelengths. It is just secondary LED emission near the cavity of the laser. Even if the laser part of the device is burn out, you can see this reddish light. Laser emission is very interesting phenomena- when we increase the current through the diode, we get LED light. As we increase current, suddenly optical generation starts – laser process is on. All low power and old lasers have photo-diode to detect this process and to measure optical power. New high power laser modules do not have photo-diodes installed, even the laser is in 3 pin package. You can notice, that third pin is not soldered to PCB. And if you disassemble laser itself, you can see, that there is not wire connected to this pin. Neither you can find photo diode. I wanted to get modern driver chip datasheets from elentec-intersil, but I received answer, that these documents are not for wide publication. Why? I don’t know. These chips are in every modern DVDRW device… So I can’t find how laser power is regulated in these devices.

I improved my power supply and started tests with lasers. Did I mentioned not to power high power laser diodes without coolers? So don’t.

To detect IR beam use any digital camera, USB camera or any other consumer device with CCD camera. CCD cameras’ have IR filter, but it is to weak to block laser beam.

This nice photo is made when I placed my digital camera lens to CDR recorder optics. As optics is untouched, we can see nice interference pattern. Just cool photo.