Intro: OEM Laser Diode System
I am a member of the Koch lab at the University of New Mexico. We primarily do single molecule force measurements on DNA and chromatin. To do these experiments, we needed a high power laser that was cheap and reliable. I was able to design and build (with the help of my lab mates) an OEM laser diode system using parts purchased mainly from Thorlabs and Digikey. These are my instructions on how to make our system. You can also find these instructions on the lab's website under our research tab.
The main reason we went with this design is cost. The total laser system is very cost effective for the amount of power one gets with it. But, because it is a research laser, this is not a build for the average do-it-yourselfer. Mainly due to cost. While it is cost effective for a lab, it is not so for an individual. If you are an individual and you want a laser diode system, I'd suggest you looking at the many builds on this site for taking apart a CD/DVD burner.
As a research laser, you are at your own risk for building it. If something breaks because of negligence, consider it a learning experience. If you hurt yourself when you build it, then you shouldn't have started this build. You should also read all the manuals associated with all parts of this build. If you don't, then you may be in for a world of hurt. Now that you are warned properly, enjoy the build and your new research quality laser system!
Of course one of the advantages to using this system is that when a diode burns out, that's all you have to replace. As opposed to commercial laser diode systems which have to be completely overhauled if something goes wrong.
Step 1: Parts List
Below is a list of parts needed for this project. Not included in this list are the tools needed. I will make sure to link to the tools we used for this build in the following steps.
Laser diode & temperature controller
Temperature cooled mount for diode
Cheap 35 mW Diode
Asphere for collimation
Back plane connector
Header crimp connector
Right angle headers
Copper clad proto board
Heat shrink tubing
Step 2: The Enclosure - Front Panel
To ensure proper air cooling and isolation for the laser circuitry, you will need to get a box to house everything in. You will also need to make large holes in the box so, use of a Dremel with a cut off wheel is required.
It's time to cut out the access hole for the display panel. You can use the supplied dimensions diagram, or you can just figure out where the hole should be for yourself. At any rate, cut the hole out with the Dremel using the cut off wheel. When you are done, you now have an access hole for the front panel and a spot to mount the front plate. Don't forget to file the edges down from the cut, or you may cut yourself!
You can make the holes for mounting the front plate to the box, however, you may want to wait until step 5 to do so. We made the holes right after cutting this access hole and we couldn't get the front plate to line up properly. This is why I suggest waiting.
Step 3: The Enclosure - Air Cooling
In order to ensure the circuitry to our system is cooled properly, we opted to force air cooling on it. We cannibalized an old computer for our fan but if you don't have an old computer, just get one from Digikey. If you do purchase one, make sure to get fan guards as well. Also, make sure you get a fan that runs on +12V and uses the smallest amount of amps possible. It's only a recommendation but if you don't, you will have to supply more circuitry later on so your fan will run.
To get proper air flow, you need to make an escape hole, as well as the hole required for the fan. We put the escape hole on top of the system (hot air rises) and the fan hole on one of the sides of our box.
We positioned the fan in the middle of one of the side panels. We taped the fan guard on the box and used a center punch to start the hole needed to be drilled. We then used a hand punch to make the clearance holes. Make sure the hole size you use is proper for your fan screws. The hand punch is a great tool and the only reason why we didn't make all our holes with the hand punch is because some holes were not accessible by the punch. Once the screw holes were made, we then cut out the hole for the fan using the Dremel and the cut off wheel. Deburr!
For the air escape hole, there is no fan. But, the procedure is still the same. Tape the guard on the top of the box (where ever you like), use your center punches to make a centered divot, then use a chuck style pin vise with a drill bit to make the holes. This is a case where the hand punch would have been nice to use, however, it couldn't reach where we wanted the holes. Remember, the holes you make will depend on what size guard you get. What ever size you end up getting, make sure you drill the hole for the proper sized tapped hole and you use sheet metal screws.
Step 4: The Enlosure - Power Connections
The enclosure needs power supplied to it so the circuitry will run. To get power to the box, we mounted 3 panel mount banana connectors to the side opposite the front plate.
To make these holes, determine where you want them on the box and again use the center punches. Using the pin vise with a 5/16" drill, make the holes for the banana connectors. I like to space mine about 1" apart from each other. Deburr!
Step 5: The Enclosure - Circuit Mounting
The brains for the OEM laser diode is the laser diode & temperature controller circuit. To mount it to the box, you will need to remove the 15 pin D-dub connector nuts from it first. Attach 4-40 tapped standoffs 3/8" long on the 4 corners of the circuit and put it in the box.
Now attach the front plate to the box and feed the 15 pin D-sub connector on the circuit through the plate. Reattach the D-sub nuts and tape down the front plate to the box. This is where you will now make the holes to mount the front plate to the box. Also, if you need to remove some material from the display panel access hole, I'd recommend using a nibbler. In a perfect world you won't have to remove material, but let's be realistic here...
Their are 4 holes that mount the front plate to the box and these are where you will use your center punches to center your drilled holes. Once the holes are center punched, remove the front plate and circuit from the box and use a #43 drill bit with the pin vise to finish the holes. I found that using a pin vise was easier than trying to get a drill press to do the job. You should use 4-40 sheet metal screws to fasten the front panel to the box.
Unfortunately, all the parts from Thorlabs are metric. This means that a 4-40 screw will almost fit into the clearance holes of the front plate. They do fit, but they are really snug. Just keep this in mind when you go to mount the front plate. The same applies to the 4-40 standoffs on the circuit board.
The circuit board still needs to be mounted to the box. You can either glue the standoffs to the box or you can try and make holes in the box using your hand punch. We opted to mount the circuit to the box, but in doing so, we screwed up several times with the hole placements. Using the hand punch to make holes that are oversized is a great idea, just use washers when you screw things in.
In retrospect, I'd go with gluing. It's faster and easier. If you go this route, make sure your glue rocks otherwise your circuit will fall and fail. (The main reason why I didn't want to do this in the first place.)
Step 6: The Display Panel
The display panel can be mounted to the box now. To do so, you will need to remove the switch from the circuit. Make sure that when you remove the switch, you do not remove the switch's stop.
In our first attempt to make this laser, we unfortunately did remove the stop. I tried to get Thorlabs to tell us where the stop should go but instead of telling me, they asked for me to return it for an exchange. Well, if you do remove the stop, it should be in position 6.
Attach the ribbon cable to the main board and thread the switch through the front plate. You will notice that the display panel will not fit snug to the front plate. This is because there is a guide rod on the switch that doesn't quite fit into the guide hole on the front plate. It doesn't matter because you will ultimately be tightening the nut on the switch you removed earlier to keep the display panel in one place.
Step 7: On/Off Circuitry - the Board
Since this is an OEM system, you need to supply on/off circuitry. Theoretically you could use wires to jump between every connection but I thought that using a break away board would be better.
I'm not about to describe how to make a circuit board. You can find out how to make one on this website. What I will do is post my diagram, the completed circuit, and a pdf of the circuit for you to print.
The basic idea of the circuit is to supply an on signal to a pin on the main board for both the temperature controller and the laser diode. Including LEDs and switches, helps a user recognize that the system is on.
To mount the circuit board to the box, I again used my hand punch. Except this time I had the idea of using wax to mark where the holes needed to be. By pressing the board into the wax, I got an indentation of where the standoffs were and made a hole. It works nicely.
At this time, I also made the holes necessary for our panel mount LEDs and switches.
Step 8: On/Off Circuitry - the Wires
In step 7, you saw an image of our break away board populated with wires. Here, I'll briefly describe how to make them. I made the executive decision to use header connectors since I've used them before and I can make the wires for them quickly. (I also had spare parts for them).
Since a picture is worth a thousand words, I'll let my diagrams describe how to make these wires. One end has a header connector and the other end has a pin from the required back plane connector.
Remember that the LEDs and the switches are going to need header connector wires made as well. Also, you will need to solder wires from the banana connectors to the break away board and the back plane. Don't forget to supply power to the fan as well.
Step 9: Final Assembly
Once you have modified the box to house the circuitry, assembled the break away circuit, made the wires, and connected them, you are ready to supply power to the system. To supply power, we bought an OEM power supply from Mouser. All we did to the unit was to add a fuse, add a switch, add banana connectors, and enclose the PS.
Plugging in the power supply to the box and turning it on supplies power to the control circuitry. Now you are able to attach the communication cable to the temperature cooled mount for the diode to the box via the D-sub connectors. If you have a diode, you are up and running. The system will accommodate up to 1W laser diodes in the 9mm or 5.6mm can package.
You should set PID control before using the system. We have not been able to get a good PID control for temperature mainly because none of us has ever used such a control system before. It does work, but it doesn't respond as quickly as we would like it to.
We have a 1W 690nm diode in our system right now. Because temperature control is not optimal, our power stability is not optimal. If anyone knows of a way I can set PID control better, I'd really like to know. Right now we are operating at 60% power because I have 1000mA of current going to the PID temperature control. Any advice would be great!
Step 10: Power Stabilization
It appears that the stability of the diode is pretty bad due to improper temperature stabilization. Right now we have 1.0 Amps going to the temperature controller. We can't supply very much more due to the limit of our power supply (3A output). I'm looking into getting a different power supply so we can supply more power to the temperature control. If this works, then I will update a new file showing the temperature stability of the system.
In both cases, the power output dropped as the temperature increased.