WTB: Driver for Coherent 488-20 OPSL

[rhd]

Just purchased an unknown-state OPSL head, and I need a way to drive it. The only driver that looks even potentially capable of driving it on eBay is not available to Canadian eBay members (hate that).

Anyone have anything appropriate on hand?

 

[Bluefan]

You got that $200 ebay auction? If that auction appeared a month ago I'd go for it, but unfortunately I couldn't afford it when it appeared. This may be very useful to you:
W's laser heads and precision drivers for laser diode holography

 

[rhd]

You got that $200 ebay auction? If that auction appeared a month ago I'd go for it, but unfortunately I couldn't afford it when it appeared. This may be very useful to you:
W's laser heads and precision drivers for laser diode holography

I sure did

Since I don't know the state of the unit, I haven't been crazy about the idea of spending $150 on the driver.

That page you linked me is a god-send, because it gives the pinout of the connector (sort of).

Screw buying a driver, at least not up front. I'm going to build one

At first, I'll just monitor the LD thermistor with a DMM, drive the TEC with a small variable PSU reacting manually to temp changes, and then drive the LD from a bench PSU. I'll only need to do this ^ long enough to verify that it works.

If it does, I'll see about talking to someone smarter than me on the forum about building a TEC driver that respond to the LD termistor. The rest, should be simple.

 

[Super Critical]

Let me know how it goes. I'm thinking of getting one of those things. There are sevral on ebay. It just needs a PS and Heatsink and TEC, which may prove slightly difficult.
COHERENT SAPPHIRE 488-20 LASER #2 | eBay

 

[rhd]

So, to answer the big question:

- YES, you can just "dumb drive" (IE, hook up to a basic constant-current bench PSU) a Coherent Sapphire, at least for a few minutes.
- YES, you can do it heatsink-less, at least for a few minutes.

If you think logically about both issues, it's mostly a heat issue. The LD is pulling in about 1.8A x 2.2V = ~4W. It's putting a negligible < 20mW of light out the front. So you're basically dealing with 4W of heat generation.

It's that 4W of heat that basically all of the driver electronics are intended to deal with. It's why you've got an internal TEC to move the heat away from components, and temperature monitoring thermistors, etc.

4W is not a *ton* of heat, but it's also nothing to sneeze at. But chances are that a high powered 532nm portable, or even a moderately powered 589, will use a 2W pump diode, with NO internal TEC or temperature monitoring. Understanding this, it makes sense that you can safely drive a Sapphire for a minute or so before worrying about heat.

Now, long term, what I need to do is find a way to create a small driver that at the very least will run the TEC. That much should be relatively simple. Ideally, I would like it also to respond to the thermistor and at least switch the TEC on and off depending on whether the temperature measured was inside or outside of a particular range.

(If anyone has any ideas, I'd love the help. I don't know how to accomplish that ^ yet. I've got some research / thinking to do).

 

[ZRaffleticket]

Ah so you got it working? (sort of, at least lasing) 488nm is a sight to see! If only these things could be made into portables easily...

One of my buddies is pretty good at designing circuits (he may be able to plan one like that), I'll give him a call when he's off work if you'd like.

 

[rhd]

Ah so you got it working? (sort of, at least lasing) 488nm is a sight to see! If only these things could be made into portables easily...

One of my buddies is pretty good at designing circuits (he may be able to plan one like that), I'll give him a call when he's off work if you'd like.

I did!

I'm sure it only puts out a few mW, but it lases just fine. I got the TECs running, and was able to measure LD and case temp just fine.

And honestly, this thing is so tiny that you could (probably) portability the internals. The only reason I haven't ventured into the shell is that I think it might contain something other than air. Until I know the physical properties of the guts, I don't want to risk there being some sort of exotic crystals inside that will die upon exposure to air.

But really there's not much to driving them. Even the driver I want to create won't be that tough to figure out. I really only need to figure out how to make a switch that will close a circuit when resistance drops to about 12k, and shut off when the resistance rises to around 13k.

 

[Sigurthr]

Very nice RHD!

Simply base bias a NPN transistor so that when the temperature is low the pull up resistance is too high and not enough current flows to the base to allow conduction. A simple pot + thermistor in series between base and Vcc will do. You vary the pot's resistance with the thermistor at just below the minimum on temp so that the transistor stops conducting. When the thermistor gets warmer the base current will increase and the transistor will start to conduct. Of course this assumes you have a thermistor with a resistance that drops with temperature increase, they come in both varieties. It can be made with one that increases resistance with temperature but it isn't as simple to set up.

If power draw by the TEC isn't an issue you could just place the NPN between the TEC driver and the TEC instead of between psu and TEC driver. The TEC would be always on, but the degree of cooling would depend on how warm the device gets. Just remember to counter the Vf of the NPN and select an NPN who's Ic is > than the TEC's intended maximum If.

And to put my money where my mouth is:

I spent a couple hours drawing this up and figuring out what scheme would work best given I have no idea the responce curve of the thermistor or what RHD has access to. If you (not you RHD, anyone else =P ) can do better, please do.