690nm LD + flickering beam

On: Sun, Jan 27, 02 06:00:02 AM

Thilo K. wrote:

RESPONSES

Tom B. - Sun, Jan 27, 02 07:26:02 AM

You will not get the change in wavelength that you want by changing the driver. Wavelength changes by only a few nm with drive current, and is mostly determined by the LD construction. You want a new LD and driver, and there are MANY low-cost LDs and modules available in the 640-660 nm range. For German sources, try http://www.roithner.de/ regards, tom 24.67.253.203

Thilo K. - Mon, Jan 28, 02 09:09:50 AM

why do all people think that Roithner would be a good choice ? Please, do not recommend roithner any more ! I do not tell you because I could be a competitor. I claim that because I ordered drivers there, and none worked the way it should. So I sent all drivers back and told them to repair. But there was no response at all - though the address the delivery was sent to was rightly written. So I lost very much german marks. So please, ask as much people as you know not to order at roithner. 145.254.228.6

Tom Naiser - Mon, Jan 28, 02 02:29:33 PM

I have recently bought an iC-WK laser diode driver chip from lasercomponents (www.lasercomponents.de). You can either get the SMD-chip alone ( 6 or 7 Euro) and and build the driver circuit by yourself (very easy - see the specification file available from lasercomponents - you only need a handfull of resistors and capacitors) or you can buy the readybuilt driver-module (which allows diode power adjustment) iCSYWK1D (or iCSYWK2D if you have a p-type diode) which costs around 15 Euro. The driver works fine - the fringes are rocksteady (at least over a time range of about 10 Minutes). A problem that I still have using this driver with my 35 mW Mitsubishi-diode is that of the "sliced bread-syndrome" described elsewhere (the problem is probably caused by the diode itself and not by the driver). As Tom B. said, varying the diode current can change the wavelength only by a few nm. Has anybody experienced that the the "sliced-bread-syndrome" gets reduced by increasing the diode current. I have read that if the laser power is increased the mode in the centre of the amplification profile is growing stronger than the modes adjacent to it. So the single mode property of a diode, that we all want, should improve as the diode current is increased. 132.180.20.81

Tom B. - Tue, Jan 29, 02 03:55:12 AM

Re sliced bread: A while ago, I mentioned looking at fringes from an ML1016 in an simple interferometer setup. I noticed that as I varied the mirror spacing, the fringes would vary from high contrast to low contrast evey inch or so of spacing. I guessed that this was due to multiple lines in the spectrum. One big unknown is whether reflections back into the diode from the interferometer setup were destabilizing it. When I set the mirrors to a low contrast spacing and reduced the drive current from 25 to 15 mW, the fringe contrast seemed to improve, but was never as good as the best contrast position. There were a couple of "zones of instability" in the 15-25 mW range in which fringes were completely washed out. Listening to the amplified photodiode output, these fringe washouts were accompanied by lots of noise, which I assume was due to frantic mode hopping. One thing I did not try, and will have to try soon, is to look at ML1016 behaviour in the 25-35 mW range - maybe it DOES gets better at higher current. 24.67.253.203

Thilo - Tue, Jan 29, 02 06:52:45 AM

Tom N., you mentioned: "[...]and build the driver circuit by yourself (very easy - see the specification file available from lasercomponents - you only need a handfull of resistors and capacitors)[...]" Occasionally, I have already bought the driver ic. Though it might be simple for advanced users, I prefer having a simple tutorial for it - could you describe what to do using simple words ? 145.254.233.238

Thilo - Tue, Jan 29, 02 06:52:56 AM

Jonathan - Tue, Jan 29, 02 01:40:52 PM

Tom B., it's interesting what you've found in regard to mirror spacing with your interferometer. When I've set one up I've encountered similar periods of high and low contrast, as well as complete wash-outs but I've never played around with the mirror spacing. Always attributed the fringe behaviour to temperature fluctuations within the diode. In pursuit of a solution I've talked to various people, and learned that there are various approaches to frequency stabilization of these laser diodes, some already implemented successfully such as Yves Gentet's Samourai laser. Others have only been worked out on paper. One firm that specializes in TEC's and the like has used a software algorithm and control system that basically optimizes the relationship between temperature, power, current, and mode hop zones. It works well with DPSS lasers and they say it can be scaled down for certain diode lasers to eliminate mode hopping altogether. I'm sure there's an inexpensive and practical solution out there somewhere, or at least coming soon. I hope so because I would like to get on with doing holography. There are enough challenges without worrying about the laser. Tom, if you are interested in exchanging some details please feel free to email me at holosjmh@primus.ca 209.90.160.49

Jim McPherson - Thu, Jan 31, 02 11:37:40 PM

Do you think there might be some conflict with the TEC trying to keep the laser lasing the same and the photodiode trying to keep the laser lasing the same? It seems that APC is best when passive heat control is used and TEC's are best when a constant current driver is used. This makes sense if you think about it. If you keep the temperature exactly the same then your current should stay exactly the same, thus making a stable diode.... what do you think? 68.49.37.119

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