Archive for April, 2009

Prototyping.. updated

April 24, 2009

Well the last few weeks were quite productive and not only I completed a series of measurements, but I also finalized the development of a stable laser diode driver and TEC controller. All went very smooth without major obstacles, apart from a surprise with trim pot noise.

I now have received the PCBs for the drivers, and in an evenings’ work eagerly completed the first prototype:

Next thing is to check that all still works properly and conduct extensive measurements. If all goes well, I would be able to produce 4-5 complete units plus a few drivers separately, and put them up for sale. Please contact me if you are interested.

Open can and blu-ray DVD diodes…

April 4, 2009

I have acquired some more laser diodes for testing their suitability for holography.

The first thing to try out was to measure the mode spectrum of one of those high power “open can” DVD burner diodes, which can do several hundered milliwatts when tortured. Well, the news is –not unexpected– that those diodes are totally unsuitable for holography. see here. Moreover I found the the familiar Sony SLD1236VL and SLD1239JL-54 diodes a little bit better, but not too much.

Summarizing, for all DVD diodes I tested the rule seems to be that they can run single mode at up to 70-90mA, which yields approx 20-30mW. There may be exceptional stable spots higher up, eg. I got approx 50mW with one Rohm diode, for example. The best diode so far was the Mitsubishi ML101J27 which got up to approx 80mW (with some weak other modes; true single mode up to approx 50 mW). Thorlabs sells it as single mode diode, probably for good reason, however there is no mention of this in the data sheet.

There is a number of declared single longitudinal mode diodes, esp from Opnext/Hitachi, some with powers exceeding 100mW. Most likely they would be the way to go, I will try to get a handle on them and do some measurements; unfortunately the more powerful ones are quite pricey. But it seems there is no easy way around that if one aims for more than 30-50mW.

Note added: I now checked a GH04P21A2GE/PHR-803T “blu-ray” diode and the results are here. In a nutshell: totally unsuitable for holopgrapy!