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445nm Direct Injected Laser Diode


This webpage is about the recent developments relating to 445nm laser diodes found in new DLP projectors.
Disclaimer:
* All of this information is provided as 'best effort' by myself, and I cannot guarantee any of these measurements.
* These diodes are class IV lasers, and must be used with extreme care. Under NO circumstances should they be incorporated into a hand-held laser pointer, unless correct measures have been taken to reduce the output power to <5mw (putting a safety interlock on a laser pointer does not make it safe nor legal!).

Specs

At aproximately 30C I took the flowing spectrum of the output, the multimode (longitudinal modes) characteristics of the diodes can clearly be seen as the power being divided into 2 large modes and several smaller ones. The current for this test was 300ma, well above the threshold current for the diode. The wavelength of this (and all laser diodes) shifts with varying temperature and current, shifting to longer wavelengths with increasing temperature/current. That said, at 30C the diode I tested was actually 442nm. All of my spectrometers are currently in the wrong county so I cannot take any further measurements to comment on the wavelength spread across different diodes or variation with temperature.

In Projector Testing

Before removing these diodes from the projector, I added a 1 ohm current sense resistor in series with one of the diodes. I then measured the voltage across it with an oscilloscope, and used ohms law to deduce the current through the diode (1V across the sense resistor equals 1A of current through the diode) so the trace below shows the diode current at 500mA/division:

NOTE1-I this trace is inverted (ie, the diode shows negative current because I had the clipped the probe in backwards).
NOTE2-I am not sure if my projector was in economy mode while this test was taken, if it was then the power may be slightly higher than what I measured. I am currently trying to find someone with a projector and oscilloscope to confirm. From the above data it can be seen that the diode is being run at 1.44A for 3.2ms, 1.22A for 1.3ms, and is run at approximately 20ma the rest of the time (this current was too small to accurately measure with my equipment, it is in the range of 5-50mA). I measured the average power from the projector to be 0.88W (per diode). I then tried to go back and figure out what the powers were at the 1.44A and 1.22A currents, by assuming that the output power scales linearly with current past the threshold current -ie, if plotted in a line, power = (current-200mA)*arbitrary constant. From this I concluded that at 1.44A there is 1.7W of output power, and at 1.22A there is 1.4W of power, which match within 10% of th CW measurements I took.

More Information

I can be contacted at contact@krazerlasers.com

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