I am driving this diode
\http://www.thorlabs.com/thorproduct.cfm?partnumber=DL5032-001
with 10 us long current pulses above its max CW current value, rep. rate 100 Hz. Up to 2.1 times the max current, the optical power increases, and then it begins to decrease. If I reduce the current again, the power restores. Cooling is by air. The emitting element is a slab of some grey material with 2 electrodes attached to it.
Why does this happen?
Elena,
I suspect that you're driving the junction to a temperature where the efficiency drops - keep driving it harder and the optical power may go to zero (and then the magic smoke may come out).
If you can cool the diode more vigorously, you may find that higher powers are possible (without releasing the smoke).
I have no direct answer right now. But because the laser is a device with extremely large nonlinearity the following scenario might be relevant: A high current leads to the generation and injection of charge carriers which consequntly leads to a kind of saturation while the life time decreases rapidly. This would give rise to a decreasing power output. I am sure that the kinetic equations will provide the same result numerically.
I have no direct answer right now. But because the laser is a device with extremely large nonlinearity the following scenario might be relevant: A high current leads to the generation and injection of charge carriers which consequntly leads to a kind of saturation while the life time decreases rapidly. This would give rise to a decreasing power output. I am sure that the kinetic equations will provide the same result numerically.
Yes, my first thought was do make a good heat sink for the diode and see what happens. I think a passive sink + some thermo paste is enough as the emitting element is tiny.
Dieter, your input is interesting. I will try to find more material on this.
Elena,
I would make it a habit to heatsink anything that has runaway thermal characteristics. Laser diodes, as Dieter points out, have notoriously positive feedback coefficients - nice ones will have a thermistor on the die to limit the current. Bad ones wont - and then the expensive smoke comes out.
The diode may be small, but all the more reason to cool it. 1W being dissipated from a die 2mm x 2mm can easily lead to high temperatures in the junction.
A bit of scrap copper or aluminium, some thermal paste, and your problem may well go away.
i think the main cause of decreasing is due to the saturation level and went to the breakdown stage which causes to the decreasing in the power and as for the cooling system may be you can try the TEC controller for the effective use and see the effect of temperature on the power.
I think you have to take into account the time constants für heating and cooling. In the case discussed here you have 10 µs pulses (?) and a repetition rate of 100 Hz. This would finally lead to a more constant temperature over time of observation, i. e. in other words the temperature will not change on the time scale given? Hence electronic as well as optical properties would be more important for the experimental observations.
There are some reasons for it: saturation, nonlinearities, and, first of all, heating.
Read, please, some articles:
V.P. Gribkovskii et al. The Internal Parameters of Injection Lasers. phys. stat. sol. (a) 3, 353 (1970);
V.P. Gribkovskii et al. Trapped Radiation in Injection Lasers. IEEE J. Quantum Electron., Vol. QE-12, No. 6, June 1976;
А.I. Воiкасhеv et al., Some Features of Power-Current Characteristics of Heterojunction Lasers with a Stripe Contact. Quantum Electron. (Квант. электрон.). 1979, Vol. 6, No. 5, P. 972–978 (in Russian);
V.K. Kononenko, B.F. Kuntsevich. Selection of the lasing frequency and heating the quantum-well heterostructure laser diodes. LFNM*2011 llth Int. Conf. Laser & Fiber-Opt. Networks Model., Sept., Kharkov.
Elena, answer on your question please see in specification on your laser. At different temperatures you have different linear power/current characteristics.
Better to perform the cooling of your laser and it's temperature stabilisation.
Elena, Due to Joule heat generation under excess drive current over heat dessipation ability, junction temperature of the laser diode is raised to cosiderably higher than room temperature, which will shrink the band gap energy, resultig longer wavelength shift, typically 0.6nm/K. Another effet is increase in the threshold current as result of reduced gain at higher junction temperatre. So, phenomenon you have observed is linked to latter. Shigeo
I have the same problem with 650nm laser diode driven by CC circuit , when current is increased by 30% of max current, the light power decreased rapidly
Hi,
I also faced the same problem but, after using an appropriate heat sink, this problem gets solved. I would say, try to characterize your current source and make sure how much current is actually flowing through it (which will be an input for your laser diode). Make sure that, the driving current matches with the characteristic curve of your laser diode.
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