The Tunablue - wavelength tunable blue laser

[Cyparagon]

The communication problem here is the subjectivity of the word "broad". How about rewording that to "broader," yes? Lasing (by common mechanisms) selects a very narrow bandwidth. If the device is emitting light, but not lasing, it is also almost by definition going to be broader.

 

[Atomicrox]

My new 505nm and 480nm diodes also have the broad emission before lasing.

 

[Benm]

Well, since you have made the statement that ALL laser diodes do this, I'll be watching very carefully to see if I can indeed find a definitive answer to this question. I know I have seen diodes that, at the moment any light is available, lase and don't have a broad spectrum of light. I will be extra vigilant from now on.

Well, you may find some rare exception to the rule, though i really doubt it.

Some may have a -very- narrow range between outputting visible light and lasing, but i bet that gap will always be there. No matter what diode you come up with, i'm quite conviced it will have a state in which it emits light on a broad spectrum (even if it's just a few photons per second) before it starts lasing.

And you could also discuss what 'lasing' actually means. To me it's the point where the output light is coherent, even if the coherence length is small (but at least larger than the laser cavity length).

Most diodes do not have a significant range in which there could be doubt about it though - if you increase the current gradually you'll see a sudden jump between a led-like emission and a laser beam coming out. If you want anything on the border of that you'd need to set a pretty precise current at a given temperature to get it sort of 'halve lasing'... that will not happen by accident or coincidence, but if you purposely aim for it, it is possible.

 

[paul1598419]

It would appear that some diode's line width is broader than others before reaching the lasing threshold. Others do not. I suppose it depends on the type and way they are mass produced. It shouldn't be assumed that all diodes do this as it isn't a physical property that all LDs have. The line width can remain fairly narrow while emitting light before lasing. I have been trying to narrow down how to predict which will and those that don't, but still have more research left to do.