Multiple wavelength emmision

[Grix]

Got this from PL.

Grab a 445nm diode and power it up so it barely glows, then shine it through a diffraction grating. What do you see?

 

[Ash]

Whoa. Green and Violet with the blue? :wtf:

 

[Meatball]

Ah, but did we yet determine if it is lasing or not? Making semiconductors emit light spontaneously is very difficult.

 

[Canuke]

Don't you get yellow from 405nm's this way? I"ve never tried, but I've seen many references to that here and there.

In this case, it's an LED below lasing, so the output band is going to be fatter.

 

[Benm]

Its a wellknown phenomenon with leds. Laser diodes arent likely to behave much different, but this all happens -below- the lasing treshold.

The cause lies in semiconductor impurity. This causes small areas of the active area to have different bandgaps from the bulk of the diode, and those produce some light when driven at a voltage below the treshold for the bulk.

These emissions are still present when driving the diode at full current, but are then overwhelmed by the bulk color. No population inversion is achieved though, so they are pretty much useless for laser construction. Compare it to the difference in a HeNe laser between its output color and what the gas mixture emits: The emission is fairly broad, but only a few wavelengths can lase in those tubes.

 

[Cyparagon]

Most lasers have LOTS of wavelengths that don't lase. Here's the Helium Neon spectrum, and only ONE exits the tube through the OC:

 

[Bluefan]

And the 632.8nm line isn't even the brightest, yet is has the highest gain.

 

[HIMNL9]

This is why different color lasers exists, from He-Ne tubes

Anyway, He-Ne tubes lases from some different things, not just the plasma discharge in the capillar tube ..... the "dominant" wavelenght that they emits is due from the plasma, but also from the angle of the brewster window (2 of them, in external mirrors setups, usually only one, in small sealed units), from the thickness of the dielectric layers that compose the reflective surface of the mirrors (that usually have the thickness of the layers matched with the wavelenght, for improve "constructive resonance" reflection), and for the more professional units, from the lenght of the resonant cavity (but cheap tubes don't care too much about this)

I remember from long times ago, i had seen an article about a lab unit ("small" as a big desk, LOL), that had variable elements in the cavity, and was able to produce almost all the lines of that spectrum, also if with different powers ..... it was defined a "variable wavelenght unit" ..... they was costing "only" 22.000 or 23.000 $

 

[LSRFAQ]

I remember from long times ago, i had seen an article about a lab unit ("small" as a big desk, LOL), that had variable elements in the cavity, and was able to produce almost all the lines of that spectrum, also if with different powers ..... it was defined a "variable wavelenght unit" ..... they was costing "only" 22.000 or 23.000 $ [/QUOTE]

You need to buy it from the factory instead of a catalog that resells it. The Research Electro Optics tunable is only ~7K new. I've tuned one from green through orange via yellow and red. Its really a downer when you get your hands on one, low power on the "fun" lines, and the adjustments are touchy as hell. I have no doubt a pile of them have been thrown out as dead from loosing lasing as the prism moves between lines. Its really just the size of a kids lunch box. Still cheaper then buying 5 other tem00 lasers thought. Where it really shines is the beam quality is phenomenal, even if the power is not.

REO Precision Optical Solutions

Steve

 

[LSRFAQ]

I remember from long times ago, i had seen an article about a lab unit ("small" as a big desk, LOL), that had variable elements in the cavity, and was able to produce almost all the lines of that spectrum, also if with different powers ..... it was defined a "variable wavelenght unit" ..... they was costing "only" 22.000 or 23.000 $ [/QUOTE]

You need to buy it from the factory instead of a catalog that resells it. The Research Electro Optics tunable is only ~7K new. I've tuned one from green through orange via yellow and red. I was a guest in a government lab that bought one, and they were very happy with it.

Its really a downer when you get your hands on one, low power on the "fun" lines, and the adjustments are touchy as hell. I have no doubt a pile of them have been thrown out as dead from loosing lasing as the prism moves between lines. If you hurry, you'll miss the gain "sweet spot". Its really just the size of a kids toy tool box.

Still much cheaper then buying 5 other tem00 lasers thought. Where it really shines is the beam quality is phenomenal, even if the power is not.

REO Precision Optical Solutions

Steve

 

[JLSE]

This was a pic I took approx 1 1/2 yrs ago. It was a PHR 405nm LD
that had blown but still emitted light. The pic was taken aprox 15ft
from the LED'd laser with the collimator still attached..