TEM00 to TEM01 Mode Hopping 532nm

[Alaskan]

What causes an otherwise TEM00 laser to mode hop to TEM01? I mean, other than temperature changes? I have several of these lasers, identical, only one does this.

Here's a short video showing it:

http://photos.imageevent.com/qdf_fi...ations/irledandlaserproject/TEM Splitting.mp4

 

[VisibleGreen]

Dis-alignment I believe or damage to the diode

 

[Alaskan]

I'm showing it with the lens off on a wall about 12 feet from me. This is the output after expansion through a double concave lens.

 

[lazeristasUVISIR]

+
A wrong current of the pumping laser diode. Can you change the current and observe the beam?

Is this a sandwich crystal type laser?

 

[crazyspaz]

crystal temperature mainly as well as pump temperature- only if said pump temperature shifts the output by x amount of nm.

 

[Alaskan]

Thanks everyone, late to see the responses.

 

[o_DEATH_ANG3L_o]

Do you have an oscilloscope?

 

[Alaskan]

Yep, 100 MHz.

 

[o_DEATH_ANG3L_o]

I was going to suggest connecting your driver to your scope and see what you get whilst adjusting the current. Some factors that can affect whether or not mode hopping occurs are laser case temperature, injection current and optical feedback. Reflections of the laser beam back into the laser cavity should be avoided. Slight canting of any partially or completely reflective surface will help eliminate feedback.

 

[Alaskan]

Thanks, I've noticed temperature does impact whether this happens or not quite a bit for most of my cheap lasers which do this, but this one particular laser seems to be stably unstable regardless. I find it an interesting effect.

 

[o_DEATH_ANG3L_o]

Do you happen to have a small TEC module handy? If you don't then I would pick some up. these little things are amazing. If you do then cool that diode down. Run 12v through the TEC and see if your laser still goes TEM01. If it does, blame the optics lol. :crackup:

 

[Alaskan]

Do I have TEC's? LOL... man, I have a bunch of them, like 50+ of them of many sizes. Thanks, might be easier just to spray the body of the host with some component cooling spray, as long as I don't cause it to get too cold and condensation becomes a problem. Even easier, I can set it outside for a few minutes, it's getting chilly here now.