Is my green laser "near TEM00" or TEM10

Hodad · Sep 10, 2008

I was trying to measuring the beam diameter of a 532nm DPSS laser and I noticed that the beam was more oval shaped than round. I guess no beam is perfectly round but this one looked borderline TEM10.

I'm having to view the spot through a digital camera (I have ML7 safety glasses on order from a recent GB but they won't be here for a while). The spot faintly resembled the attached image from a gaussian chart . I can't tell for sure though as the brightness of the spot was making it hard for the camera to focus, etc. If I can ever get the settings right I'll post an actual photo.

Is there any other (or better) way to determine what mode beam I have?

darklandz · Sep 10, 2008

shine your laser through a magnifying glass or any focusing lens and if the projected dot matches that of the image, its running in TEM01 mode.

daguin · Sep 10, 2008

Hodad said:
I was trying to measuring the beam diameter of a 532nm DPSS laser and I noticed that the beam was more oval shaped than round. I guess no beam is perfectly round but this one looked borderline TEM10.

I'm having to view the spot through a digital camera (I have ML7 safety glasses on order from a recent GB but they won't be here for a while). The spot faintly resembled the attached image from a gaussian chart . I can't tell for sure though as the brightness of the spot was making it hard for the camera to focus, etc. If I can ever get the settings right I'll post an actual photo.

Is there any other (or better) way to determine what mode beam I have?

Shine it through a magnifying glass onto a fairly close , flat surface.

Peace,
dave

[highlight]**EDIT**[/highlight] Ditto

Hodad · Sep 11, 2008

Thanks, I'll try that tomorrow. I'm getting to tired to be safe tonight.

I just read some "heavy" ;D material from Melles Griot about "Real Beam Propagation" :

and now I'm more confused than ever.

All I halfway understood was this:

"The need for a figure of merit for laser beams that can be used to determine the propagation characteristics of the beam has long been recognized. Specifying the mode is inadequate, because, for example, the output of a laser can contain up to 50% higher order modes and still be considered TEM00."

Apparently, it goes on to suggest, the M[sup]2[/sup] is a better figure of merit to determine the qualities of a laser beam.

But I thought M[sup]2[/sup] was just a measure of how round the beam was.....

The specs say this laser is supposed to be "near TEM00" and M[sup]2[/sup] : <=2.0. But in light of the quote above. What does that mean?

All I really want to know is do I have a good beam or a not so good beam? Is it single mode (one beam?) or multi-mode (more than one beam?)

Just when I thought I had a grip on understanding it

Sorry, I'm just expressing my frustration at not being able to make sense of it.

Hodad · Sep 12, 2008

Here are the pics I took of the beam spot with and without the suggested magnifying glass.

I posted multiple pics to show any change in the beam. They were taken over a 5-10 minute period. Does anyone see anything other than "near TEMoo" ?

This one is with magnifying glass

Hodad · Sep 12, 2008

and another

FrothyChimp · Sep 12, 2008

That's near TEM00. Near TEM00 means the Gaussian curve expected in a single transverse mode is clipped across the top in some manner. It could be level, have a small dip in it or angled.

Hodad · Sep 12, 2008

and another

Hodad · Sep 12, 2008

and the last one with magnifying glass. This is the one I thought the beam might be starting to "split" in.
i'm looking at the brighest part in the center, notice how it seems to have a dip in it.

Maybe thats what you are talking about FC. Or have you seen this one yet?

Hodad · Sep 12, 2008

this is without magnifying glass

Hodad · Sep 12, 2008

and the last one, (no magnifying glass).

Sorry I didn't get them all up until now. I thought I could post multiple images in one but I guess not.

Hodad · Sep 12, 2008

Here's an image of the spot on thermal paper. This was done right in front of the aperture. looks like TEM01*
on the Laguerre-gaussian chart.

Hodad · Sep 14, 2008

I guess this thread may be dead

I guess my thread is old.

daguin · Sep 14, 2008

Re: I guess this thread may be dead

Hodad said:
I guess my thread is old.

You received the answer from FrothyChimp

Peace,
dave

Hodad · Sep 14, 2008

Re: I guess this thread may be dead

daguin said:
[quote author=Hodad link=1221084038/0#12 date=1221380854]I guess my thread is old.

You received the answer from FrothyChimp

Peace,
dave[/quote]

I know, and I was very happy about his confirmation that it was near TEM00. He has answered many of my questions and been of tremendous help to me. But I had not posted the latest image until after he responded with the answer.

BTW -thanks again FrothyChimp. You always come through!

Is my green laser "near TEM00" or TEM10

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