curious beam shape on CNI GLP-447

[anuran]

I recently bought a blue 447 nm 5mw laser pointer and was very surprised by the beam shape, I realize laser diodes are supposed to have a rectangular shape,but this seems extreme. I wondered if anyone could tell me if this is normal for this type of laser? All of my previous ones have been dpss type.
Here's a picture of the beam hitting a CCD at ~5 inches away, attenuated by a polarizer.

BTW the beam is 4.00 mm wide.

 

[rpaloalto]

Yes this is normal, the 445 diode is a multi mode diode.

 

[Meatball]

at 5mw, I'm surprised that it is even lasing. It looks like of the middle (or largest) of the emitter localizations is lasing in your case, which is just fine really.

It doesn't look entirely centered however...

 

[anuran]

Yes this is normal, the 445 diode is a multi mode diode.

Thanks. I was afraid of that.

at 5mw, I'm surprised that it is even lasing.

Yeah, actually, it seems to overheat and produce a uniform dim blue light if I leave it on too long. It pulls about 240mA at 5 V. The beam does seem to be very close to the spec.ed 5mW, its brightness appears about the same as a 5mW DPSS 473nm that I had measured a while back.

 

[ped]

Thanks. I was afraid of that.

Nothing to be afraid of, perfectly normal and fine for what we use it for.

Yeah, actually, it seems to overheat and produce a uniform dim blue light if I leave it on too long. It pulls about 240mA at 5 V. The beam does seem to be very close to the spec.ed 5mW, its brightness appears about the same as a 5mW DPSS 473nm that I had measured a while back.

It should be drawing more than that at 5v , i think somethigns wrong there. See graph below

 

[anuran]

It should be drawing more than that at 5v , i think somethigns wrong there. See graph below

Actually, looking at your chart, I'd say 5mW @ 240mA is about right. The setup is current limited, so probably the full 5V is not getting through.

 

[RA_pierce]

The dimming issue is probably "normal," too.
Some have reported that as the diode warms up the threshold current increases.

 

[anuran]

Ah. That would explain it.

I really had wanted a 5mW gaussian beam :sigh:. I guess I'll try cranking it up to 500mA ish and put a spatial filter on it

 

[Justin]

For a 5 mW gaussian beam in blue you will need to get a 473 nm DPSS laser. I don't know of any other easily attainable wavelength that will do this, and even these 473s tend to drift into TEM01 or worse from time-to-time, depending on the build quality and ambient temperature. The 447 nm diodes are certainly not like this, and if you're looking for good beam quality and you don't need tons of power then they may not be the best choice.

I am professionally obligated to mention that Laserglow sells the Aquarius-5 which is a TEM00-TEM01 blue pointer. They're usually TEM00 at lower power levels but since temperature plays a role in determining transverse mode we can't guarantee that they will never mode hop. Blue is a finicky wavelength.

Laserglow Technologies - Handheld Lasers, Alignment Lasers and Lab / OEM Lasers

 

[anuran]

Ah, well then for the moment I will try to set things up with green and look into buying one of those blue DPSS ones. I think I'll post a new thread about the project, maybe people will find it interesting .

 

[Chicxulub]

My Aquarius is normally near-TEM00, close enough that unless you're one of us you wouldn't ever notice it wasn't. It normally only mode hops when it gets really hot or the batteries are about dead.

And that's an old batch one from 2007, the newer ones are much better.