Confirmed cheap multi-line 980nm/490nm pen

[Mattronium]

Re: Possible cheap 2-line 980nm/490nm pen

I'm just wondering, would it be possible to use a KTP from a 532nm laser to double the 980nm to 490nm "more" efficiently? I know there are the coatings that probably won't work at the 980nm/490nm, but could it work at all to get at least a little more than the trace line in the 980nm pens.

Probably not possible, but I just had to ask the question

 

[Sigurthr]

Re: Possible cheap 2-line 980nm/490nm pen

It's all about the mirror coatings, Mattronium.

 

[zyxwv99]

Re: Possible cheap 2-line 980nm/490nm pen

On a completely unrelated tangent, I found some more info on human vision in the near infrared. Until today, the best info I had was Sliney (1976) where a 1064nm laser with 3mm diam. beam shined into 20-minute dark-adapted eyes needed an average minimum power of 0.069 mW for threshold visibility (with full color saturation at threshold, as is the case with longer wavelengths). At 1150 they estimated it would take 3-4mW, but were unwilling to go above 2.5mW for safety concerns.

Since the sensitivity of the eye declines by about an order of magnitude every 50 nm in the near ir, I figured somebody should be able to see 1200nm if they were willing to take a chance.

It turns out that in 1980 some Soviet researchers decided to give it a try. They got people to see 1130.3 with 5-10mW of power, and 1271.4 with 30-50mW.

HumanPerceptionOfInfraredLasers
click on the link that says (Download 198 KB pdf) and you'll get an English version of the original research paper.

http://poseidon.sunyopt.edu/zaidi/p...ght second harmonic generation in the eye.pdf
see the bottom of the table on the second page

By the way, if anyone is looking at the faint cyan dot from this thing with dark-adapted eyes, the dot too faint to really see the color, here's a point to ponder: how safe is it to look at an 80mW dot at close range with wide-open pupils? Just because you can't see the 980nm doesn't mean it isn't there. Let's make sure we all have our 980nm safety goggles.

 

[Atomicrox]

Re: Possible cheap 2-line 980nm/490nm pen

Interesting papers as always, zyxwv99. Russians always do the crazy stuff

 

[ultimatekaiser]

Re: Possible cheap 2-line 980nm/490nm pen

Interesting, its definitely not impossible either. I did some digging this morning, and most 980nm diodes use a InGaP or InGaAs emitter. Though the InGaP is a bit more common due to its higher output and In(II) has several emissions possible in this range. I believe the P is responsible for the main emission at 979.7nm, but In (II) has two probable emissions at a very low order of magnetude at both 490.5 and 491.5 that could be the culprits, and P (II) has a line hardly mentioned anywhere at 493.6, but that one seems less likely.

 

[bloompyle]

Re: Possible cheap 2-line 980nm/490nm pen

Interesting, its definitely not impossible either. I did some digging this morning, and most 980nm diodes use a InGaP or InGaAs emitter. Though the InGaP is a bit more common due to its higher output and In(II) has several emissions possible in this range. I believe the P is responsible for the main emission at 979.7nm, but In (II) has two probable emissions at a very low order of magnetude at both 490.5 and 491.5 that could be the culprits, and P (II) has a line hardly mentioned anywhere at 493.6, but that one seems less likely.

Very interesting. Thank you for sharing!

I wonder if these lines are seeing attention in the direct diode industry. I'm sure they are given how readily available information is on them. If it's a lasing line, I wouldn't be surprised if emitters have been mirrored/coated specifically for such.

 

[The_LED_Museum]

Re: Possible cheap 2-line 980nm/490nm pen

Just wanted to let everybody know that I received this laser today -- and yes, the 490nm line is visible. I can't perform any spectroscopy though until I find my 473nm blue DPSS laser that has an easily-removeable NIR filter.

 

[The_LED_Museum]

Re: Possible cheap 2-line 980nm/490nm pen

A ? for everybody:
Does anybody have a NIR filter that I can borrow so that I may attempt spectroscopy on the very weak~490 nm laser line?

I found my 473 nm DPSS laser, but the section containing its NIR filter was nowhere to be found.
I have just 90¢ in the bank right now; otherwise I'd just purchase my own.

My address is:

The LED (and Laser) Museum
C/O Craig Johnson
1027 Ellinor Ave.
Shelton WA. 98584-1115

Thank you ever so much ahead of time!!! :wave:

 

[The_LED_Museum]

Re: Possible cheap 2-line 980nm/490nm pen

I just obtained photographic evidence of the ~490nm laser emission.

To wit:

I used the NIR filter assembly from my yellow DPSS laser; however, since this filter ass'y also contains the collimating lens, I'm not able to use it for performing spectroscopy.

 

[Atomicrox]

Re: Possible cheap 2-line 980nm/490nm pen

Cool, is that the aperture or a dot on the wall?

I'd send you a filter if I lived in the US.

 

[The_LED_Museum]

Re: Possible cheap 2-line 980nm/490nm pen

Cool, is that the aperture or a dot on the wall?

I'd send you a filter if I lived in the US.

That's the aperture -- 'looking down the barrel' as it were.

 

[The_LED_Museum]

Re: Possible cheap 2-line 980nm/490nm pen

I checked both last night and this morning; the weak secondary emission is visible as a cyan (blue-green) dot (not grey) on a white surface in a darkened area; it also has significantly higher divergence than the primary 980nm beam does. The beam terminus spot increases in size quite rapidly as the laser is moved away from the surface; the cyan dot appears to double in diameter from the laser aperture being point blank to being pulled approx. 1 foot (0.3048 meters) distance.

Just a simple curious observation, not empirical scientific data. op:

 

[Blarg King]

Re: Possible cheap 2-line 980nm/490nm pen

Played with mine and noticed a similar effect. From about 2 inches away the cyan dot becomes the size of a quarter. Interesting how its divergence is different than the IR even though its emitted from the same spot and goes through the same optics.

 

[bloompyle]

Re: Possible cheap 2-line 980nm/490nm pen

I have yet to buy one of these ...

When I have more fun money, I will grab a decent output diode and run some tests.

I'd REALLY like to get is a good quality mirror as an output coupler for the ~490nm. Something like 95-98%R @488-493nm.

Theory being that it won't be enough return power to kill the mirror, even intracavity. Though it could get us some more gain if we're lucky. I need to look into basic functionality of semiconductor lasers to see if such a thing is even possible.

If not. Perhaps two OC's external to the laser. M1 with borderline HR properties, and M2 as an output coupler with something like 95%R. Make something like a HeNe.

Though then you might as well have just invested in 980nm mirrors and an LBO....

Worth looking into for sure.

 

[Atomicrox]

Re: Possible cheap 2-line 980nm/490nm pen

Perhaps the second line power/brightness has more variation than the IR line. Mine is way too weak to notice divergence at 1ft.

 

[Atomicrox]

Re: Possible cheap 2-line 980nm/490nm pen

Update!

I performed this experiment again, this time using two stacked IR filters and more wavelengths:
-980: cyan emission caught on camera and by eye
-850: no emission caught on camera or by eye - with a single filter the camera caught a weak IR emission, didn't try by eye
-808: strong ir emission on camera, didn't try by eye because even with two filters it's still a couple of mW on my LPM - I need a weaker 808nm laser!
-780: weak red (IR) emission caught on camera and by eye

So as far as I can tell this phenomenon is unique to the 980nm.

Also note that of all those IR lasers the only one that I can't see the IR dot on a wall is the 980nm. All others are still "visible".