505nm and 480nm diode RESULTS

Seems like I have some homework to do. I knew of temperature tuning wavelengths but not feedback tuning. Any pictures of the setup along with info on how it works?

Well...I am certainly very interested. I've got an area picked out to set my lab up once I move, and tunable lasers have always been a joy of mine. This looks like a quality way of breaking in the new space.

Is this the same single mode I will be seeing at selem? Ide love to hear about this feedback there. I also heard the laserdock update has atari games to play... defender on laser anyone?!!

Hi, everyone.
I've been doing a little research here on this 505nm diode.
To make some information regarding this diode a bit clearer, here is a plot I made from DTR's 505nm 35mW diode test video:

Pretty sure this is a different single mode.

Also that's a lot of effort. Thanks for the graph!

ZRaffleticket said:

Pretty sure this is a different single mode.

Also that's a lot of effort. Thanks for the graph!

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A different diode?
Crap.
Well, anyway, I think graphs make the data much more accessible. I'm really surprised it hasn't caught on after all these years.

RA_pierce said:

A different diode?
Crap.
Well, anyway, I think graphs make the data much more accessible. I'm really surprised it hasn't caught on after all these years.

Click to expand...

First part wasn't to you! You're good

I received my Blitz Linear drivers from Survival Lasers yesterday; very quick shipping from Gary. :yh:
These are definitely tiny, or more likely, the old eyes are getting worse, that area to bridge between those two pads for "low" range is going to be fun!
The only thing I see that I don't care for, is that there are no holes for wires, like most of Lazeerers drivers have, just small pads.

@RA_pierce, glad to hear from you again, it's been awhile! I've still got that chrome pen that I bought from you, and it's still going strong! :beer:

That was quick, Jeff. I'm hoping you will receive the diode on Monday so you can start to look at this build and the way you would like to complete it. Best wishes to you on your 503nm build.

It was very quick, surprised to to see it in the mail yesterday, along with another package from Flaminpyro that also arrived extremely fast; I don't know what's gotten into USPS lately.
I'm still needing to make a heatsink and modify a couple parts for host yet. I'll probably have a couple of questions for you when I get to building it. :yh:

No problem. I'll be happy to help anyway that I can. :yh:

BowtieGuy said:

@RA_pierce, glad to hear from you again, it's been awhile! I've still got that chrome pen that I bought from you, and it's still going strong! :beer:

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BowtieGuy said:

I... along with another package from Flaminpyro ...

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Hi!
I'm glad to hear it. Was it the ~1.5W 445 that I built for you?
Did you get a chance to put it on a power meter? Back then, all I had was a 1W Laserbee meter.

And it's good to hear Flaminpyro is still active. I'm trying to plan another chrome pen (with one of the "505" diodes - though 470 would be ideal) and I think I'll need another one of those slick stainless steel focus adapters.

CynicalBrad said:

Seems like I have some homework to do. I knew of temperature tuning wavelengths but not feedback tuning. Any pictures of the setup along with info on how it works?

Click to expand...

To understand this one have to know some basics about diode lasers. A typical diode made from GaN (~ 380nm to about 530nm) has a typical gain profile that is ~ 20nm -30nm wide. That means, that this diode can theoretically operate anywhere in this region.

One has to know, that the diode front and rear facet create a resonator, and only multiple integers of the wavelength that match the resonator length can lase, if their total gain is higher than their losses. For a typical blue laser diode (I consider only single-mode diodes for for simplicity reasons) the resonator length is about 0.05nm. Here is spectrum of a 488nm diode:




Every resonator mode that you can see in the spectrum have a total gain higher than 1. Since the gain profile of the diode is not flat only modes in the center of the profile start to lase and no more free electrons are left for the other modes in the gain spectrum.


Temperature tuning shifts the whole gain profile of a diode and therefore the center of the profile. This is the reason why temperature tuning changes the center wavelength of the laser diode.

Increasing the current increases the charge carrier density and thereby the refractive index in the diode. This also increases the wavelength of diode in addition to the extra heat generated by the current if the diode is not properly temperature stabilized.


Wavelength tuning by optical feedback works in a very different way. Here not the gain profile is shifted as a whole, but the diode is forced by lasing on only one mode (one peak from the upper figure). This is usually accomplished by using an optical element, that reflects only a narrow wavelength region. The most common one is an optical grating.

If some of the power of the first order reflection from the grating is reflected directly back into the diode, the gain for a mode at this specific wavelength is increased. With sufficient feedback from the grating this mode has now enough gain to deplete the complete diode junction alone. Then the diode operates in one longitudinal (frequency) mode.

By tuning the grating, the reflected wavelength can be changed and thus the wavelength of the laser diode. Even a mode that was not lasing at all in the free running diode (like the one around 486,5nm in the upper figure) can lase now, since their gain is greatly increased compared to the gain of modes in the free running case.

Here is a short video with a simple setup consisting of a diode and a grating
to give you an idea how this works:

https://www.youtube.com/watch?v=c4w-zhnGqCk&t=149s

Of coarse there are many various setups and realizations depending on the goal of such a tunable diode laser. I tried to scratch on the surface of this topic to give you an idea. Feel free to ask for more information. I will present my setup with some data at a later stage.

Singlemode

Very nice explanation but the image isn't showing up!

Atomicrox said:

Very nice explanation but the image isn't showing up!

Click to expand...

Should work now, and is also attached to the post.

Yes, and the diffraction grating has been etched into the diode's front facing emitter in some diodes to tune the line width to a very narrow spectral response. Of course you lose the ability to tune these externally if my understanding is correct.