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Various Spectrometer Readings

ARG

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I got a spectrometer, took some readings of various lasers, thought others may want a look. Mostly uninteresting since the DPSS and gas lasers are stable wavelengths.

405nm ebay pen


445nm 9mm diode (low temp)


473nm DPSS


532nm DPSS


Green HeNe


593.5nm DPSS


Red HeNe


635nm Mits 500 (low temp)


Dollars store laser


650nm LPC-826 (low temp)
 
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ARG

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x axis is wavelength (in nanometers)
y axis is intensity

Lasers are coherent, so you need to look at where the peak is. Where the peak is at is the wavelength of the laser.
 
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Meatball

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The HeNe and DPSS readings are a little concerning. They really should be much more narrow banded than they appear to be. The HeNes and DPSS lasers especially should not have any of that junk that slopes off towards the higher wavelengths - the 532 in particular since it has no other "emission lines" that should be anywhere near the 532.

I can understand diodes are kind of silly looking, but a bandwidth of 30-40 nm is quite ridiculously more like an LED. The 660 should not be so bad, the 405 looks more realistic if it were a broad diode to begin with, but that 9mm diode spectrum is a little hard to believe.

Do you understand my concerns here? I wonder what kind of "noise" is being splashed all over the specs' CCD array. These readings look very wide!
 

IsaacT

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Very interesting! How much did the Spectrometer run you if you don't mind my asking? Also, what current were you running the 445nm 9mm diode at? I do see it is low temp, but curious nonetheless....does a higher current push the wavelength up or down?

Thanks,
Isaac
 

ARG

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Very interesting! How much did the Spectrometer run you if you don't mind my asking? Also, what current were you running the 445nm 9mm diode at? I do see it is low temp, but curious nonetheless....does a higher current push the wavelength up or down?

Thanks,
Isaac
Wavelength increases as temperature increases IIRC, I've yet to test this for myself.
The current on the 9mm diode was 15mA, just testing it out :p

The spectrometer was 400$ (calibrated) you can buy them for 200$ (uncalibrated) on ebay.
This guy sells them calibrated (you have to wait for a good price, one went for 365$ right after I got mine for 400$, but most go for 550$+ most have gone for 700$)
Laser Lab Fiber Optic Coupled Portable Optical Spectrometer USB Serial Ocean | eBay

Uncalibrated:
Compact Fiber Coupled CCD Spectrometer Kit (DIY) | eBay

Edit: @Meatball
It has to do with how I was taking the readings, take a look at the 532nm reading I got after playing with how the light was going into the fibre, the gap is ~5nm smaller.


Edit2: Yup, got a MUCH better HeNe reading when it's pointed at the sweet spot.


Edit3: Found an even better spot, getting 2nm gaps now, looks like other peoples readings now :) Correct me if I am wrong though, isn't the tip of the parabola the important part when reading coherent light?
 
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Meatball

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Well hey, those look much much better!

Peak wavelength is indeed the most important figure to consider. Alignment, noise, and calibration all affect the measured lines and bandwidth. Yours is a fiber fed spec, which is probably the best in my experience.

Consider the 532nm. The DPSS process creates exactly that wavelength (521.9xxxxxx) down to several decimal places.

Now, some of that number can be changed depending on the doping of the YAG or the YV04 but it all comes out to 532.xxxx something in the end. The point of this is, that it is indeed exactly one wavelength emitted by the KTP/LBO set. By the time the light gets bounced around in the fiber, and is read inside a device at 1 ATM pressure, the wavelength might be measured with some "noise" or bandwidth not previously predicted. So peak is definitely important for DPSS and gassy setups.

Feeding a fiber can be tricky. Sometimes I have to feed 150um fiber apertures. I don't know the size of your fiber, but if you actually focus the beam into the fiber with an ordinary lens, you can be given more freedom with which to "explore" the fiber aperture looking for the sweet spot. You shouldn't need micron adjustments to make this work on yours.

Don't EVER focus anything > 40mws onto the fiber aperture however. For high power lasers, focus the dot onto a surface which will not be burned, or fluoresce (like a graphite sheet). Then from the dot, use an ordinary lens to focus the scattered reflection of the dot into the fiber.

You should be able to achieve a VERY nice and tight focus into the fiber, and a very clean signal without noise (if you turn off the damn lights) and you won't burn the fiber tip while you get things aligned.

If you're measuring a multi-line laser, or even fluorescence, the same process can be used. Just do everything you can to keep the noise down, and alignment becomes a cinch!

Now get a green diode on that thing! :beer:

Tyler
 

ARG

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Thanks for the tips Tyler! I'll be sure to check out a green diode when I get one :)

The way I was doing it for the bad readings was reflecting the lasers off my stainless steel torch and measuring the scatter. The better ones were taken with pointing the laser at the white ceramic of a TEC and measuring from the scatter off of that, but the sweet spot is when the fibre head was parallel with the beam of the laser. (I don't know why, I will have to experiment with this)

The fibre I have is 150um (at least that's what the auction says), I'm glad to know I can put some power into it, I was afraid to directly shine my 2mW laser in.

Do you by chance have a reading of a Mit's 635nm diode I could compare to?
 

Meatball

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I don't have one on hand, but I can get one for you. How soon do you need it?

For those goofy measurements, did you just "point" the fiber at the dot, or did you put a lens in front of the fiber to focus it? The lens adds back some directionality (hence ability to align) to the scattered light - but at a reduced intensity.

But you know what, I don't know if your CCD is temperature controlled or not. I can actually get away with 50mws into the spec I use, but I think I can do so because it is also actively cooled, I set it to -10 degrees C. Assuming yours is not cooled, probably best to keep it under 20mws.

I used to have an ocean optics manual available to me, but I'm not sure where to get one now. I could check online, but I'm sure you already have!

EDIT: For the 635nm diode reading, I could do the measurement along with a required temperature at the diode, and I have a variety of gratings to choose from. I could go with a 2400 lines/mm resolution which gives (hundreths?) a fraction of a nm. The measurable band is reduced to ~15nm as a consequence though - shouldn't be an issue.
 
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ARG

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Any time that's good for you, my spectrometer is still being a bit strange past the HeNe line (perhaps needs recalibration beyond that point)

For the goofy measurements I just pointed the laser on the torch so that the reflection blanketed the fibre head. I have some lens' that I can test to focus the beam.

My spectrometer CCD is not temperature controlled as far as I know (I didn't even know spec's could come with that!)
What spectrometer do you own?
 
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I wonder where the Osram PLTB450 falls on this graph? i just got 2 single mode 450nm from the laserBTB GB and wonder if there really 450nm. I know there single mode but thats all i'm sure of.
 

Meatball

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Any time that's good for you, my spectrometer is still being a bit strange past the HeNe line (perhaps needs recalibration beyond that point)

For the goofy measurements I just pointed the laser on the torch so that the reflection blanketed the fibre head. I have some lens' that I can test to focus the beam.

My spectrometer CCD is not temperature controlled as far as I know (I didn't even know spec's could come with that!)
What spectrometer do you own?
I'll see what I can collect for you. I've got a 300mW mits I can test out.

If you have any harvested casio projector optics lying around, they should work very well. Find a collecting lens at least 3 cm diameter, and then a coupling lens (probably < 3 cm) to focus the spot into the fiber. The larger that first lens is, the easier it will be to focus into the fiber after the second optic. You could machine a small mount to keep them in line with each other, and stick it on a small camera tripod mount for easy alignment after the laser is turn on - lots you could do to make life a bit easier on yourself.

I use an Andor Shamrock 303i at work. Its gated for time resolved emissions, and self calibrates and everything. I wish it was my own!

What do you mean beyond the HeNe line? The stuff > 543? The calibration itself might not be so bad on the accuracy dimension, but the incident beam could be out of focus as it lands on the CCD. Could be re-focused if you're patient. I think there's a cylindrical lens you would have to rotate.. carefully. I think I've alignment instructions for that spectrometer typology - let me know if you want them, I can dig them up again.
 

Pman

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Repeat after me.
I don't need one, I don't need one, I don't need one...:crackup:
 

Blord

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I wonder what my 520nm laser would give but no way that I sent a complete laser to Canada.
 




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