Science surplus spectrometer calibration help needed.

So, I bought a science surplus spectrometer a few weeks ago and finally got to calibrating it. It has a 1800 l/mm grating installed. For calibration I used a used a mercury vapor black light lamp, 175W mercury vapor lamp, 532nm green laser and a red HeNe.

After recording the pixel number of light sources listed above I fit the numbers to a 3rd degree polynomial. This equation generates the coefficients the software needs to convert the ccd pixel number to wavelength.

Everything looks good so far. I tested the spectrometer with the 532 laser and the HeNe. Dead on. Next I checked with the blacklight bulb. The Uv spectrum is just slightly off a few nanometers. Close enough to get started I thought. First I checked the WL of a cheap red pointer... 660nm. Good! I'm thinking I must be close. Next, I checked one of the new 465 diodes. This came in at around 446nm. Certainly not right. The lower end must be off enough to cause this I though. Moved on to a g71 diode. This thing measured around 624nm. Thats not right! hooked up a oclaro 700mw red. Same thing 624nm. This should be higher than the HeNe. Hmmm..

Ok, so next I reset the software to read pixel number again. I measured the HeNe as a known baseline then shone the Oclaro diode on the fiber input at the same time. It is showing a lower pixel number than the HeNe. How is this? The cheap red pointer also shows a lower pixel number.

At this point I am confused. I haven't opened the unit up yet. Maybe another diffracted order is bouncing off something. But then the CCD would show two lines at once.

Help....

They need to be aligned... Check out Wolfgang's site for information: http://hololaser.kwaoo.me/electronics/spectrometer.html

Here is where to download the information to align the BWTEK spectrometers. These were sold on ebay from science-surplus.

http://www.science-surplus.com/produ...edirects=0&d=1

I have one too, but have yet to align it.

-G

Thanks for the links.

I think I will try to calibrate the longest wavelength to a 660nm diode as this would be the lowest freq I should need.

Currently the laser lines look very symmetrical and the curve fit to the wavelengths I used is only slightly curved. Im still scratching my head as to why the laser diode reads lower nm than the HeNe?