B&W-tech Spectrometer & 473 module: Setup+Mods+Info

[jnrpop]

Re: B&Wtech 473nm unit / Spectrometer Mods & Info

Success!!
After removing the filter, the spectrum opens up.
I'm reading pixel 299-2047 now using an LED source. My 475nm build didn;t register on the sensor before, now it does. It registers in at 485nm, so i believe i still need to calibrate, but looking better than before

:beer:

 

[diber]

Re: B&Wtech 473nm unit / Spectrometer Mods & Info

Good ! Glad my comments could help!

In order to decide if it is necessary to remove the filter for a specific application or not, I measured the filter transmissivity with another spectrometer I have (monochromator with PMT) using a normal mains-powered halogen lamp as illumination source. The plots are attached (sorry for the low quality due to resizing of the screenshot). Blue is illumination source without filter, yellow with filter and red transmissivity (x10). Ignore the noisy results below 400nm and above 850 nm due to the fact that the lamp does not illuminate in these spectral ranges). Conclusion: almost no transmission below 475 nm (I measured 2% at 473nm for this filter, less on another filter, explaining why you can still see the intense laser line of the 477nm laser or in some cases even the 473nm laser). Transmissivity ramps up to >95% between 475-523nm and remains constant (approx 97%) up to at least 820nm.

I did not re-install the black cylinder in my spectrometers. Actually, I prefer to keep the filter inside it to protect it a bit during storage. It could be that there is maybe an effect on internal straylight when removed ? But as said, so far I keep it out.

 

[paul1598419]

Re: B&Wtech 473nm unit / Spectrometer Mods & Info

Thanks for that information, diber. I can see the 477nm laser overcoming the filter's attenuation, so that makes perfect sense. I am still too busy to get back into mine yet.

 

[Atomicrox]

Re: B&Wtech 473nm unit / Spectrometer Mods & Info

Did I misunderstand or are they able to read the whole visible spectrum without the filter?

 

[paul1598419]

Re: B&Wtech 473nm unit / Spectrometer Mods & Info

They can read ~200nm of spectrum without the filter between ~473nm to 650nm. Give or take a bit.

 

[jnrpop]

Re: B&Wtech 473nm unit / Spectrometer Mods & Info

I found some time to do some more work on my Spectrometer software.

For now we can just use Excel to calculate the 3rd Order Polynomial values. It was pretty easy to use excel to calculate the variables I, C1, C2, C3. Link to the Ocean Optics PDF file explaining how to do it - Instructions.pdf

I have added the calibration to my code. I have calibrated my Spectro using 4 pointers. 473, 505, 532 650.

Wow, After plugging the data into Excel. Calculating the calibration data. Putting the data back into the Spectrometer software. It's bloody accurate. All 4 pointers read exactly what they should read.

I have added two text boxes under the graphed data. One shows Pixel Number and the second shows Wavelength. Just move the mouse to the point on the graph you wish to find the data and its shown under the graph.

One interesting thing I have found after calibrating is the bandwidth on my Spectrometer is actually 457 to 651. It looks like the Grating does need changing. The bandwidth is very small.

I would say Mosc was spot on in this post from way back.....457-651, with the baffle and filter removed :beer:

I'm still reading up how to calibrate my unit. I have a handful of wl's to use, just need to figure out how to do the calc.... :thinking:

 

[paul1598419]

Re: B&Wtech 473nm unit / Spectrometer Mods & Info

I can help you with that later if you have trouble figuring it out, Corey. You need to solve for y= I+C1*X+C2*X^2+ C3*X^3. The constants you want are I, C1, C2 and C3. I'll have more time later on to help more if you need it. :yh:

 

[jnrpop]

Re: B&Wtech 473nm unit / Spectrometer Mods & Info

I can help you with that later if you have trouble figuring it out, Corey. You need to solve for y= I+C1*X+C2*X^2+ C3*X^3. The constants you want are I, C1, C2 and C3. I'll have more time later on to help more if you need it. :yh:

Appreciate the offer Paul :beer:

So, from what i've read and think i understand, I is the λ @ pixel 0.
Pixel 1 on Moscs software is 458.2nm, can't see pixel 0.
C1,C2,C3 are recorded with three different λ's (eg: 532nm dpss,450nm diode ,632.8nm HeNe, etc )

And then using excel, i plot a spreadsheet using the format posted a few posts back.

J

 

[paul1598419]

Re: B&Wtech 473nm unit / Spectrometer Mods & Info

You should use as many stable laser sources you can get. Not direct diode lasers as they drift. Also get some lines as close to 460nm and 650nm as possible because the curve doesn't extrapolate well at all. The more lines you get, the more accurate the spectrometer will be. I have 473nm, 488nm, 532nm, 632.8nm and a coupe others I don't remember off hand.

 

[diber]

Re: B&Wtech 473nm unit / Spectrometer Mods & Info

A CFL lamp is also a good calibration source with well defined peaks over the full range of the spectrometer. Annotated spectra, with indication of the WL of the peaks can be found on the internet.

Related to the calibration coefficients: excel can do the best fit. Another way is to use the "Spectrum Studio" software. When clicking the tools button, you can find a tab "Least Squares Fitting" in which you can enter the table of pixel number/WL pairs. Coefficients are calculated and displayed while you enter the calibration peaks.

 

[paul1598419]

Re: B&Wtech 473nm unit / Spectrometer Mods & Info

Unfortunately, most members here don't have discharge lamps, so lasers are the next best thing to use. IIRC, Ocean Optics uses ArXe lamps. I need to find a good source for some at reasonable prices along with the spectra for each.

 

[Cyparagon]

Re: B&Wtech 473nm unit / Spectrometer Mods & Info

most members here don't have discharge lamps

I've mentioned these several times before, and I feel like I'm being ignored.
Maybe pictures will help.

See this little doohickey here? This is called a CFL. It is a discharge lamp with 5-6 easily identifiable atomic emission lines. My dollar store sells 4-packs of these.

See this little doohickey here? This is called a neon indicator lamp, which is a type of discharge lamp. It has over a dozen easily identifiable atomic emission lines from yellow to NIR. They are commonly found illuminating switches in power strips and many other devices. They're a dollar or three at your hardware store.

So don't tell me "most members here don't have discharge lamps".

 

[Nexgen]

Re: B&Wtech 473nm unit / Spectrometer Mods & Info

Just bought two of these units off eBay, really caught my eye. I will post images of 473 inside, wondering if I get one with beam correction optics inside, it was said that those are good for DIY 532nm, luckily I got some spare crystals to do so

 

[diachi]

Re: B&Wtech 473nm unit / Spectrometer Mods & Info

Just bought two of these units off eBay, really caught my eye. I will post images of 473 inside, wondering if I get one with beam correction optics inside, it was said that those are good for DIY 532nm, luckily I got some spare crystals to do so

I meant to check mine to see what optics it had in it... The last one I had didn't have any correction optics other than the pump focusing lens, haven't checked this one yet.

 

[LSRFAQ]

Re: B&Wtech 473nm unit / Spectrometer Mods & Info

For those who are wondering about the exact wavelength of the B&W Tek Blue DPSS, I had to do some serious digging in a academic data base.

I had seen 472.73 mentioned before as the wavelength for a DPSS Blue..
But I wanted to do some digging before trusting the blue line for calibrating a spectrometer...

Turns out the ^4F3/2-->^4I9/2 transition is a quasi three level system and can lase from 945.46 to 946.29 and the center of the gain profile is approximately 945.905 nm. When frequency doubled that means the blue
can be from 472.73 nm to 473.15 with a center of 472.95, and a gain bandwidth of about 0.42 nanometers.

Hence why Blue Nd:YAG dpss is designed for careful temperature controls, its easy to hop off of the center of the gain curve. If you want a stable 473 you need to consider running single frequency using a etalon or other means.

REFERENCE:

Frequency stabilized diode-pumped ND:YAG laser at 946 nm with Harmonics at 473 and 237 nm G. Hollemann Et Al.. Optics Letters/ Vol. 19 No. 3 / February 1, 1994 Optical Society of America, Publisher.


Steve

 

[paul1598419]

Re: B&Wtech 473nm unit / Spectrometer Mods & Info

Thanks for that information, Steve. I was wondering exactly where on the spectrum these 473nm DPSS laser might be. I will eventually get back into the lasers on these and this information helps me a lot.