405nm pointer meets Spectrometer

[ix551]

Hello there.

I recently got access to some of my campus' laser instruments for a second time.

The first time I could, I brought my 445 build to measure its power, but it LED'ed on me that same day, it was a little embarrassing

This time I went with my DX 405nm pointer link and a LOC diode.

NOTE: the batteries on the 405 were far from being full at the time of the experiments

I couldn't help but notice this little fellow:

After a lot of time setting the software and aligning the beam with my professor, we got these results:

A stands for wavelength (nm)
I'm not really sure about B.

The Spectrometer's software also threw a huge and VERY detailed list of nm values with "B" values next to them, from 405.4 all the way to 534.4.
I'll post the relevant nm range:

406.35 - 20.027
406.39 - 30.63
406.43 - 35.027
406.47 - 50.63
406.51 - 78.027
406.55 - 152.63
406.59 - 269.027
406.63 - 415.63
406.67 - 636.027
406.71 - 904.63
406.75 - 1277.027
406.79 - 1727.63
406.83 - 2199.027
406.87 - 2836.63
406.91 - 3260.027
406.95 - 3509.63
406.99 - 4033.027
407.03 - 4285.63
407.07 - 4529.027
407.11 - 5350.63
407.15 - 6544.027
407.19 - 7923.63
407.22 - 9509.026
407.26 - 10037.631
407.30 - 9208.026
407.34 - 8220.631
407.38 - 7465.027
407.42 - 6420.63
407.46 - 4805.027
407.50 - 2994.63
407.54 - 1637.027
407.58 - 826.63
407.62 - 401.027
407.66 - 181.63
407.70 - 79.027
407.74 - 24.63
407.78 - 2.027

IMO it seems that the laser wavelength is really ~407.25 instead of the 405 DX advertises.

I also attempted to measure the output power with a nice little Spectra-Physics 407A. Youtube vid here.

After several measurements the pointer only gave ~24mw, I knew it was because of the AAA batteries, which weren't anywhere near full, so I tried to power the pointer with a lab PSU, trying very carefully to set the output voltage to 3v, but the PSU gave a ~11v spike and burned the laser.

I really need to learn how to use those PSU's this is the 3rd laser I've burned this way ...the cheapest one of them

I want to buy a new 445 diode and perform the same tests soon, I need some money first tho.

 

[Cyparagon]

Die tolerance and wavelength shifting with heat accounts for your 407. If you get 4 more, you'd probably have 5 different wavelengths.

The 405 ebay pointer I have is 403nm.
The two PHRs I have are 407.5nm and 409.5nm
The 400mW O-like I have is 410nm.

 

[lazeristasUVISIR]

Die tolerance and wavelength shifting with heat accounts for your 407. If you get 4 more, you'd probably have 5 different wavelengths

The temperature change does not shift a violet laser's wavelength much (compared to red lasers) One of my was operating at 414 nm

 

[HIMNL9]

But they still shift a bit ..... and also, the manufacturers themselves usually indicates the possible wavelenghts with a discrete shift (tolerance) possible ..... like the 445, that are indicated on the datasheets as 440/455nm tolerance range .....

 

[chipdouglas]

arent phr +/- 5nm anyways?

michael.

 

[Meatball]

My BDR-205 peaked at 408nm. Diode lasers are not known for their particularly narrow bandwidth.

If it were an HeNe, a "l" is all you should expect on that graph.

 

[Cyparagon]

^Not unless the meter is worth 5-6 figures. It depends on how good the spectrometer is and how zoomed in the table is. All laser types show a similar distribution on mine.

 

[chipdouglas]

^^^check your pm's :twak:

 

[ix551]

Is the wavelength shifting also dependent on the current given to the diode? Assuming an almost perfect heatsinking system is being used so temperature remains the same

 

[lazeristasUVISIR]

Is the wavelength shifting also dependent on the current given to the diode?

Yes. I don't have a specific number at this moment.

Temperature shift for violet (405 nm) lasers is 0.04 nm/K, for NIR (808 nm) 0.25 nm/K

 

[Cyparagon]

I don't see units for current in "nm/K" sir.

 

[lazeristasUVISIR]

I don't see units for current in "nm/K" sir.

'cause I had no number. This time I have it. A wavelength shift due to current increment is 0.012 nm/mA for a ~500-mW violet laser.

 

[Cyparagon]

So you're saying if a diode was 405nm at 20mA and ambient, it would be 411nm at 0.5A while actively cooled? With all respect, that sounds like total BS.

I've got a PHR here that would be easy to test. Are these numbers of yours similar with a 100mW violet?

 

[lazeristasUVISIR]

So you're saying if a diode was 405nm at 20mA and ambient, it would be 411nm at 0.5A while actively cooled?

During the measurement it was exactly like that: started with ~407@50mA and shifted to ~410@400mA. Other interesting result was the bandwidth increased from 0.4 nm to 1 nm. The temperature was held constant of the laser mount.

Are these numbers of yours similar with a 100mW violet?

Most likely.

My numbers are not out of the blues. Friend Google extracted 0.04 nm/K for violet lasers. A book cites 0.03 nm/mA for a F-P edge emitting lasers, and a figure is in google books Zappe Laser diode microsystems.

 

[Cyparagon]

Alright, I just tested it. As I switch between 40mA and 120mA, the wavelength does change, but by less than 1nm. I'll assume it was not due to heat since I doubt the die can heat and cool within the half second it takes my spectrometer to respond to the change in current.

so (407.5nm-406.5nm)/(120mA-40mA) ≈ 0.01nm/mA, which is quite a ways from 0.04nm/mA.

During the measurement it was exactly like that: started with ~407@50mA and shifted to ~410@400mA.

Even your tests showed (410nm-407nm)/(400mA-50mA ) ≈ 0.01 nm/mA

 

[lazeristasUVISIR]

Even your tests showed (410nm-407nm)/(400mA-50mA ) ≈ 0.01 nm/mA

Even I wrote that :na: A wavelength shift due to current increment is 0.012 nm/mA for a ~500-mW violet laser.

Please don't mix nm/K (or nm/°C) and nm/mA.