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Laser modes of a green laser pointer

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Physikfan

Mon Feb 06 2017, 08:18PM

Registered Member #60240 Joined: Mon May 16 2016, 07:01PM
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Posts: 304

To all optics and spectrometer freaks

The image shows laser modes of a green laser pointer:

P1190643trim400x242

I am looking forward to your comments!

Wastrel

Tue Feb 07 2017, 12:33PM

Registered Member #4095 Joined: Thu Sept 15 2011, 03:19PM
Location: England.
Posts: 122

Potentially cool, but you've not given any context or details. Is this a Fabryâ€“PÃ©rot interferometer trace? What's the free spectral range? You look like you have problems with the trace wrapping around.

Physikfan

Tue Feb 07 2017, 04:06PM

Registered Member #60240 Joined: Mon May 16 2016, 07:01PM
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Posts: 304

Hi Wastrel

The analyzing instrument is a confocal Fabry Perot (CFP) with a FSR of 8 GHz.
The driving voltage is a sine wave of 50 Hz with about 18 Veff.
The oscilloscope is in the xy mode, x corresponds to the driving voltage of the CFP, y shows the output signal of the CFP.
Due to the hysteresis of the piezostack there is a phase difference between increasing and decreasing voltages of the same value.
As a consequence there are two traces visible a the screen.

Conundrum

Tue Feb 14 2017, 06:35AM

Registered Member #96 Joined: Thu Feb 09 2006, 05:37PM
Location: CI, Earth
Posts: 4062

Nice graph, thanks for sharing!
I seem to recall green laser pointers being DPSS, ie using nonlinear crystal to convert 808 to 1064 and doubling that to 532nm.
There was some speculation that a cheap module could be used to generate quite fast pulses by exploiting the weak piezoelectric warping of the nonlinear part but never found out how far this advanced due to the Osram direct emission diodes reaching the market.

Physikfan

Tue Feb 14 2017, 09:29AM

Registered Member #60240 Joined: Mon May 16 2016, 07:01PM
Location:
Posts: 304

Hi Conundrum and Wastrel

These green Laser pointers are infrared diode pumped Nd YAG lasers with a doubling crystal at the end.
There at least three different resonant cavities involved when switching on these laser pointers.
Switching on this laser pointer I saw at the oscilloscope screen a very fast changing pattern of modes and within a few seconds a relatively stable
picture of these modes like in the picture above.

Ad Conundrum

"There was some speculation that a cheap module could be used to generate quite fast pulses by exploiting the weak piezoelectric warping of the nonlinear part"

Please could you give me a citation concerning this remark?

"Osram direct emission diodes reaching the market."

You have mentioned the appearing of OSRAM direct emission green laser diodes at the market.
Are theses diodes relatively very expensive?
For my light speed measurements I have used only red diode lasers for creating pulses with half widths of nanoseconds.
I would like to try also green diodes.
Do you have some experience with these OSRAM green laser diodes?

...

Thu Feb 16 2017, 06:43PM

Registered Member #56 Joined: Thu Feb 09 2006, 05:02AM
Location: Southern Califorina, USA
Posts: 2445

They are readily available now, and quite cheap ($10-15 for a 10mw one)
ie

watch out, they are in a miniature 3.8mm package, so you will need a diode mount suitable for 3.8mm diodes instead of the usual 5.6mm, or buy a diode already mounted in a module with lens.

Conundrum

Fri Feb 17 2017, 04:08AM

Registered Member #96 Joined: Thu Feb 09 2006, 05:37PM
Location: CI, Earth
Posts: 4062

Indeed. I have their 450nm blue version and it was heinously Â£xpÂ£n$ive but does work well and despite an accident with one of the pins (grr!) still runs after some hair pulling and teeth grinding nanosoldering mounted to a piece of Veroboard with half an aixiz module Epoxied in place. Looks like hell but works fine for my purposes.

I would *strongly* advise paying the $$$ and getting a ready made TTL module eg from dpflaser as you will find it works much better and is more stable and repeatable in the long term than a DIY attempt.

also

Not mine alas but there are many ways to modulate power on these such as charging up the crystal (via a silver electrode) wrt ground using an HV85x or other similar small HV generator IC, what actually happens is that the crystal slightly changes shape and the 808-1064nm stage becomes less or more efficient. Doing the same to the 1064-532nm (KTP?) also works

Its worth mentioning that some laser scanners use a variant of this to scan the beam in a single axis but now MEMS is available
this is not used as much due to the simplicity of a single monolithic chip.
The Note 7 actually uses a variant of this to do its iris scanning, the chip is basically a low power version of what has been used in cameras for autofocus and face tracking.

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