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Metrologic ML855 HeNe Laser

rote:

hing like that (when no students are around, of course). Maybe I'll get luc ky and the tube will still work. Otherwise, I'll talk to some friends in la bs about a Helium soak.

h a red diode laser? ~$10 or so.

h our interferometery apparatus.

e coherence length 'swish' around as the different longitudinal modes cross over the gain curve. But that seems like a bit of an esoteric difference f or the 'normal' high school laser application.

nal

;-)

Hi Sam, Thanks for the response. You're talking about sending the laser in to a F-P and looking at the output? A flat mirror F-P (Etalon), a confocal curved mirror F-P, or something in between?

Yeah there are lots of fun things if you allow for access to the cavity. I recall fondly an argon laser in grad school, that was equipped with a grat ing and mirror on one side... you could tune through all the Argon lines. There is a certain beauty in the 'pure' blue colors.

Thanks Again,

George H.

is

in the

Reply to
ggherold
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The kid did have holes in his iris, maybe he experimented with other more powerful lasers that I didn't know about. Chuck

Reply to
chuck

OK that's good to know. It'd be nice if someone had a list of good diode lasers. The one we use is from US lasers M650-5I. ~$33 from digikey. We have a couple of others but I never looked at the coherence length.

George H.

Reply to
ggherold

Generally, a confocal FP is best since it greatly simplifies alignment.

For the HeNe, the mirror Radius of Curvature (RoC) of both mirrors needs to be less than about 50 mm so that the Free Spectral Range (FSR, or mode spacing of the FP) is larger than the gain bandwidth of the HeNe red transition.

One of the FP mirrors is then mounted on a piezo transducer (PZT) and the FP is scanned rather than the laser. The PZT can be the beeper element from a digital gizmo or less than $2 from Digikey. :)

More info at:

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Reply to
Samuel M. Goldwasser

with a red diode laser? ~$10 or so.

with our interferometery apparatus.

h the coherence length 'swish' around as the different longitudinal modes c ross over the gain curve. But that seems like a bit of an esoteric differen ce for the 'normal' high school laser application.

gh

ool.

art. ;-)

OK you may like this, I have only a few youtube videos.

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I'm sending a diode laser into a confocal cavity, (20 cm mirrors) with the cavity length set maybe 1cm short, so all the modes, don't all fal l at the same wavlength. I'm then scanning the laser wavlength, and have a bare CCD camera (no lens) pointing into the back end of the cavity. This video has mostly just the even modes* but the others show both odd and even .

George H.

*if you get the laser 'smack dab' down the middle you lose 'most' of the od d modes.

is

in the

Reply to
ggherold

I assume you are seeing a combination of the laser modes (if not single longitudinal mode) and the off-axis cavity modes. It may be possible to determine the spectrum of the diode laser from the video but that's above my pay grade. :)

--
    sam | Sci.Electronics.Repair FAQ: http://www.repairfaq.org/  
 Repair | Main Table of Contents: http://www.repairfaq.org/REPAIR/  
+Lasers | Sam's Laser FAQ: http://www.repairfaq.org/sam/lasersam.htm  
        | Mirror Sites: http://www.repairfaq.org/REPAIR/F_mirror.html 

Important: Anything sent to the email address in the message header above is 
ignored unless my full name AND either lasers or electronics is included in the 
subject line.  Or, you can contact me via the Feedback Form in the FAQs.
Reply to
Samuel M. Goldwasser

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