Long-range laser range finder tear down video

[Alexei.Polkhanov]

Hi everybody,
Here is my second attempt in making a tear down video. I started videotaping some my tear downs for my own reference at first then later I decided to make videos out of them. Probably would have been better with some kind of plan

Interesting questions that I have after making this video are:
1. at around 10:32 into video I point camera into the opening inside ruby laser tube - with my eyes I see ruby/red color but on camera it shows up as green. Is this because camera's CCD is IR sensitive or perhaps some other explanation?
2. 18:45 I got mysterious discrepancy in all inductor values. I have attached a photo of an inductor - can someone tell me what its value in uH? I seriously scratched my head. Was there different color coding in 1986?

I hope I reverse engineered the triggering circuit correctly. Does it look little over-complicated for what it does?

Video:

[Alexei.Polkhanov]

Hi-res photos:
https://plus.google.com/photos/116960055711068468555/albums/6126647394166003201

[Biff383]

2.2 uH The wide silver band identifies it as an inductor.

[Alexei.Polkhanov]

So it is not 23 * 10^2 = 2300uH as I interpreted from this diagram at first. It was not clear to me how to apply dec point for military version. Make sense now.

[T3sl4co1l]

RUUUUBY RHOD https://youtu.be/OsJKdxPwZdk

[LaserSteve]

Hate to be pedantic, but you have a ND:YAG rod there. I can tell from the purple color which changes with angle and lighting.  Ruby rangefinder rods are very dark red.  I've spent much of my life working with ND:YAG and RUBY Lasers.

It will most likely lase at 1064 nanometers  unless it has a OPO wavelength converter to 1.54 microns. I don't have time to view the whole video right now as I'm at work.

The AXI modules most likely come from Analog Modules inc.

WARNING!

YOU HAVE A CLASS IV LASER!  DANGER!  DO NOT DIRECTLY VIEW THE IR  LIGHT OR ITS DIFFUSE OR SPECULAR REFLECTIONS!

The Rangefinder  Laser is Q-Switched to enhance its peak pulse power, you have a 10-20 Nanosecond pulse of immensely  intense light,

You MUST HAVE Optical Density 6 or greater safety goggles at 1064 nm to work at this wavelength, even the diffuse pulse reflected from nearby objects is a  SEVERE EYE HAZARD!   

Avoid Chinese Made EBAY Goggles for this task, you need certified OD6 or greater eye protection. Otherwise the beam path must be totally enclosed by metal. Your NOMINAL OPTICAL HAZARD ZONE  for a unit like that if  even close to having a collimated beam can be hundreds of meters or more.

So you understand what you have, find the SSY-1 at Sam's Laser FAQ. A typical pulse shaping series inductor would be about ~1000=2000 uH for a small Xenon flashlamp used in a Rangefinder.



Steve

[Alexei.Polkhanov]

The Rangefinder  Laser is Q-Switched to enhance its peak pulse power, you have a 10-20 Nanosecond pulse of immensely  intense light,
Steve

I assumed it is Q-switched because for range meter need a sharp, pulsed laser source. At first I started looking for a Pockels cell or something like that but I did not find any. I've looked around intrawebs and I found that some versions, and yes YAG laser is one of them, can be passively Q-switched. I am not sure if it has to be illuminated by flash lamp in some particular way for it to happen?

By "pulse shaping series inductor" are you referring to that black coil? I called it trigger coil. There are no other significant value inductors I found on the board.

[LaserSteve]

There should be a large inductor between the lamp and the capacitor. It may be part of the trigger coil. Otherwise this is the first rangefinder I've ever seen that does not take advantage of pulse shaping to saturate the rod and provide more precise timing. In some cases it is part of the series injection trigger coil.

The Q-switch in this case will most likely be passive, either a  Chromium Qswitch ie  either a  CR:YAG or BDN Dye based Saturable  Absorber.  It will be a intra-cavity optic that will appear brownish black if CR:YAG or be a thin polymer film with dye in it, often adhered to thin glass substrate.

Lamp Handbook, a MUST read: http://www.orcontech.com/data/Perkin_Elmer_Flashlamp_catalog.pdf

Depending on how hard the lamp is driven, the rod should be maximally pumped in  around 256 microseconds, which is the upper state storage time of common ND:YAG. A few lasers might use between one point five and two storage times to ensure saturation and maximal power.  So often pulse shaping networks are used to "bracket" the lamp pulse width around the laser pulse.

Steve

[Alexei.Polkhanov]

I think it does not need precise timing. I forgot to include it in my video but there is a small PIN photo diode mounted in a hole inside collimating lens. There is a screw that protrudes into the well inside collimating lens assembly by about 1 mm. When laser fires it (tip of the pin) is illuminated by the beam without blocking it much. PIN diode is positioned on opposite side from the pin and I believe that pulse from that PIN diode is used as t0 (time zero) for the range-finder. This way there is no necessity to have reliable timing for firing circuit - they just detect when it happens.

I looked up the photodiode they used - it appears to be a EG&G PIN photodiode just like this one: http://www.ebay.com/itm/OPTICAL-EG-G-PHOTODIODE-DETECTOR-SGD-040-LASER-OPTICS-BIN-A4-06-/261804607140?pt=LH_DefaultDomain_0&hash=item3cf4c546a4. I have better photos at home.

[Mashpriborintorg]

Thanks for the teardown, it reminds me I have a Jaguar jet fighter laser rangefinder in my garage.... I will consider making a teardown of it someday... will be a non destructive teardown, it is a collectible item.

[LaserSteve]

"I think it does not need precise timing. I forgot to include it in my video but there is a small PIN photo diode mounted in a hole inside collimating lens."

This crude beam pickoff  would support the existence of a passive Q-Switch module.  It also saved them about 400$ and some serious machining and aligning to install a optical splitter cube and an optical attenuator for the PD. . It also nicely diffuses the light to prevent the PD from burning.

Steve

[codeboy2k]

And remember Mike's warning: http://www.electricstuff.co.uk/



(click for fullsize)


Student:  "Sir, How many times can I look into a laser beam?"
Professor: "Twice."

[LaserSteve]

Let me correct that for you:


 "You can only see IR twice"...

OR "Dang!, DO NOT LOOK INTO LASER WITH REMAINING EYE"/

Seriously, Q-Switched ND:YAG generally  scares laser technicians  more then anything else. Pros treat it with the upmost respect.

Steve

[chickenHeadKnob]

What is that white creamy substance in the lasing cavity?
Interesting video by the way.

[LaserSteve]

The creamy white substance in low cost YAGs usually is a gel filled with a Barium Carbonate and a Magnesium compound that serve as a elliptical reflector to couple the pump light to the lasing rod.   Its a PITA, but its far cheaper then a polished gold reflector.   In the 800 nm pump band and the visible, that stuff achieves nearly 95% reflectivity, which is amazing. Problem is, once you remove it your usually screwed. No one has ever published how to make it.

ND:YAG is pumped by spectral bands centered on 800 and 880 nm, and somewhat by violet and green white. Nearly everything else goes to waste. Which is why more modern lasers are pumped by 808 nm laser diodes.

Steve

[chickenHeadKnob]

Thank you  Steve, your knowledge added real value here.

[Alexei.Polkhanov]

Wow I had feeling it is somehow special "chalk". I am going to try to shine some different wavelength UV LEDs on it for fun tonight. Do you happen to know what is the exact proportion? Also Wikipedia says Spectralon ($395 for "easily machinable" bar on their website - only if I got to waste other people's taxes on it! ) and powdered Barium Sulfate should be fine. Mix with water apply and let dry?

[LaserSteve]

Having seen what happens when any form of power gets on cavity optics at this power level, mere powder without a polymer binder makes for a very bad idea.

Spectralon only gets used in very high performance lasers. Its expensive unless you can buy it in bulk.

Spectralon is mainly PTFE (TEFLON)  processed in a way that has a controlled density.


Steve