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Review of a Metrologic ML-868 Neon Laser

The_LED_Museum

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This is a long page with at least 29 images on it; dial-up users please allow for plenty of load time.

Metrologic ML-868 Neon Laser, retail $575.00 (www.i-fiberoptics.com...)
Manufactured by Metrologic (www.i-fiberoptics.com...)
Last updated 12-09-11









This is the Metrologic ML-868 helium neon laser (they call it a "neon laser"). This model (and other models of Metrologic HeNe lasers) was most frequently used in high school physics laboratories in the 1980s.

When I was 12 or 13, I had a Metrologic ML-800 Neon Laser (back when I lived in Juneau AK. USA); so this is definitely a blast from the past.

On the off-chance you ever come across a Metrologic ML-800 with the number "789-7610" engraved on its bottom, that's mine (it was stolen in the mid-1980s), and I'd really like it back.

The ML-868 features a "hard sealed" plasma tube; which they claim extends the tube life to 20,000 hours.
They do not specify whether this is operational life or shelf life however.
Plasma tubes, unlike diodes, ever so slowly degrade whether you use them or not.

This is one case, however, when vacuum tubes are better than solid state: the beam emerges in a true Gaussian profile (brighter center falling off to extinction) and the coherence length could be measured in meters, instead of in millimeters for most diode lasers, which makes producing and viewing holographic images much, much easier.

The model ML-868 is modulated, meaning you can input audio and/or video signals into the laser and transmit them to a receiving unit positioned a reasonable distance (line-of-sight) away.

Regarding the third photograph above, note that the inside surface of the laser aperture is threaded.


SIZE



Electrically, this laser is easy to use; just follow these three steps:

1: Plug it in to any grounded (three-slot) standard (in north America anyway) 110 to 130 volts AC 60Hz receptacle.
2: Slide the power switch on the back of the unit to the "ON" position.
3: With the laser rightside-up & facing you, slide the beam shutter on its front toward the right until it no longer moves.

When you're finished using it, slide the switch to the "OFF" position, slide the beam shutter to the left, and unplug it.

This laser has inputs for audio and video modulation, but as there was no documentation furnished with the laser, I do not know how to use the modulation or the voltages necessary for these inputs.

(Update 02-26-07): The audio connection is 100mV peak-to-peak level and 8K ohm impedance, and the video connection has a maximum bandwidth of 1MHz - a black & white video camera should interface successfully. I believe standard low level video signal voltage is appropriate.

(Update 03-01-07): The voltage level for composite video is 1 volt peak-to-peak.
That consists of 0.7v of video information and 0.3v of sync.






Photographs of the back (left/top) and front (right/bottom) of this laser.

According to a label on its bottom, this laser was manufactured in January 1988.

The beam diameter at exit is 0.75mm and the divergence is 1.1mrad (milliradians).

I do *NOT* know how the beam is modulated; gas discharge tubes tend to want to stay at full brighness if you attempt to modulate them by modifying their power input parameters at more than a few tens of Hz.; yet this laser is modulatable at speeds up to 1MHz.


This is labelled as a BRH Class II laser.
BRH stands for "Bureau of Radiological Health", and was what we called the CDRH (Centers for Devices and Radiological Health) back in the 1980s. The laser power level classifications are identical; only the name of the bureau was changed.

The only other significant difference in labelling appears on the front of this laser.
This laser was manufactured in 1988, and it reads:

AVOID EXPOSURE
LASER LIGHT IS EMITTED
FROM THIS APERTURE


Whereas my ML-800, manufactured in the early-1980s, read:

AVOID EXPOSURE
LASER RADIATION IS EMITTED
FROM THIS APERTURE


The warnings mean exactly the same thing; only the word "radiation" was replaced with the word "light".




Beam photograph on the test target at 12".
Beam is not yellow in the center as depicted in this photograph.
Measures 0.756mW on a laser power meter.
After ~12 hours continuous operation, output measures 0.792mW.
This laser was originally designed to output 0.8mW, so this is well within limitations.



Beam photograph on a wall at ~10 feet.



Spectrographic analysis of this laser.



Same as above, but spectrometer's response band narrowed to a range of 625nm to 645nm.



Spectrographic analysis of this laser; newer spectrometer software settings used.
Spectrometer's response narrowed to a band between 628nm and 638nm to pinpoint wavelength, which is exactly 632.00nm.
Spectrum was taken approx. 30 seconds after power-on.




Spectrographic analysis of this laser; newer spectrometer software settings used.
Spectrometer's response narrowed to a band between 628nm and 638nm to pinpoint wavelength, which is 632.248nm.
Spectrum was taken approx. 15 minutes after power-on.




Spectrographic analysis of this laser; newer spectrometer software settings used.
Spectrometer's response narrowed to a band between 628nm and 638nm to pinpoint wavelength, which is 631.9nm.
Spectrum was taken approx. ten hours after power-on.




Spectrographic analysis of this laser; newer spectrometer software settings used.
Spectrometer's response narrowed yet more to a band between 631nm and 633nm to pinpoint wavelength, which is 631.998nm.
Spectrum was taken approx. ten hours after power-on.



Spectrometer's response band narrowed to a range of 375nm to 600nm to show non-laser emission lines.
This is through the tube's OC (output coupler).



Same as above; but with trendline (baseline) electronically masked.
This is through the tube's OC (output coupler).



Same as above, but with spectrometer's color fill disabled.
This is through the tube's OC (output coupler).



Specrographic analysis of this laser tube's discharge column.



Same as above; spectrometer intentionally "overloaded" to show weaker spectral lines.

USB2000 spectrometer graciously donated by P.L.




Beam cross-sectional analysis.
Image made using the ProMetric System by Radiant Imaging.




TEST NOTES:
Test unit was purchased on Ebay for just under $90.00 on 02-15-07, and was received on the afternoon of 02-26-07.

It came with the Metrologic #45-600 Laser Optics Lab; consisting of numerous mirrors, prisms, slides, holograms, mounts, optical bench, etc.
As time permits, I *may* experiment with it, but no guarantees here.




UPDATE: 06-07-07
O NOOOOOO!!!!!
The high voltage side of a helium-neon power supply arced to the outer casing of this laser yesterday, blowing the fuse. When I got more fuses this morning, I installed one...poof!!! So I put in another. Poof! The "power on" indicator glows for 50ms to 100mS (1/20th to 1/10th of a second), then goes out as the fuse blows. No lasing is noted. Since I'm not sufficiently knowledgeable in high voltage power supplies, I think this poor little laser is a total loss.




UPDATE: 06-09-07
I have heard from somebody at Metrologic's educational lasers and fiber optics division that this laser may *NOT* be a total loss after all - that it may be able to be repaired for far less than the cost of a replacement. He asked me if I wanted an RMA number, of course, I said "yes please". Once they receive the laser, they'll give me an estimate on its repair cost...if I can afford it, I'll have the laser repaired.
I'm expecting some money in mid-July 2007, so I'll probably be able to afford it.





UPDATE: 11-07-07
This laser is now back, and it appears to function properly.
That's all, folks!





UPDATE: 11-18-08
I have been furnished with correct URLs (links) to this laser by the company that purchased Metrologic Instruments' educational division in November 2004; the links near the top & bottom of this web page were replaced.







MANUFACTURER: Metrologic
PRODUCT TYPE: Plug-ready HeNe laser
LAMP TYPE: HeNe plasma laser tube
No. OF LAMPS: 1
BEAM TYPE: Very narrow spot
SWITCH TYPE: Slide on/off
CASE MATERIAL: Metal
BEZEL: Metal; threaded male collar for accessories
BATTERY: N/A
CURRENT CONSUMPTION: Unknown/unable to measure
WATER-RESISTANT: No
SUBMERSIBLE: NO WAY HOZAY!!!

ACCESSORIES: None
SIZE: 32.80cm L x 7.20cm H x x 7.40cm W
COUNRY OF ORIGIN: USA
WARRANTY: 2 years




PRODUCT RATING:


This is a vintage laser (this particular unit is!!!), so conventional ratings will not be assigned to it.
You can still purchase this laser from the manufacturer at the link near the top of this post, so this review is kosher to post pretty much any place that seems appropriate.

 
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