I have an industrial application where operators use a red visible light pencil beam laser for guidance; visible laser diode, 2.2 mW, 635 Nm. The laser is mounted on a tripod and is battery powered with no control signals and is aligned using surveyed control points. The distance between the laser and target ranges from 40 to 150 feet in a dusty environment. I want to be able to detect if the operators have the laser turned on while they are operating, but without disrupting or otherwise interfering with the laser beam. Is there some sort of laser detector that can detect scattered laser light from, lets say, 6 inches away from the actual pencil beam at the target range.

 

Like standing beside the beam and watching for light being scattered by the dust? I guess you could detect the scattered light using a red filter on the detector, but it would be ever so much easier to have confidence if the laser had a frequency besides its wavelength. Much like an infrared remote control modulated at 38 kilohertz, you would watch for the modulation frequency. That would make it definite when you got a, "yes" result.

That's the best guess I have right now.

 

Why not simply monitor/tap into/replace the switch that turns the laser on?
When the laser is turned on then you simply turn on a red "beacon" light or buzzer or whatever you want it to do..
No need to "detect" anything..
KISS

 

I have a compromise idea. Install a beam splitter in the laser and install the detector where the beam splitter will send half the light.

 

Like standing beside the beam and watching for light being scattered by the dust? I guess you could detect the scattered light using a red filter on the detector, but it would be ever so much easier to have confidence if the laser had a frequency besides its wavelength. Much like an infrared remote control modulated at 38 kilohertz, you would watch for the modulation frequency. That would make it definite when you got a, "yes" result.

That's the best guess I have right now.

There isn't any other laser light present so any laser light detected would be from the laser on the tripod.

 

I have a compromise idea. Install a beam splitter in the laser and install the detector where the beam splitter will send half the light.

We considered putting a fan lens on the laser and then having the detector below the target to detect the laser line. This has merit if we can source an appropriate detector.

 

Why not simply monitor/tap into/replace the switch that turns the laser on?
When the laser is turned on then you simply turn on a red "beacon" light or buzzer or whatever you want it to do..
No need to "detect" anything..
KISS

The laser is tripod mounted and remote from any instrumentation so it is not desirable to run a signal cable to it. Thanks for the idea though.

 

Quick test: Aimed laser at wall, inserted clear piece of plastic at 45 deg. no visible drop in wall light spot brightness, but sufficient light at 45 deg.to be detected ( post # 4 ).