IR LiDAR

[DiAlSiC]

Is it possible to retrofit a reflector type telescope to collect an IR laser scatter signal of a dust cloud ?

 

[IRstuff]

Depends on what exactly you are trying to do. Lidar, or LADAR, since you refer to a laser, requires something that discriminates time, not just intensity. This means that you need a detector that can either be time triggered (range-gated) or can actually measure elapsed time.

Beyond that, why would you think a reflector optic is different than refractive?

TTFN

FAQ731-376

 

[DiAlSiC]

The dust cloud I am trying to measure is in a relatively close proximity so I thought a larger diameter telescope would have a better chance at collecting the incoming signal.

My Objective is to measure the degree of Aerosolization of the dust cloud ( how long it will stay suspended in air after its being kicked up. so I suppose I am trying to measure the intensity of the reflected laser of the dust particles over a time period.

 

[drawoh]

DiAlSiC,

I work for a company that builds LIDAR systems that measure pollution and dust clouds. You can use a telescope, reflector or otherwise, to capture laser energy reflected from your cloud. This requires all sorts of electronics and software, depending on what information you are trying to capture.

As far as retrofitting, it depends on the telescope, and whatever it is you are trying to retrofit it to.

What are you trying to do, capture more light?

JHG

 

[DiAlSiC]

As far as electronics and software go, edmonds optics have a very nice IR lasers and detectors along side a free software that comes with it.

the information I am trying to gather are quite straightforward provided that the optical part is working properly.
- point the laser and the LiDAR at the center of the cloud and measure the reflected laser power over a period of time which could be done easily using a labview program where you measure output laser power through a beam splitter and compare it to reflected laser power.
or maybe just measure the reflected laser power alone would do the trick if I just want to measure the relative reflectivity between time laps.

- as far as the telescope, I may need an optical lens that pass only coherent light ( not sure if it exist) to minimize ambient noise.

 

[IRstuff]

Are you going to do this in the daytime? How are you going to minimize sunlight interference? Is the laser pulsed? Is the laser beam expanded? Are you concerned about the size of the beam relative to the mean free space between particles.

Perhaps a transmissometer might be more appropriate:

http://www.vaisala.com/weather/products/fs11.html

TTFN

FAQ731-376

 

[lumenharold]

I could assume that you are aware but just to be sure...

The NIR lasers that I saw at EO on a quick check were all Class IIIb. You have a laser safety officer or a qualified person that is aware of the safety issues with NIR lasers, correct? Not much of that cohernet NIR energy is going to be scattered by a dust cloud unless the particles are really dense and the cloud is big or has a brick wall behind it. Are you passing the laser through the telescope to expand the beam as well? That wouldn't be so bad then. Energy density calculations would still need to be done if the cloud is outdoors.

I'll appologize in advance if you are aware but not everybody is.

Harold
SW2009 SP4.0 OPW2009 SP2 Win XP Pro 2002 SP3
Dell 690, Xeon 5160 @3.00GHz, 3.25GB RAM
nVidia Quadro FX4600

http://www.lumenflow.com

 

[drawoh]

...
- as far as the telescope, I may need an optical lens that pass only coherent light ( not sure if it exist) to minimize ambient noise.

Narrow band interference filters are commonly used on LiDAR detectors. There is usually no point in looking at anything not close to the laser's wavelength.

Just to reinforce lumenharold's point a bit, all the cloud mapping LiDARs I am aware of use Class[ ]IV lasers.

JHG

 

[DiAlSiC]

- I read somewhere about eye safe LiDar System so I assumed that its using a safe laser. I certainly do not want this project to cost too much on any level.

- my understanding is that powerful lasers are used with LiDAR because of the great distances involved (clouds, Mapping ,ect. in my case I am using it for a short distance measurement.
- the experimental area is no larger than a tennis court. a standard 100mw laser would seam sufficient however I am not sure if I would be able to collect any of the signals back.
- the dust I am working with is IR reflective, to answer some of the concerns from previous postings. I would rather work with a red laser if it will yield any preliminary data.

- So the conclusion to a previous question is that there is no such a thing as non-coherent light filter lens.

 

[IRstuff]

No, the issue is that most lasers put out a very tiny beam, and the majority of the energy will most likely miss the particles altogether unless you have an extremely dense or thick plume. The energy and particulate depth density determine the dynamic range of your measurement. Nonetheless, unless you have a spatially large beam, say on the order of 4 inches in diameter, you're likely to get extremely noisy measurements, since you would be doing point measurements instead getting average measurements.

TTFN

FAQ731-376