How are lasers used for measuring distances and other quantities?

[fifi]

Hi! I have to make a presentation about the usage of lasers in measurements, but I am not sure what I should include. I thought of something like using laser beams for measuring distances, but I don't know how exactly this can be done and what else can be measured with lasers. I'd be greatful if you could help me

 

[HallsofIvy]

My suggestion is that you go to google.com and enter "laser distance theory" or something similar (without the "theory" you get a lot sites of companies that manufacture lasers).
I did and got this interesting site:
http://www.sfgate.com/cgi-bin/article.cgifile=/chronicle/archive/2002/01/17/MN81755.DTL

 

[brewnog]

You obviously realize that there are lots of uses for lasers in measurement, but I think I have a particularly interesting application. I'm bound not to tell you too much about it, but I'm sure that if you thought about it then you'd be able to fill in the blanks.

Some researchers I know are currently using lasers to measure the speed of air in a hypersonic wind tunnel around an object which is designed fly through the air very, very quickly (~Mach 15, of the top of my head). A pretty powerful Class IV CO2 laser is split up into two parallel beams. I'm not too sure of the arrangement, (because I haven't been allowed to play with it..!), but using a system of mirrors/prisms one of these beams gets routed through the hypersonic air flow, and the other flows through stagnant air. The path lengths of the two beams is identical. The beams then meet up again, and the spacing of the resulting interference fringes (as recorded on some photographic film) is used to determine the speed of the moving air.

 

[PerennialII]

Yeah, googling for laser interferometry will bring up quite a number of applications from different fields in addition to the distance, displacement etc. measurements. We've used the thing for example in analysis of material damage & cracking in 3D ... gives you awesome resolution.

... about some of the principles in a tolerably interesting application :

http://www.ndt.net/article/v04n12/palles2/palles2.htm

 

[fifi]

Thanks a lot! I really needed examples of what can be measured by lasers.
I have one more question. Do you know how laser triangulation works for mesuring distances? As far as I could understand from what I read, the laser beam is reflected by the target and then the target is projected on a detector by a lens. But how can we measure the distance to the target in this way?

 

[Claude Bile]

It is probably worth doing a quick search on LIDAR systems as well.

Also, lots of commercial sites have basic information on the basic principles of operation of their products.

Claude.