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'[TECH] : two ways to skin a cat ( or laser sensor '
2010\04\25@183006 by YES NOPE9

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I want to point a laser at a surface that may vibrating at a high  
frequency.
Possibly up to 20MHz.  I want to measure the deflected signal with a  
photodiode.

I have found fast photodiodes ( rise time = 6 nsec ) in the 800 nm  
range for $10 USD.
I want to be able to see the beam so that I can tell if the  
arrangement is aimed correctly.

EITHER
I can somehow  marry a visible beam with the 800 nm beam  ( I don't  
know how )
OR
I can find a fast photodiode ( < 10 nsec , under $20 ) that senses  
light in the visible range.


Any suggestions ?

Gus

2010\04\25@184552 by Michael Watterson

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YES NOPE9 wrote:
> I want to point a laser at a surface that may vibrating at a high  
> frequency.
> Possibly up to 20MHz.  I want to measure the deflected signal with a  
> photodiode.
>
> I have found fast photodiodes ( rise time = 6 nsec ) in the 800 nm  
> range for $10 USD.
>  
It probably works just as fast but with less sensitivity for red light
> I want to be able to see the beam so that I can tell if the  
> arrangement is aimed correctly.
>
> EITHER
> I can somehow  marry a visible beam with the 800 nm beam  ( I don't  
> know how )
>  
cut off a piece of  halogen lamp "dichroic" reflector. It reflects
visible and passes IR. Use it to combine the beams?
http://en.wikipedia.org/wiki/Dichroic_filter
> OR
> I can find a fast photodiode ( < 10 nsec , under $20 ) that senses  
> light in the visible range.
>  

I use my camera phone to check IR LEDs

A low light mono security camera works even better to see IR light.

2010\04\26@060938 by sergio masci

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On Sun, 25 Apr 2010, YES NOPE9 wrote:

{Quote hidden}

If you dont need to see the beam all the time, look for something that
will flourece in the visible spectrum when illuminated with 800nm light
(e.g. dye, glass, plastic).

Regards
sergio Masci

2010\04\26@073131 by Michael Rigby-Jones

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> -----Original Message-----
> From: spam_OUTpiclist-bouncesTakeThisOuTspammit.edu [.....piclist-bouncesKILLspamspam@spam@mit.edu] On
Behalf
{Quote hidden}

Depending on laser power, beam spread etc. you might be able to use one
of the IR laser 'cards' that convert IR light to visible light.  We use
these for aligning lasers on optical benches. e.g.

http://www.cnilaser.com/infrared%20viewer.htm


Also have you checked the responsivity of the IR photodiodes at visible
wavelengths?  They might still be useable with reduced output.

Regards

Mike

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2010\04\26@082931 by Alan B Pearce

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> Depending on laser power, beam spread etc. you might be able to use one
> of the IR laser 'cards' that convert IR light to visible light.  We use
> these for aligning lasers on optical benches. e.g.
>
> http://www.cnilaser.com/infrared%20viewer.htm

I have a device similar to that, made by Kodak, which consists of a 1/2"
wide strip of FR4 with a gob of some form of epoxy on the end. Pointing a
device like a TV remote at it makes the epoxy flash in time to the
transmitted IR. I must find a focused IR source and see if it will make a
point of light as illustrated on that page.

I cannot remember what the original Kodak product was that caused them to
make these IR sensors, but a colleague had a bunch of the sensors, and
handed them around at one stage.

2010\04\27@114024 by Herbert Graf

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On Sun, 2010-04-25 at 16:30 -0600, YES NOPE9 wrote:
> I want to point a laser at a surface that may vibrating at a high  
> frequency.
> Possibly up to 20MHz.  I want to measure the deflected signal with a  
> photodiode.
>
> I have found fast photodiodes ( rise time = 6 nsec ) in the 800 nm  
> range for $10 USD.
> I want to be able to see the beam so that I can tell if the  
> arrangement is aimed correctly.
>
> EITHER
> I can somehow  marry a visible beam with the 800 nm beam  ( I don't  
> know how )
> OR
> I can find a fast photodiode ( < 10 nsec , under $20 ) that senses  
> light in the visible range.

DVD players?

TTYL

2010\04\27@161950 by YES NOPE9

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{Quote hidden}

Good idea  ( thank you HG )

from : http://en.wikipedia.org/wiki/Blu-ray_Disc
The specs for a BlueRay device are :
405 nm laser:
1× @ 36 Mbit/s (4.5 MByte/s)
2× @ 72 Mbit/s (9 MByte/s)
4× @ 144 Mbit/s (18 MByte/s)
6× @ 216 Mbit/s[1](27 MByte/s)
8× @ 288 Mbit/s (36 MByte/s)
10× @ 360 Mbit/s (45 MByte/s)
12× @ 432 Mbit/s (54 MByte/s)

from  :  en.wikipedia.org/wiki/Optical_disc_drive
CDs have a base speed of 150KiB/s
For DVD base speed, or "1x speed", is 1.385 MB/s, equal to 1.32 MiB/s,  
approximately 9 times faster than CD's base speed. For Blu-ray drive  
base speed is 6.74 MB/s, equal to 6.43 MiB/s.
Initially, CD lasers with a wavelength of 780 nm were used, being  
within infrared range. For DVDs, the wavelength was reduced to 650 nm  
(red color), and the wavelength for Blu-Ray Disc was reduced to 405 nm  
(violet color).

24x DVD drives seem to be common , so I am going to assume that  
represents a data rate of 33.24MB/sec [ 265.92Mb/sec ]
Do PLs agree ?
Gus

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