>
> On Apr 27, 2010, at 9:38 AM, Herbert Graf wrote:
>
> 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 =3D 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?
>

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=D7 @ 36 Mbit/s (4.5 MByte/s)
2=D7 @ 72 Mbit/s (9 MByte/s)
4=D7 @ 144 Mbit/s (18 MByte/s)
6=D7 @ 216 Mbit/s[1](27 MByte/s)
8=D7 @ 288 Mbit/s (36 MByte/s)
10=D7 @ 360 Mbit/s (45 MByte/s)
12=D7 @ 432 Mbit/s (54 MByte/s)

from  :  http://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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