Detect a laser from250 meter Using Photo diode

[heena123]

hi,

I am using one laser transmiteer hch rotates a 600rpm.635nm Visisble Red Laser Light .Bam width is 3m
I used BPW34 Photo diode .i gave Reverse bias voltage & connect with 4.7kOhm resistor and get o/p pulse from it.

i get pulse up to 100 meters distance with appropriate delta voltage ,means i get proper pulse.

But what i have to do with detect same laser light fro 200meter distance.

Should i go for 6.8 or 6.1k resistor with better o/p. or i have to use a peak detection.

My other problem is how i reduce a light effect on photo diode in morning and evening because of that my o/p voltage goes high more. ialerady used red filter for this .
But not satisfied with it.

Please guide me for this.

Regards,

 

[jiripolivka]

hi,

I am using one laser transmiteer hch rotates a 600rpm.635nm Visisble Red Laser Light .Bam width is 3m
I used BPW34 Photo diode .i gave Reverse bias voltage & connect with 4.7kOhm resistor and get o/p pulse from it.

i get pulse up to 100 meters distance with appropriate delta voltage ,means i get proper pulse.

But what i have to do with detect same laser light fro 200meter distance.

Should i go for 6.8 or 6.1k resistor with better o/p. or i have to use a peak detection.

My other problem is how i reduce a light effect on photo diode in morning and evening because of that my o/p voltage goes high more. ialerady used red filter for this .
But not satisfied with it.

Please guide me for this.




Laser power is often high enough to be detected after being reflected from the Moon. To do it (a long distance), you generally need:

a. optical system ; laser alone may have a divergent beam, so you need a "telescope" to focus it into a narrow beam where you need to detect it.
b. Filtering : visible lasers emit red or green or IR, so your photodiode must have a good filter to reduce the noise from sunlight, etc. An advantage can be if you can modulate laser light by a chopper or chop laser current by ~ 1 kHz. Then a selective amplifier of photodiode signal can reduce other noise by > 30 dB or more
c. optical system (telescope) is good to have at the receive side, too.
d. As you mentioned that you have tried some resistor values for photodiode current, this is also important. Peak detection has a sense if laser light is modulated as in b. above. But you can use a synchronous detector (lock-in) to pull the useful signal from noise, by narrowing the noise bandwidth.

 

[heena123]

hi,

OK i understand,
I have to use a proper filter to filter out other wave which i not required.

Thank You so much for your concern,

Regards,

Heena

 

[FvM]

Due to expectable beam divergence, you get about the same pulse shape at 100 and 250 m (a gaussian pulse of serveral µs width). Intensity will decrease with 1/distance according to the vertical divergence. So it's mainly a signal amplification (and possibly noise level) problem.

The detector bias circuit has to be designed according to DC light requirements, direct sun light in the morning/evening is the worst case scenario as you mentioned. Apparently, the DC sensitivity of your circuit needs to be reduced.

You should think about a high pass and succeeding amplifier. Signal processing design depends on the application requirements and available total measuring time. Ultimately, a lock-in amplifier could synchronize to the rotation frequency.

You didn't mention the application, is it levelling?

Beam width is 3m

???

 

[heena123]

Yeah ,
Its Similar like that...
but for this i already amplifies this signal,But my main hurdle is to filter out this RED Laser of 635nm from particular filter.
Also i used simple Confutation for get it out this signal using simple reverse bias a photo diode.

Regards,

heena

---------- Post added at 11:57 ---------- Previous post was at 11:56 ----------

Yeah ,
Its Similar like that...
but for this i already amplifies this signal,But my main hurdle is to filter out this RED Laser of 635nm from particular filter.

Because my photo diode work/sense from 300nm to 1100nm wavelegth. But in mornig and in evening it 's very hard to detect this signal and filter it out from the sun Ray's.

Also i used simple Confutation for get it out this signal using simple reverse bias a photo diode.

Regards,

heena

 

[FvM]

You preferably would want to use a small band interference filter. Professional laser leveling equipment I know is using it.

 

[hiren.dave@bhuved.com]

hi fvM..

thanks for your support. which kind of small band interference filter we have to use ? how to use it ?

 

[keith1200rs]

One of these:

You need to ensure that the filter is not too narrow for the laser. The laser wavelength will drift with temperature and some are not single mode so emit more than one wavelength (although usually when driven hard most of the power is in the dominant wavelength).

Keith.

 

[FvM]

You need to ensure that the filter is not too narrow for the laser.

Yes. The filter should possibly take account for different red laser wavelengths used with the receiver. On the other side, residual ambient light sensitivity is proportional to bandwidth. 20 to 40 nm bandwidth (FWHM) may be appropriate.