optical measurement with photodiode

[kum111]

hello ,

I am trying to bulid a system for optical measurement of laser radiation , for laser light measurement i have selected a si pin photodiode. need information about the circuits which can measure the current ot voltage from photodiode , am very new to this field . any ideas or links will be helpful. thank you all

 

[thylacine1975]

Hiya kum111, what sort of laser/optical measurement? Are you interested in intensity, spectral information, single photon counting or phase/amplitude quadrature homodyne measurements? Are you studying pulsed/CW systems? Also, what speed do you need? People chasing gravity waves get excited about the DC end of the spectrum, while communications people prefer the microwave end

For a good overview of relevant detector circuits, I've heard good things about (but never personally read) The Fundamentals of Photonics (https://www.amazon.com/Fundamentals...UTF8&qid=1361397007&sr=8-1&keywords=photonics).

Phil Hobbs (https://www.electrooptical.net/) has written a good series of articles on low noise optical detection worth a look too.

There's been lots of chatter in this forum about photodetectors - try a few searches. Alternatively, I posted a really simple photodiode based intensity detector a while back - check out post #23 of this thread: https://www.edaboard.com/threads/229306/.

If you post a few more specifics about your requirements I might be able to point you towards something more relevant to your needs - cheers

 

[kum111]

hello thylacine ,

Thanks for the information . I have to detect laser pulse radiation in this project, am interested in intensity of laser with high speed , pulse shaped and laser beam power at different distance from it . This laser has 70mm width and 20mm height ,have to measure energy intensity, laser beam power at different points on this 70 , 30 mm length.

 

[thylacine1975]

So... are you *profiling* the intensity distribution of the beam? If so - what spatial resolution is required across your 70mm/30mm window? The reason I ask is that things are much simpler if you can use a diode with an active area (and therefore dimension) ~the required resolution and avoid the use of external focussing optics. Do you need to create an XY stage to step the measurement diode across the measurement plane as well?

Also, what constitutes "high speed"? If you're just interested in an average intensity distribution, then any old (few-Hz bandwidth) diode/transimpedance amplifier will probably do the trick for you. On the other hand though, if you want to observe the time dependance of the intensity of the (pulsed?) laser, you might need a *seriously fast* (and expensive/multi GHz league) measurement setup... how 'fast' do you need to go?

 

[kum111]

hello thylacine ,

sorry for the late reply , first of all i did not understand your question about spatial resolution , about the laser pulse and speed , am using a laser which has a pulse of 1microsecond , so i have to detect this pulse start . which am able to do with a si photodiode with a resistor(1k) in parallel but not with sum reverse voltage . any ideal or circuits about how to make it work in reverse bias .

 

[thylacine1975]

Ah no problem, I was just curious about the application of your photodetector and the practical constraints that may have come with it

Back to the detector though - no problem! 1us laser pulses are slow enough/low frequency that you have a wealth of easy to construct options available to you, as the required bandwidth of your detector is only a few MHz. As such, pretty much any silicon diode with an active area < your average solar cell will have a low enough junction capacitance to serve as a suitable sensor. To see some examples of how to apply your photodiode in the reverse biassed configuration, have a look at the references I posted earlier - particularly and the multiple designs published at: http://www.0x00f.com/files/appnotes/photodetctor-designs.pdf

 

[kum111]

at present am using only a simple receiver photodiode and a load resistor . as the photodiode has sum capacitance and this load resistor from RC constant i wanted to control the 1 microsecond with this , it works pretty good with 1kohm resistor with reverse bias voltage . not able to achieve linearity the time of the output wave changes at the center laser which means more intensity , any ideas

 

[kum111]

can anyone tell me how to make a integrator cricuit for photodiode detector

 

[thylacine1975]

What do you want to integrate? (As in time constant/application?)
The last page of www.hamamatsu.com/resources/pdf/ssd/si_pd_circuit_e.pdf features a resettable analogue photodiode integrator.