photodetector amplifier - help needed

[karesz]

photodetector amplifier

Yea, thes is normal, then self most IT laser has some red light spectra too...
You must find a position & distance from your detector with maximum of signal, than fix it!
It will be better to apply a pigtail for so a measurement, then otherwise you will have to much changings/effects in your meas- setup, you will stangig to debag some dejustages...
K.

Added after 2 minutes:

You must be careful with Laser light/power_your eyes are irreparable! Is it a IR Laser or visible?

 

[harryd]

photodetector amplifier

it is one of the those 5mW laser pointers.

ok last question what measurments should i consider to see if i need a gain or not ?

when i put the detector on a table and apply the laser on it ( from distance ), it reads around 3- 3.5 volt. is that enough to be clear on the oscliscope or do i need an amplifier ??

note : if i try to put the fiber in betweeen and put the detector right infront of one end and the laser at the other end, should i get the same value ??

 

[karesz]

photodetector amplifier

You see,
Your oscilloscope has a range switch/sensitivity selector of min. 5mV/Div, but often 2 or 1 mV/div...
For a full screen (hight) you need then 5x5=25mV signal, you have minimum 3V, also more as enough for most sensitive range
You can set it to 200 or ev. 500mV/div, the (as I wrote it over their) you will have to calculate with (for us unknowed) couplings inefficiency!
Its real possible, that your signal will be only in 10th of % or maybe only some percents of direct detected beam into fiber coupled system...
As Keith told too; you must try it_do experimenting...
K.

 

[harryd]

photodetector amplifier

so i am in the clear?

Added after 1 minutes:

and when i use the fiber, i can still get readings on the oscilloscope ? so i dont need an amplifier?

 

[karesz]

photodetector amplifier

You see, if your direct detection is at 3V, maybe you will become only 10% of that-> your signal is at 300mV, for a scope full hight display you dont need an amplifier!
BUT DONT forget pls; all these number are only ASSUMED yet, but not irreal!...
K.

 

[harryd]

photodetector amplifier

so basically the coupling efficiency will tell whether i need an amplifier or not

 

[karesz]

photodetector amplifier

So is it!

Otherwise; you can search a little for Beam profile meters/meas.-techniques...
Usual is not the full beam "to see" with a detector, but only over a small slot...
So will you have more sharp profiles.
OK, I must goo to sleep_we have 2 Oclock!! sorry!
By!

 

[harryd]

photodetector amplifier

thanks alot man u really helped me
god bless you
ok to calculate the coupling efficiency i have to do some by trial and error ?

and what is the threshold for an acceptable coupling efficiency?

 

[karesz]

photodetector amplifier

Threshold is setting only from your sensitivity/scope & other instruments...