Recent content by mathew@upb

The lock-in has both current and voltage inputs. The signal to be measured could not be detected by using the voltage input, but could be detected with a passive VI converter (a resistor) by using the current input. I hope, by a suitably designed VI converter the S/N can be improved further...

I want to measure optical power levels at tens of fW power level. What you suggested is the best way to do this. However, I do not have the instrumentation (monochromator with the required spectral resolution) to do this readily available. What I have is an optical spectrum analyser which...

>>Are you able to take a first cut at the resistor values on your own? Not yet. Any help would be appreciated. What are the selection criteria? Thank you very much for the enlightening inputs. I see that the solution is not that simple as I thought it to be.

The lock-in accepts both AC as well as DC inputs. In this case I guess, the DC input is preferred as the signal to be measured does not go below zero. I have not understood the second question. Are you referring to the lock-in's current input? If yes, it is less than 250 k (@ 100 Hz).

Thanks! few tens of pA also would be okay. Anything larger might saturate the lock-in's input. Exactly. It is noisy. I hope to improve S/N by the lock-in. I have already tried passive V->I conversion (with a resistor) and it seems to work better (with a test optical signal at a larger...

The 'photodiode' has a built in transimpedance amplifier which does the I->V conversion. Bandwidth should be less than 300 Hz.

Can someone advice how a V to I converter (with IC741 or any other easily available Op Amps) can be made for converting few mV to pA. The converter is to be used to convert the output from a photo-diode preamplifier to a lock-in amplifier with current input. Thank you for the help, in advance.