Question Concerning Optical Pulse Amplification

[AndyBolt]

Hello Guys

I have just started a project about building a laser ranger, using 1 nano second laser pulses.

We are using a 350nm laser which coresponds to some Tera hertz in frequency. The datasheet for the laser says that the pulse can be expected to be of gaussian type.

My question is: We are then using a avalanche photodiode to detect the pulse, but what frequency spectrum should i design my electronic amplifier for?

If i furrier transform a gaussian pulse, i get yet another gaussian in the frequency spectrum. But what about the center frequency? is it still in the tera hertz area? Or has the photodetection converted the center frequency to be around 0Hz?

I hope some of you guys got experience within this area and can help me out

Thanks on beforehand!

 

[ericgibbs]

hi,
Assuming its a pulsed laser diode project its usual to have the same wavelength receiver.

The Gaussian distribution typically applies to the shape of the radiated energy pulse levels.

Why have you chosen a close to UV wavelength and a 1nSec pulse.? what are you planning to measure.??

You should find this link useful.
**broken link removed**

 

[crutschow]

The general rule is that a 1ns gaussian pulse needs an upper frequency response greater than 0.44/1ns = 440MHz.

 

[AndyBolt]

Hello, thanks for the reply

Sorry i meant 550nm.

So since it is the radiated energy that i observe through the photodiode the frequency spectrum is located around 0Hz with an upper frequency response around the 440MHz. Ok thanks!

Do you know any Bipolar transistors suited for this broadband amplification, with focus on a low noise figure?

I have only worked with narrowband hf amplifications, how do you couter the fact that the transistor changes it Y'parameters over the broad frequency band? Do you calculate an average, or design the amplifier for the Y'parameters at the center of the required frequency band?

 

[ericgibbs]

hi,
Look at the Philips BFG480W transistor.

Can you say what is the planned use of the laser project.??

 

[crutschow]

So since it is the radiated energy that i observe through the photodiode the frequency spectrum is located around 0Hz with an upper frequency response around the 440MHz. Ok thanks!

If you don't need DC response, then your amp doesn't need to go to DC.