Basic Amp for Laser

Discussion in 'General Electronics Chat' started by mchl_hemingway, Mar 25, 2014.

  1. mchl_hemingway

    Thread Starter New Member

    Mar 16, 2013
    Hi All,

    I was hoping you fine people could point me in the right direction with my circuit. I'm trying to drive a Quantum cascade laser (QCL) with a periodic current pulse (about 175Mhz). I have a 3Ghz signal generator which I plan to use to set the frequency. What I'm trying to do is take the sinusoidal input from the sig gen and use it to signal a current pulse. I suppose the devils in the details of the laser. As the better read of you may know QCLs are very much non ohmic. Our device has a knee on the I-V curve at about 10-12V (then band alignment occurs and resonant tunnelling begins). The most current needed in the pulses is about 200mA which would occur just after the knee, around 12V. The diagram shows my first idea of how to do this but I think I need help before etching another board. Ultimately I could go a few labs down the corridor and pick up a good unit that will do this job but I'm trying to develop my electronics and want to get this nailed down.

    For now the current pulse doesn't need to be perfectly shaped, though in future the general trend will be to reduce the pulse width. In the diagram you will see that 2 RF BJTs are in parallel, this has been to provide enough collector current, I know this to be generally a bad idea. Also the JFET is to provide the high input impedance needed for the signal gen. It was my half understanding that this scheme (JFET driving BJTs) would allow a non ohmic load to be driven to the required current. The power coming from a lab bench supply which would be set a few volts above that required to drive the laser at the required peak current.

    Any help at all would be great. I'm sure I've not been as clear as is possible but if any more details are required, I'll happily try harder.:)