I recently made a ultrasound board in order to generate a 80 volts pulse injected to a ultrasound reflective probe. Then I short circuited the response in order to avoid that the pulse entered the amplifier and then I read the response. As you can see at the plot the introduced pulse is very short (about 40ns).

I used it to measure thick of a 1cm sample and then a 2cm sample. The response frequency is the same.

What I have to do to avoid the oscillation? Why I can not read a clear pulse after a time shift?

In attached plots, the blue line is the injected pulse and the red one corresponds to amplified output

https://plus.google.com/u/0/photos?tab=mq#photos/117726452418200192849/albums/5987603245347455857/5987603248200644306?pid=5987603248200644306&oid=117726452418200192849