Electrical – Searching for a suitable method to detect peak heights of nanosecond pulses

Elementary, Watson. You sortof had the idea with #2, except that you don't want a negative gain but rather a gain between 0 and 1. In other words, you want to attenuate the 0-15 V input signal to match the input range of your A/D.

This is easily accomplished with two resistors in a "resistor divider" configuration. If your A/D has a native range of 0-5V, then you want to divide the input voltage by 3. This can be accomplished, for example, with 2K Ohms in series followed by 1K Ohms to ground.

Anything you do to a signal will always change it slightly. In this case, some of the high frequencies will be lost. However, at impedances of 10s of K Ohms, this won't be a problem with a sample rate of 1KHz or less. That implies a upper frequency limit of 500Hz maximum, rather less in practise. Even 100s of K Ohms used in the resistor divider should be able to pass such low frequencies without losing the part you care about.

I'm sceptical that you'll be able to retain the pulse energy information through excessive amounts of low pass filtering. The more you slow down the pulse, the smaller the amplitude will get, and the lower the SNR of your sampling process will be.

As for how to measure this signal remember that the fastest scopes available actually have very low sample rates (on the order of 40 kHz). The trick is to use a fast sample-and-hold or track-and-hold circuit.

For a 1 ns aperture, you should be able to make a T/H circuit with just a few dollars worth of parts for a reasonable price. The challenge will be to syncronize the T/H circuit with your laser pulse. Pretty much any ECL logic family still available will have the timing performance needed for this, but the details of how to do it depend on what signals your laser produces to syncronize with.