This is less than what you would expect, based on the assumption that the frequency contents is determined by the laser pulse duration and that's because it isn't. It's determined by the current which can have a risetime slower that the laser pulse duration. An example of a THz signal measured by us is shown in Fig. 4. Shown are two measurements. The red curve is obtained with zero bias.
Noise level is shown by multiplying the latter curve with a factor of a hundred.
Oscillators, although they generate low power power THz pulses, are much better suited for sensitive detection of THz pulses. The low repetition rate amplified laser, on the other hand, allows one to generate high power THz pulses. Depending on your application either can be suitable. The THz signal shown in figure 4 has some interesting features, not the least of which is that the signal appears to be a half-cycle pulse. That is, it appears to consist of only half a cycle of the electric field.