1. Gone in a Picosecond

2. Picosecond Sources
Laser-Based Techniques

3. A femtosecond is equal to 10−15  of a second.
A picosecond is equal to 10−12 of a second.
In these sources, picosecond pulses are used.
Picosecond pulses are traditionally generated with a femtosecond laser and a photo-conductive antenna (PCA).

4. DC voltage is applied to both electrodes of PCA.
Elektric field occurs on semiconductor.
Ultrashort optic pulses create electrons and holes.
Generate currrent
The small transition region and the short transport time
Generate subpicosecond pulses.

7. Conventional THz-TDS systems use a single source and detector.
Motion is required to obtain the image.
A mechanical delay line is required to obtain all the pulses.

8. A mechanical delay line is slow.
An alternative solution to the mechanical delay line is a two-laser system with frequency shift.
A laserless, fully electronic approach is required to generate picosecond pulses.