Active Mode Locking

The modulator is often placed near an end of the resonator.

Active mode locking. Active mode locking in an actively mode locked laser as shown below mode locking is achieved with a modulator for example electro optic type which modulates the resonator losses in exact synchronism with the resonator round trips. Mode locking ist die synchronisation der im laser schwingenden eigenzustände zur erzeugung von extrem kurzen lichtpulsen bis in den femtosekunden bereich der begriff modenkopplung bezieht sich darauf dass bei einer möglichst großen anzahl von moden eine konstante phasenbeziehung zueinander angestrebt wird. In a pockels cell even though this leads to chirped pulses this technique is called fm mode locking fm frequency modulation although the term phase modulation mode locking would seem to be more appropriate. Chapter 5 active mode locking forsimplicity we assume that the laser operates inthe transverse fundamen tal modes and therefore we only have to treat the longitudinal modes of the laser similar to a simple plane parallel fabry perot resonator figure.

In an actively mode locked laser as shown below mode locking is achieved with a modulator for example electro optic type which modulates the resonator losses in exact synchronism with the resonator round trips. We consider one polarization of the field only however as we will say later for some mode locked laser polarization dynamics will. The shorter the circulating pulse becomes the faster is the loss modulation obtained. Die einzelnen moden sind dann phasengekoppelt.

The circulating pulse goes through the modulator at times where the losses are smallest and the. This holds at least for the. Nevertheless this regime is useful for many laser systems including powerful ones where strict synchronization with external periodic signal is needed. Somewhat less obviously active mode locking also works with a periodic phase modulation instead of amplitude modulation e g.

30 years passed since d. Siegman k s developed their present. Some fm mode locked lasers exhibit an instability. The circulating pulse goes through the modulator at times where the losses are smallest and the.

Mode locking is a technique in optics by which a laser can be made to produce pulses of light of extremely short duration on the order of picoseconds 10 12 s or femtoseconds 10 15 s. A laser operated in this way is sometimes referred to as a femtosecond laser for example in modern refractive surgery the basis of the technique is to induce a fixed phase relationship between the. Active mode locking itself provides pulses not shorter than picoseconds. The modulator is often placed near an end of the resonator.