超快光学--第02章-概述.pptVIP

* * * * * Slide used with permission from Dan Mittleman * * http://resource.isvr.soton.ac.uk/spcg/tutorial/tutorial/Tutorial_files/Web-further-dispersive.htm * * * * * * * * * * Ytterbium Tungstate (Yb:KGW) Model t-Pulse 20 t-Pulse 100 t-Pulse 200 Pulse energy (nJ) 20 100 200 Average power (W) 1 1 2 Repetition rate (MHz) 50 10 10 Ytterbium doped laser materials can be directly diode-pumped (at 980 nm), eliminating the need for an intermediate (green) pump laser used in Ti:Sapphire lasers. They lase from 1023 to 1060 nm. They also offer other attractive properties, such as a very high thermal efficiency and high average power. Amplitude Systemes Active mode-locking Any amplitude modulator can induce losses for times other than that of the intended pulse peak. It can be used to start a Ti:Sapphire laser mode-locking. Modulating the gain rapidly—gain switching—is essentially the same as active mode-locking. Gain switching commonly mode-locks semiconductor lasers. Synchronous pumping Pumping the gain medium with a train of already short pulses yields a train of even shorter pulses. Trains of 60 ps pulses from a Nd:YAG laser can yield 1 ps pulses from a sync-pumped dye laser. Pump beam Gain medium Saturable absorber Short pulses (ps) The laser round-trip time must precisely match that of the train of pump pulses! Hybrid mode-locking Hybrid mode-locking is any type of mode-locking incorporating two or more techniques simultaneously. Sync-pumping and passive mode-locking Active and passive mode-locking However, using two lousy methods together doesn’t really work all that much better than one good method. * * Erich Ippen, MIT * * * * * * * * * * Didomenico, J. Appl. Phys. 35, 2870 (1964). Hargrove, et al., Appl. Phys. Lett., 5, 4 (1964). * * * * * * * * * * * * * * * * A generic ultrashort-pulse laser A generic ultrafast laser has a broadband gain medium, a pulse-shortening device, and two mirrors (among other stuff): Many pulse-shortening devices h