Argon actively mode-locked

Fig. 5. High repetition rate pulsed excitation systems for picosecond absorption and emission studies, (a) Pulsed e -beam with Cerenkov or laser probe pulses (b) actively mode-locked, synchronously pumped argon ion jet stream dye laser. See text for further details.

For the one-color picosecond pump probe experiments (see Sect. 3.2.2), an astigmatically compensated dye laser (Spectra Physics model 375) with rhodamine 6G/rhodamine B is used [190]. The dye laser is synchronously pumped by an actively mode-locked argon ion laser (Spectra Physics model 171). In the synchronous pumping process, the output pulses of the mode-locked ion laser are used to excite the dye laser, whose cavity length has been extended to be equal to the ion laser s cavity 1.8 m) [187]. The transmission of the dye laser s output coupler is 22%. With this setup the emitted dye laser pulses have a pulse duration of 1.38 ps and a bandwidth of 40 cm (see Fig. 2.3). The pulse repetition rate is 82.5 MHz and an average power of 120 mW is obtained over the tuning from 600 nm to 630 nm. 

Fig.11.6a,b. Observed output pulses from an argon laser at X = 488 nm, actively mode locked by an acousto-optic modulator, (a) Detected with a fast photodiode and a sampling oscilloscope, (b) detected by single-photon counting technique using a photomultiplier. The oscillations following the optical pulse in (a) are due to cable reflections of the electric output signal from the diode. The pulse width in (b) is limited by electron transit time variations in the photomultiplier [11.10]... 

When a cw laser is mode locked its average output power decreases by a factor 3 which depends on various parameters of the active medium, such as the lifetime of the upper laser level. For mode-locked argon lasers 3 is about 2-4. The peak power, however, is increased by a factor 6v/(3Av). 

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