Pump mode generation

Picosecond pulses can be produced in a number of different types of laser systems. As an example, a brief description is first given of a synchronously pumped c.w. dye laser such as can be readily assembled from commercially available units. Generation of repetitive subnanosecond pulses in a c.w. laser by mode-locked synchronous pumping was first described by Harris et al. [12]. The essential features of such a system are shown in Fig. 3. In this system, an acousto-optically mode-locked ion laser is used to pump the dye laser. In order to achieve synchronous pumping, the length of the dye cavity must be adjusted so that the dye laser intermode spacing is an integral multiple of the pump mode-locker frequency. 

The results have been recently obtained by Olsen et al. [38], and they show that even for almost vanishingly small e, which is inversely proportional to the initial mean value of the number of the pump mode photons, usually very large, the quantum fluctuations have huge macroscopic effect on the system dynamics. It is evident that the quantum noise, which is always present, is responsible for the oscillations between the two regimes of second-harmonic generation and downconversion. The period of oscillation is becoming infinite as e vanishes. 

Experimental studies of features of the alloy-structure interaction were carried out by tests of mock-ups, models and real primary components. Fuel subassemblies, control and safety system components, primary pumps, steam generators, sections of main and auxiliary pipelines and their valves have been tested. In the course of tests requirements have been worked out for the temperature conditions of heating up and cooling down modes, as well as for separate structures designed for avoiding damages at multiple condition changes. 

J. Kiihl, H. Klingenberg, D. von der Linde, Picosecond and subpicosecond pulse generation in synchroneously pumped mode-locked CW dye lasers. Appl. Phys. 18,279 (1979)... 

P.K. Benicewicz, J.P. Roberts, A.J. Taylor, Generation of 39 fs pulses and 815 nm with a synchronously pumped mode-locked dye laser. Opt. Lett. 16, 925 (1991)... 

For excitation and detection of fine structure beats with a frequency of 517 GHz subpicosecond light pulses are necessary. For this purpose we used a synchronously pumped mode-locked dye laser with saturable absorber in the dye solution. The dye laser generates light pulses of about ItOO fs duration at a pulse rate of 8U MHz. It is pumped by a frequency doubled actively mode-locked Nd YAG laser and tuned to a wavelength of 589.3 nm for resonant excitation of the Na atoms into the 3p fine structure states. 

The experimental set-up we used is shown in Fig. 2, A synchronously pumped mode-locked and cavity-dvunped dye laser, which can be timed to the D or Dj line of Cs, generates pulses of about 20 ps duration at a pulse rate of U MHz and peak powers of several hundred watt. They are split into linearly polarized pump pulses and stronger circularly polarized probe pulses, which pass an optical delay line. Both beams are focussed into a common interaction region where they act on the Cs vapor, which is contained in a cell at room temperature. The radiated wave propagating in pump pulse direction is detected by a photomultiplier, which measures the transmitted average intensity behind a crossed polarizer as a function of the delay time. 

Synchronously Pumped Mode-Locked Dye Laser. Organic dyes have proven to possess excellent properties for the generation of ultrashort laser pulses. Numerous approaches have been taken to the mode-locking of a dye laser, including both active and passive techniques. As a result, tunable continuous wave (cw) dye lasers have been successfully mode-locked over the past 25 years [183, 184], and pulse widths on picosecond and femtosecond timescales have been reported by many groups. 

There is a potential for unstable flow through pumps, which is created by both the design-flow pattern and the radial deflection caused by back-pressure in the discharge piping. Pumps tend to operate at their second-mode shape or deflection pattern. This mode of operation generates a unique vibration frequency at the second harmonic (2x) of running speed. In extreme cases, the shaft may be deflected further and operate in its third (3x) mode shape. Therefore, both of these frequencies should be monitored. 

Sum-frequency mixing of two solid-state YAG lasers in a nonlinear crystal (see Ch. 20) to generate 589 nm in CW, CW mode-locked and macromicro pulse formats. The Nd YAG lasers can be pumped by flashlamps, but higher efficiency is obtained using diode lasers. 

Linearly polarized, near-diffraction-hmited, mode-locked 1319 and 1064 nm pulse trains are generated in separate dual-head, diode-pumped resonators. Each 2-rod resonator incorporates fiber-coupled diode lasers to end-pump the rods, and features intracavity birefringence compensation. The pulses are stabilized to a 1 GHz bandwidth. Timing jitter is actively controlled to < 150 ps. Models indicate that for the mode-locked pulses, relative timing jitter of 200 ps between the lasers causes <5% reduction in SFG conversion efficiency. 

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