Mode colliding-pulse

As one important example, the introduction of the prism-controlled, colliding-pulse, mode-locked (CPM) dye laser [12,13] led almost innnediately to developments in measurement teclmique with pulses of less than 100... 

Several laser systems have been used in our time-resolved PM measurements. For the ultrafast measurements, a colliding pulse mode-locked (CPM) dye laser was employed [11]. Its characteristic pulsewidth is about 70 fs, however, its wavelength is fixed at 625 nin (or 2.0 cV). For ps measurements at various wavelengths two synchronously pumped dye lasers were used (12], Although their time resolution was not belter than 5 ps, they allowed us to probe in the probe photon energy range from 1.25 cV to 2.2 cV. In addition, a color center laser... 

To carry out a spectroscopy, that is the structural and dynamical determination, of elementary processes in real time at a molecular level necessitates the application of laser pulses with durations of tens, or at most hundreds, of femtoseconds to resolve in time the molecular motions. Sub-100 fs laser pulses were realised for the first time from a colliding-pulse mode-locked dye laser in the early 1980s at AT T Bell Laboratories by Shank and coworkers by 1987 these researchers had succeeded in producing record-breaking pulses as short as 6fs by optical pulse compression of the output of mode-locked dye laser. In the decade since 1987 there has only been a slight improvement in the minimum possible pulse width, but there have been truly major developments in the ease of generating and characterising ultrashort laser pulses. 

The advent of ultrafast pump-probe laser techniques62 and their marriage with the TOF method also enables study of internal ion-molecule reactions in clus-ters.21,63-69 The apparatus used in our experiments is a reflectron TOF mass spectrometer coupled with a femtosecond laser system. An overview of the laser system is shown in Figure 4. Femtosecond laser pulses are generated by a colliding pulse mode-locked (CPM) ring dye laser. The cavity consists of a gain jet, a... 

Figure 4. A schematic of the colliding pulse mode-locked femtosecond laser system. Taken with permission from ref. 65.

The earliest subpicosecond systems incorporated dye laser technology. Shank, Ippen, and their colleagues at the Bell Laboratories [34] were the first to develop mode-locked subpicosecond lasers and to show how to compress pulses to very short values. With the colliding-pulse mode-locked (CPM) laser they achieved reduced pulse widths well into a subpicosecond range. Two approaches based on synchronously pumped dye lasers and colliding pulse dye lasers are commonly employed to produce subpicosecond pulses. These are briefly discussed below. 

Fig. 4 Femtosecond dye laser consisting of a colliding pulse mode-locked ring laser (lower level) and a dye amplifier (upper level)...

Colliding pulse mode locking CPM Passive mode locking and eventual synchronous pumping Ring dye laser <100 fs 1 nJ... 

At a proper choice of the amplifying gain and the absorption losses, this situation will automatically be realized in the passively mode-locked ring dye laser. It leads to an energetically favorable stable operation, which is called colliding-pulse mode (CPM) locking, and the whole system is termed a CPM laser. This mode of operation results in particularly short pulses down to 50 fs. There are several reasons for this pulse shortening ... 

M.C. Nuss, R. Leonhardt, W. Zinth, Stable operation of a synchronously pumped colliding pulse mode-locking ting dye laser. Opt. Lett. 10, 16 (1985)... 

D. Kiihlke Calculation of the colliding pulse mode locking in CW dye ring lasers. IEEE J. QE-19, 526 (1983)... 

O. 1 ps by colliding pulse mode locking. Appl. Phys. Lett. 38, 671 (1981)... 

K. Naganuma, K. Mogi 50 fs pulse generation directly from a colliding-pulse mode-locked Ti sapphire laser using an antiresonant ring mirror. Opt. Lett. 16, 738 (1991)... 

The shortest dye laser pulses were first obtained by Fork et al. [12]. Placing a combined prism and diffraction grating sequence into the cavity of their colliding-pulse mode-locked (CPM) dye laser, they could provide quadratic and cubic phase compensation and obtained pulses of 6fs full width half maximum (FWHM). However, the tunability of this special dye laser configuration is extremely restricted and limits the application to spectroscopic investigations rather severely. Therefore, sometimes old-fashioned and less sophisticated techniques such as the simple synchronous pumping of a dye... 

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