Phase-modulated femtosecond laser pulses

Figure 6.3 Shaped femtosecond laser pulses from sinusoidal spectral phase modulation of an 800 nm, 20 fs FWHM input pulse. The left column shows the modulated pulses in the frequency domain, decomposed into spectral amplitude (gray line and background) and modulation...

V. Coherent Control with Phase-Modulated Femtosecond Laser Pulses... 

V. COHERENT CONTROL WITH PHASE-MODULATED FEMTOSECOND LASER PULSES... 

Active control of population transfer using the control relation displayed in Eq. (5.23) has been demonstrated experimentally by Sherer et al. [18]. In this experiment gaseous I2 was irradiated with two short (femtosecond) laser pulses the first pulse transfers population from the ground-state potential-energy surface to the excited-state potential-energy surface, thereby creating an instantaneous transition dipole moment. The instantaneous transition dipole moment is modulated by the molecular vibration on the excited-state surface. At the proper instant, when the instantaneous transition dipole moment expectation value is maximized, a second pulse is applied. The direction of population transfer is then controlled by changing the phase of the second pulse relative to that of the first pulse. 

Valdmanis J A and Fork R L 1986 Design considerations for a femtosecond pulse laser balancing self phase modulation, group velocity dispersion, saturable absorption, and saturable gain IEEE J. Quantum. Electron. 22 112-18... 

The study confirmed that the action of the precursors of the main pulse has to be carefully considered in the ultrashort intense laser pulse interactions. Nevertheless, a regime of rather stable propagation [34] of a laser pulse of tens of femtoseconds was found in a broad window of the laser intensity/medium density diagram, in which (1) the ionization occurs in one or a few optical cycles, avoiding effects of self-phase modulation and defocusing for most of the... 

The spectral width of a pulse train emitted by a femtosecond laser can be significantly broadened in a single mode fiber [27]. This process that maintains the mode structure is described in the time domain by the optical Kerr effect or selfphase modulation. The first discussion is simplified by assuming an unchanging pulse-shape under propagation. After propagating the length l the intensity dependent refractive index n(t) = n0 + ri2/(f) leads to a self induced phase shift... 

FIGURE 16 Additive pulse mode-locked laser. The output of the color center laser is coupled to an optical fiber. Self-phase modulation in the fiber adds bandwidth to the pulse, which is coupled back to the laser. The combination produces femtosecond-duration pulses. (OC, output coupler BS, beam splitter BTP, birefringent tuner plate HR, high reflector PZT, piezotransducer). 

The frequency spectrum of a mode-locked continuous laser emitting a regular train of short pulses consists of a comb of equally spaced frequency components (the modes of the laser resonator). The spectral width of this comb spectrum depends on the temporal width of the laser pulses (Fourier theorem). With femtosecond pulses the comb spectrum extends over more than 30 THz. The spectral width can be further increased by focusing the laser pulses into an optical fiber, where by self-phase modulation the spectrum is considerably broadened and extends over one decade (e.g., from 1064nm to 532nm). This corresponds to a frequency span of 300THz [14.157] ... 

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