Dynamic Pulse Shaping
Dynamic Pulse Shaping
Tuesday, 7 September 2004
Pulses from ultrafast lasers can be shaped in time by modifying the relative phase between their constituent wavelength components. Various experiments exist that require shaped femtosecond optical pulses. For example, in femto-chemistry highly structured chirped pulses can be required to excite particular molecular bonds.
Our research concentrates on shaping 800nm pulses from a femtosecond Ti:sapphire laser using an adaptive-optic pulse shaper (see below) with a deformable mirror (DM) situated at the Fourier plane of the lens (FL). Pulses from the laser are coupled into the shaper and dispersed by a diffraction grating (DG) to form a line spectrum. The spectral phase of the pulses is modified by programming a chosen curvature onto the mirror surface. Examples of pulse shapes (red curves) that are in principle realisable using particular mirror deformations (black curves) are illustrated below.
The screenshot (right) shows the system after running for around 30 seconds. The FROG trace of the pulses is shown in the top-left window and their retrieved phase is the red line in the spectral phase window (top-right). The target spectral phase is the blue line in the same window and shows the close agreement achieved.
Quicktime movies showing the pulse shaper in action for different target shapes can be downloaded from the list below. The typical download size is < 1 Mb.
Compression of an initially chirped pulse;
Creation of approximately linearly chirped pulses with small and large chirp;
Creation of pulses with small and large nonlinear chirps;
Creation of an asymmetric pulse.
To view these movies you will need Apple Quicktime Player.
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