User`s manual

7
Femtosecond Pulse Compressor
The pulse compressor was designed for compression of
picosecond pulses amplified by Wedge 50 multipass Ti: sapphire
amplifier to pulses as short as 50-100 fs. The principle of pulse
compressor operation is shown in the Figure 3. One can see that
in contrast to the pulse stretcher, redder frequency components
have to travel further through the compressor than the bluer
frequency components. The result is that the pulse has been
compressed. Varying distance between the gratings, the
compression can compensate the stretching precisely giving
almost the same pulse duration as obtained from the seed laser
pulse. The Figure 3 shows a simplified pulse compressor. In the
Wedge 50 pulse compressor some other optics are involved, i.e.
horizontal and vertical retroreflectors give a possibility to use
one grating and to achieve four-pass configuration. High
reflective gold coated holographic grating gives stretcher
efficiency higher than 50% for specific wavelength regimes.
Femtosecond Confocal Multipass Ti:sapphire Amplifier
The confocal multipass amplifier has been designed as an
effective device for amplification of femtosecond pulses in
different active media. Our unique design features two
confocally placed concave mirrors of different radii of curvature
(ROC) with central holes (Figure 4). This telescopic
configuration provides six, eight, ten passes of the light beam
through the common focus where Ti : sapphire crystal is
placed. Due to different focal lengths of the mirrors, beam cross
section is decreased after each pass and the beam waist diameter
is increased accordingly. On the sixth pass the beam waist
diameter is about four times more than on the first one. This is
an important condition for getting the maximum gain, and one
cannot find this feature in other multipass or regenerative
amplifier systems. The pump radiation is focused by the lens
through an aperture in the input mirror.