| Summary: | A multiatmospheric-pressure-broadened CO₂ laser amplifier was constructed
to amplify sub-10-picosecond pulses generated with semiconductor switching.
High-intensity, mid-infrared, amplified pulses have many applications:
especially in fields such as non-linear optics, laser-plasma interaction, and
laser particle acceleration. The injected pulses are produced by exciting GaAs
(or an engineered, fast-recombination time semiconductor) with an ultrafast
visible laser pulse to induce transient free carriers with sufficient density to
reflect a co-incident hybrid- CO₂ laser pulse. The short pulse is injected
directly into the regenerative amplifier cavity from an intra-cavity semiconductor
switch. The CO₂-gas-mix amplifier is operated at 1.24 MPa which is
sufficient to collisionally broaden the individual rotational spectral lines so
that they merge to produce a gain spectrum wide enough to support pulses
less than 10 ps long. After sufficient amplification, the pulse is switched out
with another semiconductor switch pumped with a synchronized visible-laser
pulse. This system is demonstrated and analysed spectrally and temporally.
The pulse-train spectral analysis is done for a GaAs-GaAs double-switch
arrangement using a standard spectrometer and two HgCdTe detectors; one
of which is used for a reference signal. An infrared autocorrelator was designed
and constructed to temporally analyse the pulse trains emerging from
the amplifier. Interpretation of the results was aided by the development of
a computer model for short-pulse amplification which incorporated saturation
effects, rotational- and vibrational-mode energy redistribution between
pulse round trips, and the gain enhancement due to one sequence band. The
results show that a sub-10-picosecond pulse is injected into the cavity and
that it is amplified with some trailing pulses at 18 ps intervals generated by
coherent effects. The energy level reached, estimated through modelling, was
>100 mJ/cm². === Science, Faculty of === Physics and Astronomy, Department of === Graduate
|
|---|
