A self mode-locked titanium sapphire laser has been constructed following the design of Murnane, Kapteyn, Huang, Asaki and Garvey from Washington State University. This laser produces the shortest pulses available directly from a laser oscillator. It is based in a very simple design which comprises two end mirrors, one of which is an output coupler, two fold mirrors which focus the beam into the Ti:Sapphire crystal and a pair of prisms which compensate the temporal dispersion associated with the crystal. The laser is pumped with approximately 5W of multi-line output from a continuous wave argon ion laser. Short pulses are achieved by minimizing the third order phase dispersion in the laser cavity. This involves the use of a small, 4.75 mm crystal, single stack cavity mirrors which are chosen to give the flattest spectral response over about 150 nm and a pair of fused silica prisms instead of the more commonly used dispersive glasses. Typical pulse widths from the laser are between 11 and 13 fs at a repetition rate of 85 MHz with a power of about 5 nJ. The noise is only that arising from the argon pump laser, typically less than 1%. The high repetition frequency and reasonable high peak power will allow some measurements to be done directly using lock-in detection. However, for most applications the laser will need to be further amplified. This was achieved in a new design of regenerative amplifier but a small loss in temporal resolution will result. It is believed that a high energy pulse around 1 mJ can be produced at a 1 kHz frequency having a width between 30 and 50 fs. The generation of a white light continuum from this source will allow pump probe experiments to be performed throughout the visible region of the spectrum. Frequency doubling and difference frequency generation will alsoyield high powered near UV and infra-red pulses with sub 100 fs pulse widths (see progress report for recent accomplishments using improved designs).
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