An optical trap for storing femtosecond laser pulses for enhanced interaction efficiency with optically thin targets was investigated theoretically. The optical trap (Fig.1.) consists of an electro-optical switch, four high reflecting mirrors, and a focusing system. The efficiency of the optical trap strongly depends on the optical losses . To compensate the optical losses we intend to use Ti:Sapphire as an amplifying medium which has high saturation fluence ≈ 0.9 Jcm−2, and upper state lifetime of 3.2 μs. These parameters of the amplifying medium do not cause a quick extraction of the stored energy  and will keep the laser pulse intensity constant over 3.2 μs. In the theoretical investigations, we had studied the trapping of femtosecond laser pulse of wavelength 800 nm, 1mJ energy per pulse, 10 Hz repetition rate and with different times of 100 fs, 200 fs, 500 fs, 700 fs, 1 ps and 2 ps. Due to propagation of these laser pulses through the optical elements that form the optical trap both of phase self modulation and group velocity dispersion, introduce an additional broadening for laser pulses that have the initial duration time <700 fs. To compensate this broadening, chirped mirror with suitable properties can be used. Power consideration showed an increase in the average power of the optical trap which includes a Ti: Sapphire by a factor of 100 times compared to single passage of the laser pulse. Also the laser pulse could be stored in the optical trap for 5.5 μs. This will be great benefit in applications that used high power pulsed laser systems including possible medical applications.
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