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Femtosecond chain

par Nunzia SAVOIA - publié le , mis à jour le

Ti:Sapphire chain of the laboratory is based on the Chirped Pulse Amplification (CPA) technique introduced in 1985 by D. Strickland et G. Mourou


The concept behind CPA is a scheme to increase the energy of a short pulse, while avoiding very high peak powers in the laser amplification process itself. This is done by lengthening the duration of the pulse being amplified, by dispersing, or ‘‘chirping’’, it. By lengthening the pulse in time, energy can be efficiently extracted from the laser gain medium and avoiding damage to the optical amplifier. CPA is particularly useful for efficient utilization of solid-state laser media with high stored energy density (1 – 10 J/cm2), where full energy extraction in a short pulse would lead to intensities above the damage threshold of the amplifier materials. The CPA scheme works as follows (see Figure) : ultrashort light pulses are generated at low pulse energy through the use of an ultrashort-pulse modelocked laser oscillator. This modelocked laser typically generates light pulses at a high repetition rate ( 100 MHz) with pulse energies in the range of 10-9 J and with pulse durations in the range of 10-12–10-14 s. These pulses are then chirped using a dispersive delay line consisting of a diffraction-grating arrangement. The pulse is stretched from a duration under 100 fs to typically 100 ps, decreasing its peak power by three orders of magnitude. One or more stages of laser amplification are used to increase the energy of the pulse, by six to nine orders of magnitude, to a fluence sufficient to efficiently extract energy from the laser amplifier. After optical amplification, when the pulse is very energetic, a second grating pair is then used to recompress the pulse back to initial duration.
Femtosecond chain components

- Femtosecond oscillator Ti:Sapphire, Spectra Physics model TSUNAMI
76 MHz, 40 fs, 4 nJ
- Regeneratif amplifier, Spectra Physics model SPITFIRE
Repetition rate : 1 KHz-4 Hz
Pulse energy : 2 mJ

Regime 1 Regime 2 Regime 3
40 fs 120 fs 1-2 ps
Bandwidth 34 nm 10 nm 1 nm
Peak Power 50 GW 17 GW 2-1 GW

- Femtosecond Optical Parametric Amplifier, Light Conversion model TOPAS-C, wavelength tuning between 240 nm-20 µm
- Picosecond Optical Parametric Amplifier Light Conversion model TOPAS-800-ps, wavelength tuning between 240 nm-20 µm

Nunzia Savoia
Research Engineer
phone : +003 20 33 64 62 (office)
phone : +003 20 43 41 65 (lab)

Marc Le Parquier
Optical and Instrumentation Engineer
phone : +003 20 33 64 72 (office)

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