Laser providing stable femtosecond pulses

DETAILED DESCRIPTION To this end the present invention provides, in combination: an auxiliary mode-locked synchronous pumping laser; a main laser cavity, including a dye amplifier assembly pumped by the auxiliary laser together with a saturable absorbent assembly; and stabilization means suitable for adjusting the optical length of the main laser cavity as a function of the difference between the spectrum of the pulses produced thereby and a desired central wavelength, and in a direction suitable for reducing said difference.
More particularly, the stabilization means comprise: means for tapping a small portion of the laser beam produced; means for comparing the spectral position of said small portion relative to the desired central wavelength; and means for adjusting the optical length of the main laser cavity as a function of said comparison and in a direction tending to latch the spectrum onto the desired central wavelength.
Preferably, the outlet mirror of the main cavity is mounted on a piezo-electric stack controlled by the stabilization means in order to adjust said optical length.
Most advantageously, the main laser cavity is at least partially disposed in a ring containing the saturable absorbent assembly, such that two pulses running round the ring in opposite directions collide with each other within the saturable absorbent (CPM operation).
In one embodiment of the invention, the main laser cavity includes a first optical path on one side of the dye amplifier assembly and passing via a separator blade disposed to transmit the laser beam to two facing mirrors in a symmetrical disposition about the saturable absorbent assembly.
Preferably, the main laser cavity also includes a prism assembly suitable for adjusting the group dispersion of the laser beam inside the cavity.
Yet more particularly, the stabilization means make use of beam leakage through one of the two facing mirrors and acts on the position of the outlet mirror.
Any other method of tapping the laser beam could also be used