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Femtosecondlight pulses tunable between 840 nm and 880 nm are generated in a synchronously pumped ring dye laser. The laser emits nearly bandwidth-limited pulses ( Av t,, = 0.45) with pulse durations down to 65 fs. At a pumping power of 450 mW of a mode-locked Ar-ion laser (X = 514 nm) the infrared femtosecond dye laser has an output of up to 15 mW.The generation of light pulses around 100 fs was made possible by the introduction of the colliding pulse mode-locking technique [ 11. The specially designed laser produced femtosecond light pulses in the spectral range around 620 nm. The advanced understanding of the pulse shaping process and the introduction of an intracavity compensation of dispersion allowed the stable generation pulses between 27 fs and 100 fs [2-51. While the standard CPM laser operates with cw pumping by an argon ion laser, attempts have been made to synchronously pump CPM lasers. Recently we were able to show that -by using a specially designed pumping scheme -stable CPM laser action is possible with synchronous pumping [6]. This laser system was further advanced now generating 60 fs pulses at 625 nm [7]. The major draw-back of CPM dye lasers is the very narrow wavelength range. Up to now the emission of femtosecond lasers is restricted to wavelengths between 600 nm and 635 nm. Femtosecond light pulses at other wavelengths have been produced with complex and expensive systems after amplification of the red femtosecond pulses and subsequent continuum generation [8,9].In this letter we report on the first operation of a femtosecond laser in a new wavelength range. The wavelength of the femtosecond pulses is located in the near infrared; the tunability extends from 840 to 880 nm. Stable pulse trains with pulse durations as short as 65 fs were achieved.The construction of the infrared femtosecond laser 0 0304018/86/$03.50 0 Elsevier Science Publishers B.V. (North-Holland Physics Publishing Division) is similar to a standard CPM laser [I ,3]. The laser resonator consists of a ring cavity formed by dielectrically coated mirrors (peak reflectivity around 850 nm). The amplifying jet (dye Styry19, 1 g/Q dissolved in a mixture of propylene carbonate and ethylene glycol, 1 : 4, pumped through a nozzle of thickness 0.3 mm) is in the focal region of a pair of curved mirrors (R = 100 mm). The absorber jet (dye IR 140, dissolved in benzylalcohol, c = 0.1 g/Q for a thickness of the nozzle of 0.3 mm) is in the focus of a second pair of mirrors (R = 50 mm). The dispersion of the laser cavity could be adjusted by four brewster prisms [3]. The output mirror (R = 90%) is mounted on a highprecision translation stage. The cavity length of the dye laser is adjusted carefully in order to match the round-trip time of the dye laser to that of the pumping laser. The pumping Ar-ion laser is operated at a repetition rate of 73.3 MHz and at a pumping power of 450 mW at X = 5 14 nm. The final alignment of the dye laser requires a careful adjustment of both the cavity length (within 100 nm) and the dispersion of the prism sys...