All-solid-state femtosecond diode-pumped Cr:LiSAF laser - Electronics ...

43 downloads 0 Views 228KB Size Report
Indexing terms: Lasers, Optical pumping. A femtosecond diode-pumped Cr:LiSAF laser has heen demonstrated for the first time. A multiquantum well absorber.
4

KASHYAP, R., ARMITAGE, J.R., WYSTT, R., DAVEY, s.T., and WILLIAMS, o.L.: ‘All-fibre narrowband reflection gratings at

5

LEGOUBIN, S., FERTEIN, E., BAYON, F., and FEORFES, T.:

1500nm’, Electron. Lett., 1990, 26, (II), pp. 730-732 OOUAY, M.,

BERNAGE, P.,

NIAY, P.,

‘Formation of Moire grating in core of germanosilicate fibre by transverse holographic double exposure method’, Electron. Lett., 1991, 27, (21), pp. 1945-1947

6

BEYLAT, J.L., HEBERT, J.P., BRILLOUET, F., PROVOST, J.P., BODERE, A., PAFNOD-ROSSIAUX, P., MATABON,M., C R E T ~Y., , and HAJJ, M.: ‘Very

mismatches of less than a few millimetres, we observe bunches of femtosecond pulses separated by the cavity mismatch. Fig. 1 shows the autocorrelation trace and spectrum of such pulse train bunches. For zero mismatch between the cavities, the laser output becomes extremely unstable and no pulse trains are observed. We have not been able to eliminate the multiple pulse operation and conclude RPM is not the best approach for generating stable single femtosecond pulse trains.

reproducible 1.55pm DFB laser source with simultaneous low chirp and high linearity for CATV distribution systems’. ECOC ’92, 1992, (Berlin), Paper Th PD 11-2, pp. 895-897

All-solid-state femtosecond diode-pumped Cr:LiSAF laser MQ W absorber

P.M. Mellish, P.M.W. French, J.R. Taylor, P.J. Delfyett and L.T. Florez

/I

Indexing terms: Lasers, Optical pumping A femtosecond diode-pumped Cr:LiSAF laser has heen demonstrated for the first time. A multiquantum well absorber has heen used in a dispersion-compensated cavity to yield CW trains of transform-limited femtosecond pulses.

Titanium-doped sapphire (Ti:AI,O,) lasers can routinely generate tunable femtosecond pulses in the near infra red [I] and recently, pulse durations below 20 fs have been achieved, e.g. see [2]. Unfortunately, the requirement for an argon ion pump laser makes it impractical for some applications. Cr”:LiSrAIF,(Cr:LiSAF) provides a vibronic laser medium with a comparable emission band and absorption bands suitable for diode pumping at 670nm [3]. Modelocking of this laser medium has been demonstrated using Kerr lens modelocking (KLM) with a variety of schemes to initiate the pulse formation. An acousto-optic modulator was employed to yield pulses as short as 50fs [4] and a saturable absorber dye to obtain pulses as short as 33fs in a laser cavity with low dispersion F2 prisms [5]. Subsequently a solid-state laser laser oscillator with an intracavity MQW absorber yielded transform-limited pulses as short as 93fs for less than 5OOmW absorbed pump power at 488nm [6]. This pump power is compatible with the output powers of commercially available 670nm laser diodes and suggests that an all-solid-state femtosecond Cr:LiSAF laser should be possible. Pulse formation in this particular laser was thought to begin with passive modelocking by the resonant MQW saturable absorber and evolve to a KLM steady state. Diode pumping of Cr:LiSAF is aided by a reasonably long ( - 6 7 ~ )upper-state lifetime and has been demonstrated for CW lasers at -670nm [7,8] and in the wing of the absorption profile around 760nm [9]. We previously reported [lo] the first modelocking of diode-pumped Cr:LiSAF lasers. Initially a CW laser was demonstrated which delivered up to -30mW of true CW output power with a 1% output coupler. The laser threshold was 70mW pump power with no output coupler and the laser tuned from 799 to 860nm, this tuning range being limited by the dielectric mirror coatings. Active modelocking was demonstrated using an acoustooptic modulator at a resonance frequency of -40.4MHz. The pulses were of -3OOps duration and the laser operated very close to threshold. Resonant passive modelocking (RPM) [I I] was then employed to demonstrate an all-solid-state passively modelocked laser, using the MQW absorber of [6] in an external cavity. Stable CW modelocked pulse trains at 250MHz were observed which were measured to be