Ho:YAG is an attractive laser material for high power operati on in the eyesafe 2μm wavelength regime due a combination of good thermo -mechanical properties and favourable spectroscopic properties. A particularly attractive feature is the long fluorescence lifetime (~8ms), which allows the production of high Q -switched pulse energies. Unfortunately, direct pumping of Ho:YAG by near -infrared diodes lasers requires that the crystal is co-doped with Tm, leading to high upconversion losses and reduced efficiency, particularly when operating in the Q-switched regime. One solution to this problem is to use singly-doped Ho:YAG crystals and pump directly into the upper laser level manifold with a diode -pumped Tm:YLF  or Tm:YVO4 laser. This approach has the advantages that upconversion losses are much lower and quantum defect heating in th e Ho:YAG is greatly reduced, leading to very high lasing efficiencies. The upper limit on output power is, however, limited by thermal effects in the Tm -doped crystal laser. An alternative approach is to use a cladding -pumped Tm-doped fiber laser as the pump laser. Cladding -pumped fiber lasers are relatively immune from thermal effects and hence offer the potential for scaling to very high powers without degradation in beam quality. In addition, the broad emission linewidth allows the lasing wavelength to be tuned over a very wide range. The combination of high power, high brightness and flexibility in operating wavelength suggests that cladding-pumped Tm-doped fibers lasers would be ideal pump sources for many Tm and Ho doped crystal lasers. In recent work, we reported a tunable cladding -pumped Tm-doped silica fiber laser with lasing wavelength tunable from 1860nm-2090nm at multi-watt power levels . In this paper we describe recent results for a tunable cladding-pumped Tm-doped silica fiber laser with improved performance and preliminary results for Ho:YAG laser pumped by the Tm fiber laser.
© 2003 Optical Society of AmericaPDF Article