A Pr³⁺-doped single-mode fibre laser

The rare-earth doped single-mode fibre laser has emerged as a new source of laser radiation in the near infrared region of the spectrum. Using an Ar+-ion, dye or semiconductor laser as a pump source, low threshold CW or pulsed operation is possible over a wide range of wavelengths. Low threshold CW laser emission is also possible on 3-level transitions at room temperature with no auxiliary cooling requirements. As an example, laser operation has been obtained at 1085nm on the 1G4 - 3H4 (groundstate) transition of Pr3+-ions in glass. The excitation source was a CW Rh6G dye laser operating at 590nm, although such was the absorption of the Pr3+-doped fibre that most of the Rh6G emission spectrum could be used for pumping. Using a cleaved fibre butted to two dielectric mirrors having high reflectivity at the lasing wavelength, CW threshold was found to occur for 10mW of absorbed power at 590m. Q-switching has been obtained using an intracavity acousto-optic modulator. In preliminary experiments using a non-optimised cavity, we have obtained pulses of 500ns duration and >1W peak power at a repetition rate of several kHz. Using a more efficient configuration, over an order of magnitude increase in peak power is anticipated. By replacing the output mirror with a diffraction grating blazed at 1µm, a 61m tuning range from 1048nm - 1109nm has been obtained. Using an alternative pump source, visible operation of this laser may be possible