Abstract

Stimulated Raman scattering (SRS) is a powerful tool for generating a frequency shifted coherent field. SRS is usually achieved by introducing an intense laser field into a Raman cell or by using an intracavity Raman cell inserted in a laser resonator. On the other hand, laser-diode (LD) pumped microchip lasers have a wide variety of applications where the Nd-doped lasers are mostly used for practical devices, including new wavelength generation. In such lasers, a circulating intensity of an intracavity laser field is thought to be high due to the microcavity configuration, while activation of phonon energies by impurity ions can be expected in laser materials. Recently, we demonstrated intracvity phonon-assisted emissions in LD-pumped microchip Nd:YAG, Nd:YVO₄ (yttrium orthovanadate), and LiNdP₄O₁₂ (LNP), lasers without using any Raman cell. Stokes shifts are about 3000 cm^–1, yielding Stokes emissions around 1.5 µm. Such a phonon-assisted frequency conversion is unique and the development of microchip Raman lasers is attractive. Here, we report more on phonon-assisted frequency conversion in such Nd:doped lasers by using an IR tunable laser. In experiments, a 1.0% doped Nd:YAG with 5mm thickness, a Nd:YVO4 with 0.5 mm thickness (3% atm doped) and 1mm thickness (1% atm doped) were used. Both sides of the laser crystals were coated to be highly-reflective at the lasing wavelength of 1064 nm. The transmission at 1560 nm was about 55% for all cases. In experiments, the laser crystals were temperature-controlled. Our pumping source was a LD oscillating at 810 nm where additional input port was designed to include the IR beam from the tunable laser source (HP81682A; wavelength resolution: ±0.1 pm). A multiwavelength meter (HP-86120B) and a monochromator (ARC, Spectra Pro-500), in which the IR emission was enhanced (with FJW 84499A-5) and recorded by a CCD, were used to monitor the wavelength variations. The frequency conversions raised by the wave-mixing processes, which were further induced by the emission from tunable laser, as well as the depletion and the enhancement of IR emissions were investigated. Numerical exploration based on model equations was provided.

© 2001 EPS