Pump-probe spectroscopy of molecular systems requires high average power, short pulse, mid-infrared sources. Today OPO deliver wavelengths up to 4 µm and THz systems supply wavelengths beyond 20 µm. To achieve tunable wavelengths in between these two regions, the signal and idler beams of the OPO can be difference frequency mixed again. This two-step nonlinear process necessarily leads to average power much less than the OPO pump, which is typically a 1 W Ti:sapphire laser. In this paper, we report initial experimental results of two-wavelength amplification in a Yb-doped DCF fiber. Yb:fibre amplifiers have been shown to deliver short pulses at average power levels of up to 20 W[1] .The goal of the work is to generate high average power (<1W) pump and signal beams for difference frequency generation at around 15 µm.
A schematic of the experimental is shown in Fig.1. A photonics crystal fiber is pumped by a mode-locked Ti:Sapphire laser to create supercontinuum, from which we can select the two seed wavelengths by using a standard zero dispersion grating line that has been adapted to have individual mirrors in the focal plane for the two different colours. The Yb:fibre is pumped by a 915nm diode laser. As shown in Fig. 2, at a pump power of 2.1 W, 500 gain was achieved yielding 150 mW total power(1055 and 1095 nm).
References:1. D. Nickel et al, Opt. Commun. 190, 309 (2001)
Brillouin scattering spectra in a photonic crystal fiber with partially Ge-doped core is demonstrated, for the first time to our knowledge, using pump-probe technique. We have observed and characterized Brillouin spectra in the photonic crystal fiber at 1320 nm. One main peak and several sub-peaks are observed. Brillouin loss spectrum of main peak has a Lorentzian shape. The bandwidth ΔνB is 66 MHz and the Brillouin frequency shift νB is 12.054 GHz at room temperature. The peak originating from a higher order guided longitudinal acoustic mode in the graded-Ge-doped core of the photonic crystal fiber is observed for the first time. The temperature related behavior of the photonic crystal fiber is investigated. It is shown a linear dependence for the photonic crystal fiber.
PMD characteristics of four commercial photonic crystal fibers are measured using Jones Matrix eigenanalysis. It is found that PMD value could vary up to two orders of magnitude due the asymmetry of the photonic cyrstal fiber fabrication. The PMD temperature dependent characteristics is presented for a 1.55μm crystal fiber.
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