Pump Overlap Research Articles

Investigation of structural dependence of host erbium-doped triangular-lattice PCF on lasing properties and design of high performance laser

A detailed study is presented on the lasing properties of an erbium-doped photonic crystal fiber (PCF) laser. The effects of the host PCF’s structure and laser parameters on continuous-wave laser emission are analyzed by considering the confinement and overlap of pump and signal fields in the gain medium for varying values of pitch, hole diameter, and doping radius. For analysis, we used a finite-difference mode-calculation algorithm devised with standard population and propagation rate-equation solver. Our analysis, applied to an experimentally realized PCF laser, reproduces the observed/reported data, thereby showing the efficacy of our analysis. Finally, a fiber geometry to realize a laser with threshold as low as 6 mW using a short fiber length of 0.52 m is prescribed. The aim of the design is to greatly reduce splice loss with standard single-mode SM28/G.652 fiber while maintaining the optimum performance. These results are new in PCF laser research and should be useful in realizing high performance PCF-based laser devices.

Theory of attosecond transient-absorption spectroscopy of krypton for overlapping pump and probe pulses

We present the first fully ab initio calculations for attosecond transient absorption spectroscopy of atomic krypton with overlapping pump and probe pulses. Within the time-dependent configuration interaction singles (TDCIS) approach, we describe the pump step (strong-field ionization using a near-infrared pulse) as well as the probe step (resonant electron excitation using an extreme- ultraviolet pulse) from first principles. We extent our TDCIS model and account for the spin-orbit splitting of the occupied orbitals. We discuss the spectral features seen in a recent attosecond transient absorption experiment [A. Wirth et al., Science 334, 195 (2011)]. Our results support the concept that the transient absorption signal can be directly related to the instantaneous hole population even during the ionizing pump pulse. Furthermore, we find strong deformations in the absorption lines when the overlap of pump and probe pulses is maximum. These deformations can be described by relative phase shifts in the oscillating ionic dipole. We discuss possible mechanisms contributing to these phase shifts. Our finding suggests that the non-perturbative laser dressing of the entire N -electron wave function is the main contributor.

Ion-exchanged silica-on-silicon structured channel erbium-doped waveguide amplifiers

Silica-on-silicon structured channel erbium-doped waveguide amplifiers (EDWAs) were fabricated by a combination of the ion-exchange and sol-gel techniques. A small signal fiber-device-fiber net gain of 0.5 dB at 1531 nm was obtained for a 4 cm long EDWA with an optimized waveguide structure. The low noise figure of 4.0 dB was also achieved. Samples of different waveguide structures and rare-earth ion doping levels were fabricated to compare the EDWA gain properties. The results demonstrate that a better gain spectrum can be obtained by maximizing the distribution overlap of pump and signal mode intensity. The gain performance can be further improved by reducing upconversion efficiency of the EDWA. This work demonstrates that the ion-exchanged silica-on-silicon waveguide structure is an alternative approach for EDWA fabrication.

Analysis of confinement effects on microstructured Ln^3+:KY_1-x-yGd_xLu_y(WO_4)_2 waveguides

High quality KY1-x-yGdxLuy(WO4)2 lattice matched layers activated with Er3+ and Tm3+ have been grown by liquid phase epitaxy on KY(WO4)2 substrates. From these active layers, we have fabricated channel waveguides by dry etching of their surface through Ar ion milling. The effects on the confinement and overlap of pump and laser modes and on the optical losses of the waveguides due to a cladding layer with the same composition of the substrate grown on these microstructured waveguides have been analyzed. The results clearly show the beneficial effects that this strategy presents, such as a better confinement, a better overlap and specially reduced optical losses when compared to the surface channel waveguides.

A three-level analytic model for alkali metal vapor lasers: part I. Narrowband optical pumping

A three-level analytic model for optically pumped alkali metal vapor lasers is developed by considering the steady-state rate equations for the longitudinally averaged number densities of the ground 2S1/2 and first excited 2P3/2, and 2P1/2 states. The threshold pump intensity includes both the requirements to fully bleach the pump transition and exceed optical losses, typically about 200 W/cm2. Slope efficiency depends critically on the fraction of incident photons absorbed and the overlap of pump and resonator modes, approaching the quantum efficiency of 0.95–0.98, depending on the alkali atom. For marginal cavity transmission losses, peak performance is achieved for low output coupling mirror reflectivity. For efficient operation, the collisional relaxation between the two upper levels should be fast to prevent bottlenecking. By assuming a statistical distribution between the upper two levels, the limiting analytic solution for the quasi two-level system is achieved. For properly designed gain conditions, the quasi two-level solution is usually achievable and represents ideal performance.