Robert Bedford

Tunable high-power high-brightness linearly polarized vertical-external-cavity surface-emitting lasers

We report on the development and the demonstration of tunable high-power high-brightness linearly polarized vertical-external-cavity surface-emitting lasers (VECSELs). A V-shaped cavity, in which the antireflection-coated VECSEL chip (active mirror) is located at the fold, and a birefringent filter are employed to achieve a large wavelength tuning range. Multiwatt cw linearly polarized TEM00 output with a 20nm tuning range and narrow linewidth is demonstrated at room temperature.

5-W Yellow Laser by Intracavity Frequency Doubling of High-Power Vertical-External-Cavity Surface-Emitting Laser

We report on the development of a high-power tunable yellow-orange laser. It is based on intracavity frequency doubling of a widely tunable, highly strained InGaAs-GaAs vertical-external-cavity surface-emitting laser operating near 1175 nm. Over 5 W of continuous-wave output power is achieved and is tunable over a 15-nm band centered at 587 nm. This compact low-cost high-power yellow-orange laser provides an innovative alternative for sodium guidestar lasers, medical and communication applications.

High temperature stability of postgrowth annealed transparent and conductive ZnO:Al films

High temperature stability of Al-doped ZnO transparent thin films in air has been improved by a combination of optimized growth parameters and postgrowth treatment. Optical transparency was better than 90% for wavelengths ranging from 380 to at least 2500nm with films that also had resistivities of 2×10−4Ωcm. Depending on the growth conditions, film resistivities showed different degrees of increase in resistivity after storing in air at elevated temperatures. Films grown at lower pressures were stable up to 400°C for short exposure times (2h) and exhibited virtually no change in resistivity at 260°C for over 2500h.

Highly strained InGaAs∕GaAs multiwatt vertical-external-cavity surface-emitting laser emitting around 1170nm

We develop and demonstrate a multiwatt highly strained InGaAs∕GaAs vertical-external-cavity surface-emitting laser with a free lasing wavelength of around 1170nm. This laser can be tuned from ∼1147to∼1197nm. This low-cost compact wavelength agile laser can potentially provide high-power coherent light in a wide yellow-orange band by the intracavity frequency doubling.

Tunable watt-level blue-green vertical-external-cavity surface-emitting lasers by intracavity frequency doubling

We report on the development and the demonstration of a tunable, watt-level, blue-green, linearly polarized vertical-external-cavity surface-emitting lasers operating around 488nm by intracavity second-harmonic generation. By using lithium triborate crystal, we have achieved over 1.3W continuous wave blue-green power at 488nm with a 5nm tunability.

Linearly polarized dual-wavelength vertical-external-cavity surface-emitting laser

Abstract : The authors demonstrate the multiwatt linearly polarized dual-wavelength operation in an optically pumped vertical-external-cavity surface-emitting laser by means of an intracavity tilted Fabry-Perot etalon and a Brewster window. The sum frequency generation from the lithium triborate crystal pumped by this laser confirms that these two wavelengths oscillate simultaneously. Over 30 dB side-mode suppression can be achieved at dual wavelengths with a spectral spacing of 2.1 nm. The output power is slightly reduced by the intracavity Fabry-Perot etalon and Brewster window.

Multichip vertical-external-cavity surface-emitting lasers: a coherent power scaling scheme

We propose an efficient coherent power scaling scheme, the multichip vertical-external-cavity surface-emitting laser (VECSEL), in which the waste heat generated in the active region is distributed on multi-VECSEL chips such that the pump level at the thermal rollover is significantly increased. The advantages of this laser are discussed, and the development and demonstration of a two-chip VECSEL operating around 970 nm with over 19 W of output power is presented.

Extended Tunability in a Two-Chip VECSEL

We demonstrate a widely tunable vertical-external-cavity surface-emitting laser (VECSEL) with a W-shaped cavity, in which two VECSEL chips serve as fold mirrors and a birefringent filter is inserted at Brewsters angle. These two chips provide much higher modal gain and broader bandwidth of the gain than a single chip does, enhancing the VECSEL tuning range and reducing the variation of tunable output power with the tuned wavelength. This two-chip VECSEL configuration makes it possible to shape the modal gain spectra of the laser or to manipulate the tuning curve of the laser by two different chips with certain gain peak detuning (offset). Multiwatts high-brightness linearly polarized output with a tuning range of 33 nm is demonstrated in such a two-chip VECSEL

Broadband saturable absorption and optical limiting in graphene-polymer composites

Nonlinear optical properties of a graphene-polyvinyl alcohol composite are studied using an irradiance-scan setup. The measurements are carried out at 785 nm and 1064 nm in the nanosecond and picoseconds temporal regimes, respectively. It is shown that the output fluence readily clamps with increasing input and graphene concentration due to nonlinear absorption and scattering. Furthermore, the nonlinear transmission demonstrates weak saturable absorption followed by strong optical limiting. The nonlinear coefficients βeff and Isat calculated via numerical fitting show that βeff depends on the graphene content and increases significantly in nanosecond regime due to high degree of thermally induced nonlinear scattering.

Power-limiting mechanisms in VECSELs

Vertical external cavity surface emitting lasers (VECSELs) have been considered the “ultimate disk-laser” due to their extremely thin active regions and because they take advantage of the high gain found in semiconductor material. This paper discusses power scaling limitations, including heating effects, surface roughness losses, and laterally guided amplified spontaneous emission (ASE).