Chris Hessenius

Continuous-wave all-solid-state 244 nm deep-ultraviolet laser source by fourth-harmonic generation of an optically pumped semiconductor laser using CsLiB6O10 in an external resonator

We report an all-solid-state laser system that generates over 200 mW cw at 244 nm. An optically pumped semiconductor laser is internally frequency doubled to 488 nm. The 488 nm output is coupled to an external resonator, where it is converted to 244 nm using a CsLiB(6)O(10) (CLBO) crystal. The output power is limited by the available power at 488 nm, and no noticeable degradation in output power was observed over a period of several hours.

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.

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.

High-power tunable two-wavelength generation in a two chip co-linear T-cavity vertical external-cavity surface-emitting laser

We report the design and experimental results of a two chip co-linear T-cavity vertical external cavity surface emitting laser (VECSEL) capable of generating two continuously tunable orthogonally polarized lasing wavelengths. A polarizing beamsplitter is used to overlap two VECSEL cavities thus generating high-power intra-cavity two-wavelength generation ideal for type-II nonlinear frequency conversion. Nearly equal power at each wavelength with a combined dual-wavelength CW output power in excess of 13 W was observed. In a high Q cavity, the wavelength separation was tuned from 35 nm to 52 nm by using birefringent filters in regions where each wavelength lases independently of the other.

Widely Tunable High-Power Two-Color VECSELs for New Wavelength Generation

We report a collinear two-color vertical external cavity surface emitting laser (VECSEL), which with minimal changes is suitable for intracavity type I second harmonic generation (SHG), type II sum frequency generation (SFG), and type II difference frequency generation (DFG). The demonstrated two-chip cavity provides high-brightness, independently tunable two color, orthogonally polarized intracavity lasing modes. VECSEL chips with emission around 970 and 1185 nm allow the generation of a wide range of wavelengths in the visible and long-wavelength spectral range. The open cavity, collinear geometry, provided a platform for efficient SHG yellow output, SHG blue output, and SFG of green output in the same cavity while only changing the nonlinear crystals. In all cases for visible light generation, a lithium triborate nonlinear crystal is introduced in the cavity region where the fundamental beams are overlapped. Simultaneous SHG and SFG in the same cavity resulting in overlapped outputs consisting of two visible colors are also demonstrated. By using two VECSEL chips with similar gain peaks, intracavity terahertz generation by DFG is demonstrated for the first time in a T-cavity VECSEL geometry. A custom-made tilted periodically poled lithium niobate nonlinear crystal generated DFG signal around 1 THz.

589-nm single-frequency VECSEL for sodium guidestar applications

Here we report on the development and demonstration of a tunable high power single frequency Vertical External Cavity Surface Emitting Laser (VECSEL) operating at 589nm. A highly strained InGaAs/GaAs VECSEL designed to operate at ~ 1178nm is used in conjunction with an intracavity Birefringent Filter (BF) and low finesse Fabry-Perot (FP) etalon to achieve the single frequency operation at the fundamental wavelength. An internal non-linear optical element is then used to obtain the single frequency output at the desired wavelength of 589nm. Our results show outputs in excess of 4W at 589nm with a FWHM linewidth of the fundamental frequency to be less than 10MHz. We demonstrate the measurement of the sodium D1 and D2 lines by passing the output through a reference cell.

Tunable type II intracavity difference frequency generation at 5.4 μm in a two chip vertical external cavity surface emitting laser.

We report on the generation and experimental demonstration of intracavity type II difference frequency generation in a two chip InGaAs/GaAs vertical external cavity surface emitting laser. The presented two chip cavity provides two orthogonally polarized, independently tunable, high-intensity lasing modes with emissions around 970 and 1170 nm. A silver thiogallate nonlinear crystal is inserted in the common collinear folded region of the cavity to generate output in the mid-IR spectral band. The independent tunability of each fundamental color allows for more than 100 nm of tuning around a 5.4 μm difference frequency generated signal with a CW output power in excess of 5 mW.

Tunable type II intracavity sum-frequency generation in a two chip collinear vertical external cavity surface emitting laser

We report on the generation and experimental demonstration of intracavity type II sum-frequency generation (SFG) in a two chip InGaAs/GaAs vertical external cavity surface emitting laser cavity. The demonstrated two-chip cavity generates two orthogonally polarized, independently tunable, high-intensity intracavity lasing modes at different colors. Using a lithium triborate nonlinear crystal in the common collinear folded cavity region, high output power in the blue-green band is generated. Wavelength tuning with CW output powers in excess of 750 mW is demonstrated. By independent wavelength tuning of each fundamental color, tunable SFG output around 490 nm is reported.

Lateral lasing and ASE reduction in VECSELs

Vertical external cavity surface emitting lasers (VECSELs) are attractive for many applications due to their high-power, high-brightness outputs. In order to power scale the devices, the pump spot size should be increased. However, the large pump area greatly amplifies the guided spontaneous emission in the epitaxial plane. In order to efficiently power scale the devices, amplified spontaneous emission (ASE) and lateral lasing must be reduced. We begin by first reporting on the temperature dependence of the phenomena. Particularly, since the quantum well gain and bandgap are functions of temperature, ASE and lateral lasing are greatly dependent on the operating temperature as well as the pump power. The easiest method of quantifying the affect of ASE and lateral lasing is by removing the Fabry-Perot cavity formed by the chip edges. We have chosen two different methods: Reducing the Fresnel reflections by patterning the edges of the sample, and depositing a layer of Ge on the edges of the VECSEL chip as the high index of refraction for Ge should reduce the Fresnel reflections and the absorption properties in the NIR regime should also act to prevent feedback into the pump area. Our research shows both of these methods have increased the performance and visibly decreased the amount of lateral lasing seen in the devices.

Gain coupling of class A semiconductor lasers.

We report on the development of a gain-coupled class A semiconductor laser for dual-wavelength generation via optical switching. A vertical external cavity surface emitting laser (VECSEL) structure is used, because it provides a flexible platform for high-power, high-brightness output in the near-IR and visible ranges. For the first time (to our knowledge), two VECSEL cavities sharing a common gain region are studied. Because the cavities are in competition for common carriers, birefringent filters in the external cavity control the laser cavity thresholds; this configuration demonstrates the possibility of switching between the two cavities, which can operate at different wavelengths. However, in this Letter we also show, numerically and experimentally, that with the consideration of spontaneous emission, it is possible to maintain simultaneous lasing in each cavity at a different wavelength.