Nir Dahan

Space-variant polarization manipulation of a thermal emission by a SiO2 subwavelength grating supporting surface phonon-polaritons

Space-variant polarization manipulation of thermal emission in a narrow spectral-peak is presented. The emission is attributed to surface phonon-polariton excitation from space-variant subwavelength SiO/sub 2/ gratings. We experimentally demonstrated thermal emission in an axially symmetric polarization distribution.

Highly coherent thermal emission obtained by plasmonic bandgap structures

We demonstrate an extraordinary quasimonochromatic thermal emission with high spatial coherence length (lc>2400λ) and a quality factor Q=2320 at radiation frequencies that are much smaller than the plasma frequency of metal (ω≪ωp). This emission is achieved by forming a plasmonic bandgap, which is obtained by a periodic structure on a metallic surface. Such a structure modifies the dynamics of the surface wave and results in a van Hove singularity [Van Hove, Phys. Rev. 89, 1189 (1953)] in the spectral density of states while maintaining a large coherence length.

Extraordinary Coherent Thermal Emission From SiC Due to Coupled Resonant Cavities

In high temperature and vacuum applications, when heat transfer is predominantly by radiation, the material’s surface texture is of substantial importance. Several micro- and nanostructure designs have been proposed to enhance a material’s emissivity and its radiative coherence, as control of thermal emission is of crucial concern in the design of infrared sources, optical filters, and sensing devices. In this research, an extraordinary coherent thermal emission from an anisotropic microstructure is experimentally and theoretically presented. The enhanced coherency is due to coherent coupling between resonant cavities obtained by surface standing waves, wherein each cavity supports a localized field that is attributed to coupled surface phonon polaritons. We show that it is possible to obtain a polarized quasimonochromatic thermal source from a SiC microstructure with a high quality factor of 600 at the resonant frequency of the cavity and a spatial coherence length of 716 wavelengths, which corresponds to an angular divergence of 1.4 mrad. In the experimental results, we measured a quality factor of 200 and a spatial coherence length of 143 wavelengths. We attribute the deviation in the experimental results to imperfections in the fabrication of the high quality factor cavities. DOI: 10.1115/1.2955475

Slow surface phonon polaritons for sensing in the midinfrared spectrum

We demonstrate a reflection-type sensor in the midinfrared spectra based on resonant excitation of surface phonon polaritons (SPhPs). In this range, SPhPs are characterized by the high density of states associated with slow surface waves that lead to enhanced resonance absorption. Delocalized SPhPs were excited by irradiating TM-polarized light on a one-dimensional grating embedded in a SiC substrate. The sensor response was characterized by changing the refractive index (RI) of a lossless CO2 gas. A detection limit of 2×10−5 RI units was obtained at a wavelength of 11.9 μm.

Thermal image encryption obtained with a SiO 2 space-variant subwavelength grating supporting surface phonon-polaritons

Space-variant partially polarized thermal emission is investigated. We show that by coupling surface phonon-polaritons to a propagating field, large anisotropy of the emissivity is obtained within a narrow spectral range. We experimentally demonstrate this effect by fabricating a space-variant subwavelength grating on a SiO2 substrate to encrypt an image in the polarization state of a thermal radiation field.

Bandgap structure of thermally excited surface phonon polaritons

A wide bandgap of thermally excited surface phonon polaritons (SPhPs) is experimentally observed. Formation of the bandgap and coupling to radiative waves is done by a binary biharmonic structure formed on a SiC substrate. The bandgap width is controlled by the ratio of the two harmonic magnitudes of the structure’s profile. The characteristic one-dimensional Van Hove singularity is experimentally observed in the spectral density of states of the SPhPs. Moreover, an inverse relation is found between the gap width and the squared spatial coherence length of the emitted thermal radiation, as predicted by theoretical calculations.

Space-variant polarization manipulation of a thermal emission by a SiO/sub 2/ subwavelength grating supporting surface phonon-polariton

Space-variant polarization manipulation of thermal emission in a narrow spectral-peak is presented. The emission is attributed to surface phonon-polariton excitation from space-variant subwavelength SiO/sub 2/ gratings. We experimentally demonstrated thermal emission in an axially symmetric polarization distribution.

Low-NA fiber laser pumps powered by high-brightness single emitters

Fiber laser manufacturers demand high-brightness laser diode pumps delivering optical pump energy in both a compact fiber core and narrow angular content. A pump delivery fiber of a 105 μm core and 0.22 numerical aperture (NA) is typically used, where the fiber NA is under-filled to ease the launch of laser diode emission into the fiber and make the fiber tolerant to bending. At SCD, we have developed high-brightness NEON multi-emitter fiber-coupled pump modules that deliver 50 W output from a 105 μm, 0.15 NA fiber enabling low-NA power delivery to a customer’s fiber laser network. Brightness-enhanced single emitters are engineered with ultra-low divergence for compatibility with the low-NA delivery fiber, with the latest emitters delivering 14 W with 95% of the slow-axis energy contained within an NA of 0.09. The reduced slow-axis divergence is achieved with an optimized epitaxial design, where the peak optical intensity is reduced to both lessen filamentation within the laser cavity and reduce the power density on the output facet thus increasing the emitter reliability. The low mode filling of the fiber allows it to be coiled with diameters down to 70 mm at full operating power despite the small NA and further eliminates the need for mode-stripping at fiber combiners and splices downstream from our pump modules. 50W fiber pump products at 915, 950 and 975 nm wavelengths are presented, including a wavelengthstabilized version at 976 nm.

High-brightness 800nm fiber-coupled laser diodes

Fiber-coupled laser diodes have become essential sources for fiber laser pumping and direct energy applications. Single emitters offer reliable multi-watt output power from a 100 m lateral emission aperture. By their combination and fiber coupling, pump powers up to 100 W can be achieved from a low-NA fiber pigtail. Whilst in the 9xx nm spectral range the single emitter technology is very mature with <10W output per chip, at 800nm the reliable output power from a single emitter is limited to 4 W – 5 W. Consequently, commercially available fiber coupled modules only deliver 5W – 15W at around 800nm, almost an order of magnitude down from the 9xx range pumps. To bridge this gap, we report our advancement in the brightness and reliability of 800nm single emitters. By optimizing the wafer structure, laser cavity and facet passivation process we have demonstrated QCW device operation up to 19W limited by catastrophic optical damage to the 100 μm aperture. In CW operation, the devices reach 14 W output followed by a reversible thermal rollover and a complete device shutdown at high currents, with the performance fully rebounded after cooling. We also report the beam properties of our 800nm single emitters and provide a comparative analysis with the 9xx nm single emitter family. Pump modules integrating several of these emitters with a 105 μm / 0.15 NA delivery fiber reach 35W in CW at 808 nm. We discuss the key opto-mechanical parameters that will enable further brightness scaling of multi-emitter pump modules.

Manipulation of a Thermal Emission by Use of Micro- and Nanoscale Structures

In high temperature and vacuum applications, when heat transfer is predominantly by radiation, the material’s surface texture is of substantial importance. Several micro and nanostructures designs have been proposed to enhance a material’s emissivity and its radiative coherence, as control of thermal emission is of crucial concern in the design of infrared sources, in electronic chip coolants, in high-efficiency photovoltaic cells, and in solar energy conversion.Copyright