Infrared Metasurfaces Created with Off-Normal Incidence Microsphere Photolithography

Fabricating metasurfaces over large areas at low costs remains a critical challenge to their practical implementation. This paper reports on the use of microsphere photolithography (MPL) to create infrared metasurfaces by changing the angle-of-incidence of the illumination to steer the photonic jet. The displacement of the photonic jet is shown to scale with the diameter of the microsphere while the exposure dose scales with the square of the microsphere diameter. This process is robust in the presence of local defects in the microsphere lattice. The paper demonstrates patterning split ring resonators and tripole based metasurfaces using MPL, which are fabricated and characterized with FTIR. The combination of bottom-up and top-down approaches in off-normal incidence microsphere photolithography technique provides cost-effective, flexible, and high-throughput fabrication of infrared metasurfaces

Near Field Transducer for Heat Assisted Magnetic Recording

An antenna for heat assisted magnetic recording is disclosed. The antenna includes an optically opaque material and an optically transparent material positioned on the optically opaque material, the optically transparent material includes a half bowtie shape which includes a first half-wing substantially shaped in form of a right angle trapezoid, having a height substantially equal to the overall height of the half bowtie, a second half-wing Substantially shaped in form of a mirror image of the first half-wing and formed proximate and coupled to the first half-wing by a Substantially rectangular aperture having an aperture width and an aperture height. The aperture height is as Small as 1 nm

Frequency-Selective Metasurface Integrated Uncooled Microbolometers

A metasurface integrated microbolometer having a sensing layer (e.g., SixGeyO1-x-y). The presence of the metasurface provides selectivity with respect to wavelength, polarization and angle-of-incidence. The presence of the metasurface into the microbolometer affects conversion of electromagnetic to thermal energy, thermal response, electrical integration of the microbolometer, and the tradeoff between resistivity and temperature coefficient of resistance, thereby allowing the ability to obtain a sensing with high temperature coefficient of resistance with lower resistivity values than that of films without the metasurface. The presence of the metasurface removes the need for a Fabry-Perot cavity

In-situ Lock-in Thermographic Measurement Of Powder Layer Thermal Diffusivity And Thickness In Laser Powder Bed Fusion

The thermal transport properties of the powder layer play a crucial role in the process of laser powder bed fusion (LPBF). This paper introduces an in-situ measurement method utilizing active lock-in infrared thermography (LIT) to determine the thermal diffusivity and thickness of the powder layer. The proposed method exhibits great potential for accurate powder property and thickness measurements and real-time process monitoring. In this lock-in thermographic technique, the LPBF laser beam is directed through an optical diffuser and modulated into a square thermal wave. This thermal wave serves as an active heat source to heat the surface of the powder bed. The surface temperature response is captured using a long-wave infrared (LWIR) camera. A one-dimensional thermal model is employed to provide insights into heat transfer in the frequency domain. The frequency-dependent phase response of temperature is influenced by the effective thermal diffusivity and thickness of the powder layer. This model is validated experimentally first and then utilized to measure the thermal diffusivity of different powder layers created using various particle sizes and wiper spreading speeds. Larger particle size and slower wiper spreading speed are shown to produce higher thermal diffusivity. Finally, the paper shows how this technique can be used to measure the powder layer thickness over printed geometries. This capability enables the detection of deviations in the fused part surface or errors in the wiper through analysis of resulting variations in the powder. These findings highlight the potential of the lock-in thermographic technique for rapid in-situ inspection of the new powder layer in laser powder bed fusion (LPBF) processes

Extraordinary infrared transmission through a periodic bowtie aperture array,” Opt

The discovery of extraordinary transmission through periodic aperture arrays has generated significant interest. Most studies have used circular apertures and attributed enhanced transmission to surface plasmon polariton (SPP) resonances and/or Rayleigh-Wood anomalies (RWA). Bowtie apertures concentrate light and have much longer cutoff wavelengths than circular apertures and can be designed to be strongly resonant. We demonstrate here that the total transmission through a bowtie aperture array can exceed 85% (4ϫ the open area). Furthermore, we show that the high transmission is due to waveguide modes as opposed to the commonly believed SPP/RW phenomena. This work is focused on IR wavelengths near 9 m; however, the results are broadly applicable and can be extended to optical frequencies. © 2010 Optical Society of America OCIS codes: 240.0240, 240.6680, 050.1220. Classical aperture theory predicts that transmission through a subwavelength hole scales with ͑d / ͒ 4 , where d is the diameter of the aperture and is the free-space wavelength of light In this Letter we investigate transmission through a periodic array of bowtie apertures. The transmission modes are optimized to obtain high transmission around =9 m. The high transmission in IR has the potential as a high-efficiency IR coupler for detection devices. The bowtie aperture is also polarization selective, therefore useful where polarization selectivity is of interest such as IR polarimetry imaging Bowtie apertures are one type of ridge aperture The geometry of the bowtie aperture array studied in this work is shown in 992 OPTICS LETTERS / Vol. 35

Distributed Optical Fiber Testing for Additive Manufacturing

This paper explores optical fiber's use for in-situ inspection of additive manufacturing. Single-mode SMF-28 optical fiber can be placed on the build plate to monitor the printing process or embedded in the part. Distributed measurements using optical backscattering reflectometry (OBR) resolve the strain along the optical fiber and the temperature. OBR-enabled sensing is demonstrated for the fused filament fabrication (FFF) process. The small diameter (0.125 mm) of SMF-28 lends itself to embedding in FFF prints. This enables laying the fiber into the part, which provides continued sensing for the details in use. Knowledge of the process and the fiber arrangement allows heating from the deposition head to be distinguished from stress-driven strain. Calibration of the fiber arrangement is discussed, as well as a comparison with process modeling.Mechanical Engineerin

Toward DMD Illuminated Spatial-Temporal Modulated Thermography

This paper reports on a system using a Digital Micromirror Device (DMD) to modulate a near-infrared laser source spatially and temporally. The DMD can produce an arbitrary heat source varying both spatially and temporally over the target. When the thermal response of the target surface is recorded using a thermal imager, this provides new possibilities in subsurface defect detection, partially with regard to features whose orientation does not allow them to be resolved using conventional thermographic inspection techniques. In this respect it is similar to conventional focused spot detection approaches; however, the DMD allows the signal to be frequency/phase multiplexed which provides for simultaneous interrogation over a large area. The parallel nature of the process permits a longer inspection time at each point which has signal-to-noise benefits. Preliminary experiments demonstrating the multiplexing approach are presented using a low-cost thermal imager. A NIR laser is spatially and temporary modulated to generated multiple thermal line sources on the surface of a composite circuit board. The infrared response is demodulated point-by-point at each drive frequency. This permits the thermal response from each line source to be resolved individually. Beyond damage detection the approach also has applications to system identification. Initial limitations due to the test setup are discussed along with future system improvements

Thermal Stress Prediction in Laser Powder Bed Fusion

This research applies Green's function solutions to simulate temperature and thermal stress fields in laser powder-bed fusion (LPBF) processes. Using a semi-infinite domain and 2D Gaussian laser profiles, the analytical model achieves high computational efficiency, has the potential for realtime controls and predictions in LPBF processes. The model highlights the role of principal stresses in determining crack formations, aligning closely with experimental results.Mechanical Engineerin

Experimental Investigation of Condensation Phenomenon on Hydrophilic and Hydrophobic Titanium (Ti) Pillared Glass Surfaces

Atmospheric condensation is very important for multiple practical applications such as heat transfer, aerospace, and water harvesting etc. Surfaces below the dew point temperature, heterogeneously nucleate water droplets on the surfaces. Gibbs free energy of heterogeneous nucleation barrier for a condensed droplet on a rough surface changes significantly with the change of humidity content. The influence of environmental factors and substrate characteristics (topology, surface chemistry, and substrate temperature) on atmospheric condensation is very important to elucidate the droplet shape and wetting state. Condensation from the humid air has been studied on Titanium (Ti) pillars and Teflon© coated Ti pillared glass surfaces in order to reveal the condensate harvesting and dropwise condensation applications