Arline M. Melo

Metal mesh resonant filters for terahertz frequencies

The interest in terahertz photometric and imaging measurements has motivated the development of bandpass resonant filters to be coupled to multiple-pixel devices such as bolometer arrays. Resonant grids are relatively simple to fabricate, exhibiting high transmission at the central frequency, a narrow bandpass, and good rejection of the side frequencies of the spectrum. We have fabricated filters centered at different frequencies between 0.4 and 10 THz, using photolithography and electroforming techniques. Transmission measurements have shown center frequencies and bandwidths close to the design predictions. The performance of the filters was found not to be critically dependent on small physical deformations in the mesh, becoming more noticeable at higher frequencies (i.e., for smaller physical sizes). Wider bandwidths, needed to attain higher sensitivities in the continuum, were obtained by changing the design parameters for filters at 2 and 3 THz.

Cross-Shaped Terahertz Metal Mesh Filters: Historical Review and Results

Terahertz frequencies experiments has motivated the development of new sources, detectors and optical components. Here we will present a review of THz bandpass filters ranging from 0.4 to 10 THz. We also demonstrate our fabrication process, simulations and experimental results.

New telescopes for ground-based solar observations at submillimeter and mid-infrared

The solar submillimeter-wave telescope (SST) is the only one of its kind dedicated to solar continuous observations. Two radiometers at 0.740 mm (405 GHz), and four at 1.415 mm (212 GHz) are placed in the Cassegrain focal plane of the 1.5-m dish at El Leoncito high altitude site, San Juan, Argentina. The aperture efficiencies are close to design predictions: 20% and 35% for 2 and 4 arcminutes beam sizes at 405 and 212 GHz, respectively. The positioner absolute pointing accuracy is 10 arcseconds. Spectral coverage is complemented by ground-based mid-infrared telescopes developed for high cadence observations in the continuum 10 micron band (30 THz), using small apertures and room-temperature microbolometer cameras. Using the system, a new solar burst spectral component was discovered, exhibiting fluxes increasing for smaller wavelengths, separated from the well known microwave component. Rapid sub-second pulsations are common for all bursts. The pulsations onset times of appear to be connected to the launch times of CMEs. Active regions are brighter for shorter submillimeter-waves. Mid-IR bright regions are found closely associated with calcium plages and magnetic structures near the solar photosphere. Intense and rapid 10 micron brightening was detected on active centers in association with weak flares. These results raise challenging difficulties for interpretation.

Imaging at 0.2 and 2.5 terahertz

We report the development and initial results of two Terahertz imaging systems based on monochromatic sources at 0.2 and 2.52 THz. The first is based on a microwave oscillator, whose frequency is multiplied to 0.2 THz, used in conjunction with a zero-bias detector. The sample is scanned across the beam, and transmission images are obtained after processing. The second system allows real-time images, and consists of a methanol gas laser emitting at 119 microns (2.52 THz) and a commercial camera based on a microbolometer array. We describe the construction and performance of the methanol laser and a tunable CO2 laser, which emits 20 W at the 9P(36) pump line. Due to the high coherence of the laser, this system is particularly suited for diffraction and interference imaging. We have measured the absorption coefficients of a few samples assuming the Beer law.

Imaging with monochromatic sources at 0.2 and 2.5 TeraHertz

We describe the design and construction of two Terahertz imaging systems based on sources at 0.2 and 2.52 THz. One is based on a single emitter and detector, in which the sample position is scanned across the beam. The other is based on a molecular gas laser at 2.52 THz and a microbolometer camera.

Micromachined Structures Used in DNA Damages Response Studies

Micromachined sieves structures were manufactured to be used as thin microaperture system for localized induction of DNA damage in living cells using ultra-soft X-rays. The lithography fabrication of such structures is described in this paper.

Concept of partially overlapping multiple beams for spatial determination of solar bursts time transients at submm-IR wavelengths

The concept of partially overlapping multiple beams, produced by focal plane arrays in large antennas, has been used successfully at mm-waves to detect instantaneously spatial positions of rapid spikes produced by solar flares. The technique has been used at mm-waves and was recently applied to the Solar Submillimeter-wave Telescope, which operates at 212 and 405 GHz. We present the basic description of the concept and the results obtained. New applications are being considered for shorter submm-IR wavelengths, with the use of focal plane arrays of bolometers, which spatial angular accuracy will strongly depend on the knowledge of the beamshapes of the individual beams produced.