Terahertz photometer to observe solar flares in continuum

Solar observations at sub-THz frequencies detected a new flare spectral component peaking in the THz range, simultaneously with the well known microwaves component, bringing challenging constraints for interpretation. Higher THz frequencies observations are needed to understand the nature of the mechanisms occurring in flares. A THz photometer system was developed to observe outside the terrestrial atmosphere on stratospheric balloons or satellites, or at exceptionally transparent ground stations. The telescope was designed to observe the whole solar disk detecting small relative changes in input temperature caused by flares at localized positions. A Golay cell detector is preceded by low-pass filters to suppress visible and near IR radiation, a band-pass filter, and a chopper. A prototype was assembled to demonstrate the new concept and the system performance. It can detect temperature variations smaller than 1 K for data sampled at a rate of 10/second, smoothed for intervals larger than 4 seconds. For a 76 mm aperture, this corresponds to small solar burst intensities at THz frequencies. A system with 3 and 7 THz photometers is being built for solar flare observations on board of stratospheric balloon missions.Comment: 11 pages, 8 figures, accepted by Journal of Infrared, Millimeter, and Terahertz Waves, 9 December 201

Metal mesh resonant filters or terahertz frequencies

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)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 3THz. (c) 2008 Optical Society of America473260646069Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Argentina agency Consejo Nacional de Investigaciones Cientfficas y Tecnicas (CONICET)Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq

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 roomtemperature 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 subsecond 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.7012Stein, W.A., Ney, E.P., (1963) J. Geophys. Res., 68, p. 65Shlovsky, J., (1964) Nature, 202, p. 275Najita, K., Orrall, F.Q., (1970) Solar Phys., 15, p. 176Ohki, K., Hudson, H.S., (1975) Solar Phys., 43, p. 405Hachenberg., O., Wallis, G., (1961) Z.Astrophys., 52, p. 42Croom, D.L., (1970) Solar Phys., 15, p. 414Shimabukuro, F.I., (1970) Solar Phys., 15, p. 424Cogdell, J.R., (1972) Solar Phys., 22, p. 147Akabane, K., (1973) Solar Phys., 33, p. 431Kaufmann, P., (1985) Nature, 313, p. 380Ramaty, R., (1994) Astrophys. J., 435, p. 941Clark, C.D., Park, W.M., (1968) Nature, 219, p. 922Beckman, J.E., (1968) Nature, 220, p. 52Hudson, H.S., (1975) Solar Phys., 45, p. 69Kaufmann, E., A new look of the Sun (1994) Proc. Kofu Symposium, p. 323. , NRO Report nr. 360Kaufmann, P., (2001) Proc. SBMO/IEEE MTT-S Int.Microwave and Optoelectronics Conf., p. 439. , Ed. By J.T. Pinho, G.P.S. Cavalcante and L.A.H.G. Oliveira, IEEE, PiscatawayMelo, A.M., (2006) Publ. Astron. Soc. Pacific, 118, p. 1558Marcon, R., (2008) Publ. Astron. Soc. Pacific, 120, p. 863Martin, R.N., Kingsley, J.S., Kingsley, R.K., SPIE Proc. on Advanced Technology MMW Radio and Terahertz Telescopes, 3357 (721), pp. 1998.. , Ed. by T.G. PhillipsGeorges, C.B., 2nd. SBMO (1989) Intl. Microwave Symp., 2, p. 447. , IEEE cat. no. 89TH0260De Castro, C.G.G., (1999) Astron Astrophys., 140, p. 373Melo, A.M., (2005) IEEE Trans. Ant. Propagat., 53, p. 1528Costa, J.E.R., (2002) Astron.Astrophys., 387, p. 1153Wallace, P.T., Tpoint Technical Report TPS/06/11/SST, pp. 2006.Kaufmann, P., (2001) Astrophys. J., 548, pp. L95Trottet, (2002) Astron.Astrophys., 694, p. 381Kaufmann, P., (2002) Astrophys.J., 574, p. 1059Raulin, J.-P., (2003) Astrophys. J., 592, p. 580Kaufmann, P., (2003) J.Geophys. Res., 108. , DOI 10.1029/2002JA009729Silva, A., (2005) Solar Phys., 227, p. 264Kaufmann, P., (2004) Astrophys. J., 603, pp. L121Silva, (2007) Solar Phys., 227, p. 265Kaufmann, P., (2007) American Astronomical Society Meeting 210, pp. 93.30Kaufmann, P., (2008) 1st SMESE Workshop, Paris, , http://www.ias.u-psud.fr/smese/schedule-1st.php, 10-12 MarchLindsey, C., Hudson, H.S., (1976) Astrophys.J, 203, p. 753Vial, J.-C., (2008) Adv.Space Sci., 41, p. 183Kaufmann, P., (2006) SIRA research proposal, , submitted to Brazilian agencie