During the dawn of chemistry
, when the temperature of the young Universe had fallen below some 4,000 kelvin, the ions of the light elements produced in Big Bang nucleosynthesis recombined in reverse ...order of their ionization potential. With their higher ionization potentials, the helium ions He
and He
were the first to combine with free electrons, forming the first neutral atoms; the recombination of hydrogen followed. In this metal-free and low-density environment, neutral helium atoms formed the Universe's first molecular bond in the helium hydride ion HeH
through radiative association with protons. As recombination progressed, the destruction of HeH
created a path to the formation of molecular hydrogen. Despite its unquestioned importance in the evolution of the early Universe, the HeH
ion has so far eluded unequivocal detection in interstellar space. In the laboratory the ion was discovered
as long ago as 1925, but only in the late 1970s was the possibility that HeH
might exist in local astrophysical plasmas discussed
. In particular, the conditions in planetary nebulae were shown to be suitable for producing potentially detectable column densities of HeH
. Here we report observations, based on advances in terahertz spectroscopy
and a high-altitude observatory
, of the rotational ground-state transition of HeH
at a wavelength of 149.1 micrometres in the planetary nebula NGC 7027. This confirmation of the existence of HeH
in nearby interstellar space constrains our understanding of the chemical networks that control the formation of this molecular ion, in particular the rates of radiative association and dissociative recombination.
Phase gratings are used as beam multiplexers in the submillimeter and Terahertz spectral range. Two-dimensional beam arrangements can often be obtained most easily by the superposition of two ...one-dimensional grating structures. We show that in general this approach does not yield the maximum grating efficiency and propose a method to obtain significantly higher efficiencies for this grating class.
Abstract
Atomic oxygen is a key species in the mesosphere and thermosphere of Venus. It peaks in the transition region between the two dominant atmospheric circulation patterns, the retrograde ...super-rotating zonal flow below 70 km and the subsolar to antisolar flow above 120 km altitude. However, past and current detection methods are indirect and based on measurements of other molecules in combination with photochemical models. Here, we show direct detection of atomic oxygen on the dayside as well as on the nightside of Venus by measuring its ground-state transition at 4.74 THz (63.2 µm). The atomic oxygen is concentrated at altitudes around 100 km with a maximum column density on the dayside where it is generated by photolysis of carbon dioxide and carbon monoxide. This method enables detailed investigations of the Venusian atmosphere in the region between the two atmospheric circulation patterns in support of future space missions to Venus.
Abstract
We report NASA-DLR SOFIA upGREAT circumstellar O
i
63.2
μ
m and C
ii
157.7
μ
m emission profiles and FIFI-LS O
i
63.2
μ
m, O
i
145.5
μ
m, and C
ii
157.7
μ
m fluxes obtained shortly ...after Betelgeuse’s 2019/2020 Great Dimming event. Haas et al. noted a potential correlation between the O
i
63.2
μ
m flux and
V
magnitude based on three Kuiper Airborne Observatory observations made with the CGS and FIFI instruments. The FIFI observation was obtained when V ≃ 0.88 and revealed a 3
σ
non-detection at a quarter of the previous CGS flux measurement made when
V
≃ 0.35. A potential explanation could be a change in dust-gas drag heating by circumstellar silicates caused by variations in the photospheric radiation field. SOFIA observations provide a unique test of this correlation because the
V
-band brightness went to its lowest value on record,
V
≃ 1.61, with the SOFIA observations being made when
V
FIFI−LS
≃ 1.51 and
V
upGREAT
≃ 1.36. The upGREAT spectra show a O
i
63.2
μ
m flux larger than previous space observatory measurements obtained when
V
≃ 0.58. The profile is consistent with formation in the slower, more turbulent inner S1 outflow, while the C
ii
157.7
μ
m profile is consistent with formation farther out in the faster S2 outflow. Modeling of dust-gas drag heating, combined with 25 yr of Wing three-filter and
V
photometry, reveals that it is unlikely that the S1 circumstellar envelope and O
i
63.2
μ
m fluxes are dominated by the dust-gas drag heating and that another heating source is also active. The O
i
63.2
μ
m profile is hard to reconcile with existing outflow velocity models.
GaAs/AlGaAs quantum cascade lasers based on four quantum well structures operating at 4.7 THz are reported. A large current density dynamic range is observed, leading to a maximum operation ...temperature of 150 K for the double metal waveguide device and a high peak output power more than 200 mW for the single surface plasmon waveguide device. A continuous wave, single mode, third order distributed feedback laser with a low electrical power dissipation and a narrow far-field beam pattern, which is required for a local oscillator in astronomy heterodyne spectrometers, is also demonstrated.
A Compact Beam Measurement Setup Graf, Urs U.
Journal of infrared, millimeter and terahertz waves,
08/2016, Letnik:
37, Številka:
8
Journal Article
Recenzirano
Odprti dostop
We present the design of a compact measurement device to determine the position of a beam in a radio optical setup. The unit is used to align the Terahertz optics of the GREAT instrument on the ...airborne astronomical observatory SOFIA.
Astronomical heterodyne spectrometers, such as upGREAT on the SOFIA telescope, use a powerful quantum cascade laser (QCL) as local oscillator (LO) to observe the atomic oxygen line at 4.7 THz. The ...free-running laser, although temperature stabilized, is prone to broad effective linewidth and frequency drifts and lacks an absolute frequency reference. In this work, our successful frequency locking of a 4.7 THz QCL by employing a delay line as a means of frequency discrimination is presented. We use a subharmonically pumped superlattice mixer to downconvert the QCL signal to approximately 400 MHz. From this signal the delay line frequency discriminator produces an error signal, which is fed back to the QCL supply current to correct the frequency instabilities. Our method reduces the laser linewidth from 10 MHz in free running mode to 780 kHz when locked. The locking scheme is robust and has been demonstrated to operate down to signal to noise conditions as low as 2 dB.
Terahertz Heterodyne Array Receivers for Astronomy Graf, Urs U.; Honingh, Cornelia E.; Jacobs, Karl ...
Journal of infrared, millimeter and terahertz waves,
10/2015, Letnik:
36, Številka:
10
Journal Article
Recenzirano
Odprti dostop
We review the development of multi-pixel heterodyne receivers for astronomical research in the submillimeter and terahertz spectral domains. We shortly address the historical development, ...highlighting a few pioneering instruments. A discussion of the design concepts is followed by a presentation of the technologies employed in the various receiver subsystems and of the approaches taken to optimize these for current and future instruments.
We present the upGREAT THz heterodyne arrays for far-infrared astronomy. The low-frequency array (LFA) is designed to cover the 1.9-2.5 THz range using 2 × 7-pixel waveguide-based HEB mixer arrays in ...a dual polarization configuration. The high-frequency array (HFA) will perform observations of the OI line at ~ 4.745 THz using a 7-pixel waveguide- based HEB mixer array. This paper describes the common design for both arrays, cooled to 4.5 K using closed-cycle pulse tube technology. We then show the laboratory and telescope characterization of the first array with its 14 pixels (LFA), which culminated in the successful commissioning in May 2015 aboard the SOFIA airborne observatory observing the CII fine structure transition at 1.9005 THz. This is the first successful demonstration of astronomical observations with a heterodyne focal plane array above 1 THz and is also the first time high-power closed-cycle coolers for temperatures below 4.5 K are operated on an airborne platform.
4GREAT is an extension of the German receiver for astronomy at terahertz frequencies (GREAT) operated aboard the Stratospheric Observatory for Infrared Astronomy (SOFIA). The spectrometer comprises ...four different detector bands and their associated subsystems for simultaneous and fully independent science operation. All detector beams are coaligned on the sky. The frequency bands of 4GREAT cover 491-635, 890-1090, 1240-1525, and 2490-2590 GHz, respectively. This article presents the design and characterization of the instrument, and its in-flight performance. The first light of 4GREAT was on June 2018. It has been offered to the interested SOFIA communities starting with observing cycle 6.
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