451 research outputs found
Surface wave control for large arrays of microwave kinetic inductance detectors
Large ultra-sensitive detector arrays are needed for present and future
observatories for far infra-red, submillimeter wave (THz), and millimeter wave
astronomy. With increasing array size, it is increasingly important to control
stray radiation inside the detector chips themselves, the surface wave. We
demonstrate this effect with focal plane arrays of 880 lens-antenna coupled
Microwave Kinetic Inductance Detectors (MKIDs). Presented here are near field
measurements of the MKID optical response versus the position on the array of a
reimaged optical source. We demonstrate that the optical response of a detector
in these arrays saturates off-pixel at the dB level compared to the
peak pixel response. The result is that the power detected from a point source
at the pixel position is almost identical to the stray response integrated over
the chip area. With such a contribution, it would be impossible to measure
extended sources, while the point source sensitivity is degraded due to an
increase of the stray loading. However, we show that by incorporating an
on-chip stray light absorber, the surface wave contribution is reduced by a
factor 10. With the on-chip stray light absorber the point source response
is close to simulations down to the dB level, the simulation based on
an ideal Gaussian illumination of the optics. In addition, as a crosscheck we
show that the extended source response of a single pixel in the array with the
absorbing grid is in agreement with the integral of the point source
measurements.Comment: accepted for publication in IEEE Transactions on Terahertz Science
and Technolog
Eliminating stray radiation inside large area imaging arrays
With increasing array size, it is increasingly important to control stray
radiation inside the detector chips themselves. We demonstrate this effect with
focal plane arrays of absorber coupled Lumped Element microwave Kinetic
Inductance Detectors (LEKIDs) and lens-antenna coupled distributed quarter
wavelength Microwave Kinetic Inductance Detectors (MKIDs). In these arrays the
response from a point source at the pixel position is at a similar level to the
stray response integrated over the entire chip area. For the antenna coupled
arrays, we show that this effect can be suppressed by incorporating an on-chip
stray light absorber. A similar method should be possible with the LEKID array,
especially when they are lens coupled.Comment: arXiv admin note: substantial text overlap with arXiv:1707.0214
Modeling and Testing Superconducting Artificial CPW Lines Suitable for Parametric Amplification
Achieving amplification with high gain and quantum-limited noise is a
difficult problem to solve. Parametric amplification using a superconducting
transmission line with high kinetic inductance is a promising technology not
only to solve this problem but also adding several benefits. When compared with
other technologies, they have the potential of improving power saturation,
achieving larger fractional bandwidths and operating at higher frequencies. In
this type of amplifiers, selecting the proper transmission line is a key
element in their design. Given current fabrication limitations, traditional
lines such as coplanar waveguides (CPW), are not ideal for this purpose since
it is difficult to make them with the proper characteristic impedance for good
matching and slow-enough phase velocity for making them more compact.
Capacitively-loaded lines, also known as artificial lines, are a good solution
to this problem. However, few design rules or models have been presented to
guide their accurate design. This fact is even more crucial considering that
they are usually fabricated in the form of Floquet lines that have to be
designed carefully to suppress undesired harmonics appearing in the parametric
process. In this article we present, firstly, a new modelling strategy, based
on the use of electromagnetic-simulation software, and, secondly, a
first-principles model that facilitate and speed the design of CPW artificial
lines and of Floquet lines made out of them. Then, we present comparisons with
experimental results that demonstrate their accuracy. Finally, the theoretical
model allows to predict the high-frequency behaviour of the artificial lines
showing that they are good candidates for implementing parametric amplifiers
above 100 GHz.Comment: 7 pages, 11 figures, submitted to IEEE Transactions on Applied
Superconductivit
Mucosal and Systemic Immune Responses to Salmon Gill Poxvirus Infection in Atlantic Salmon Are Modulated Upon Hydrocortisone Injection
Salmon Gill Poxvirus Disease (SGPVD) has emerged as a cause of acute mortality in Atlantic salmon (Salmo salar L.) presmolts in Norwegian aquaculture. The clinical phase of the disease is associated with apoptotic cell death in the gill epithelium causing acute respiratory distress, followed by proliferative changes in the regenerating gill in the period after the disease outbreak. In an experimental SGPV challenge trial published in 2020, acute disease was only seen in fish injected with hydrocortisone 24 h prior to infection. SGPV-mediated mortality in the hydrocortisone-injected group was associated with more extensive gill pathology and higher SGPV levels compared to the group infected with SGPV only. In this study based on the same trial, SGPV gene expression and the innate and adaptive antiviral immune response was monitored in gills and spleen in the presence and absence of hydrocortisone. Whereas most SGPV genes were induced from day 3 along with the interferon-regulated innate immune response in gills, the putative SGPV virulence genes of the B22R family were expressed already one day after SGPV exposure, indicating a potential role as early markers of SGPV infection. In gills of the hydrocortisone-injected fish infected with SGPV, MX expression was delayed until day 10, and then expression skyrocketed along with the viral peak, gill pathology and mortality occurring from day 14. A similar expression pattern was observed for Interferon gamma (IFNγ) and granzyme A (GzmA) in the gills, indicating a role of acute cytotoxic cell activity in SGPVD. Duplex in situ hybridization demonstrated effects of hydrocortisone on the number and localization of GzmA-containing cells, and colocalization with SGPV infected cells in the gill. SGPV was generally not detected in spleen, and gill infection did not induce any corresponding systemic immune activity in the absence of stress hormone injection. However, in fish injected with hydrocortisone, IFNγ and GzmA gene expression was induced in spleen in the days prior to acute mortality. These data indicate that suppressed mucosal immune response in the gills and the late triggered systemic immune response in the spleen following hormonal stress induction may be the key to the onset of clinical SGPVD
Theory of coherent acoustic phonons in InGaN/GaN multi-quantum wells
A microscopic theory for the generation and propagation of coherent LA
phonons in pseudomorphically strained wurzite (0001) InGaN/GaN multi-quantum
well (MQW) p-i-n diodes is presented. The generation of coherent LA phonons is
driven by photoexcitation of electron-hole pairs by an ultrafast Gaussian pump
laser and is treated theoretically using the density matrix formalism. We use
realistic wurzite bandstructures taking valence-band mixing and strain-induced
piezo- electric fields into account. In addition, the many-body Coulomb
ineraction is treated in the screened time-dependent Hartree-Fock
approximation. We find that under typical experimental conditions, our
microscopic theory can be simplified and mapped onto a loaded string problem
which can be easily solved.Comment: 20 pages, 17 figure
Proof-of-Concept Demonstration of Vector Beam Pattern Measurements of Kinetic Inductance Detectors
We present results from the first vector beam pattern measurement ofmicrowave kinetic inductance detectors (MKIDs). Vector beam patterns require sampling of the E-field of the receiver in both amplitude and phase. MKIDs are inherently direct detectors and have no phase response to incoming radiation. We map the amplitude and phase patterns of the detector beam profile by adapting a two-source heterodyne technique. Our testing strategy recovers the phase information by creating a reference signal to trigger data acquisition. The reference is generated by mixing the slightly offset low-frequency signals from the output of the two synthesizers used to drive the submillimeter sources. The key requirement is that the time-series record always begins at the same set phase of the reference signal. As the source probe is scanned within the receiver beam, the wavefront propagation phase of the receiver changes and causes a phase offset between the detector output and reference signals. We demonstrated this technique on the central pixel of a test array operating at 350 GHz. This methodology will enable vector beam pattern measurements to be performed on direct detectors, which have distinct advantages reducing systematic sources of error, allowing beam propagation, and removing the far-field measurement requirement such that complicated optical systems can be measured at a point that is easily accessible, including the near field
An Ultra-Wideband Leaky Lens Antenna for Broadband Spectroscopic Imaging Applications
We present the design, fabrication and characterisation of a broadband leaky
lens antenna for broadband, spectroscopic imaging applications. The antenna is
designed for operation in the 300-900 GHz band. We integrate the antenna
directly into an Al-NbTiN hybrid MKID to measure the beam pattern and absolute
coupling efficiency at three frequency bands centred around 350, 650 and 850
GHz, covering the full antenna band. We find an aperture efficiency over the whole frequency band, limited by lens reflections. We
find a good match with simulations for both the patterns and efficiency,
demonstrating a 1:3 bandwidth in the sub-mm wavelength range for future on-chip
spectrometers.Comment: Accepted for Publication at IEEE Transactions on Antennas and
Propagatio
Conteúdo iônico em um testemunho de firn do Platô Antártico
Este trabalho investiga o conteúdo iônico dos 28,73 m superiores do testemunho BR-IC-2 (88°01'21,3"S; 82°04'21,7"W), coletado durante a travessia antártica chileno-brasileira no verão austral de 2004/05. As concentrações dos Ãons majoritários Na+, K+, Mg2+, Ca2+, Cl-, NO3- e SO42- e do ácido orgânico H3CSO3- (metanosulfonato - MS-) foram determinadas por cromatografia iônica. A datação, baseada na correlação entre as concentrações de Na+ e nssSO42- (sulfato não proveniente de sal marinho), na razão isotópica δD e na identificação de sinais de erupções vulcânicas (Pinatubo / Cerro Hudson em 1993, Agung em 1965 e possivelmente Bristol Island em 1936) constatou uma idade de 85 anos (perÃodo 1918–2003) para o testemunho, com precisão de ± 3 anos. A partir da datação foi possÃvel estabelecer a precipitação anual média nesse sÃtio: 0,15 m eq H2O. Constatou-se uma contribuição de aerossóis de sais marinhos pouco expressiva e uma grande contribuição crustal e biogênica, indicada pelas concentrações de nssCa2+ e nssSO42, respectivamente. O alto valor da razão Cl-/Na+ (4,96) indica que outros fatores, além da contribuição de sal marinho, contribuem para as concentrações desses Ãons, como a entrada ou formação de HCl e a menor depleção do Cl-. As concentrações de K+ e Mg2+, apesar de apresentarem correlação fraca com os outros Ãons, são de origem marinha. O MS- mostra valores pouco expressivos para a região e o NO3- não tem correlação com os outros Ãons, devido à complexidade das fontes, já que este Ãon se apresenta como um aerossol secundário
Ultrafast optical generation of coherent phonons in CdTe1-xSex quantum dots
We report on the impulsive generation of coherent optical phonons in
CdTe0.68Se0.32 nanocrystallites embedded in a glass matrix. Pump probe
experiments using femtosecond laser pulses were performed by tuning the laser
central energy to resonate with the absorption edge of the nanocrystals. We
identify two longitudinal optical phonons, one longitudinal acoustic phonon and
a fourth mode of a mixed longitudinal-transverse nature. The amplitude of the
optical phonons as a function of the laser central energy exhibits a resonance
that is well described by a model based on impulsive stimulated Raman
scattering. The phases of the coherent phonons reveal coupling between
different modes. At low power density excitations, the frequency of the optical
coherent phonons deviates from values obtained from spontaneous Raman
scattering. This behavior is ascribed to the presence of electronic impurity
states which modify the nanocrystal dielectric function and, thereby, the
frequency of the infrared-active phonons
220 fs Er-Yb:glass laser mode-locked by a broadband low-loss Si/Ge saturable absorber
We demonstrate femtosecond performance of an ultra-broadband
high-index-contrast saturable Bragg reflector consisting of a
silicon/silicon-dioxide/germanium structure that is fully compatible with CMOS
processing. This device offers a reflectivity bandwidth of over 700 nm and
sub-picosecond recovery time of the saturable loss. It is used to achieve
mode-locking of an Er-Yb:glass laser centered at 1540 nm, generating 220 fs
pulses, with the broadest output spectrum to date
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