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 $\sim-30$ 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 $\sim-35$ 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

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

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

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

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

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

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

Obstacles and opportunities in the functionalanalysis of extracellular vesicle RNA – an ISEVposition paper

The release of RNA-containing extracellular vesicles (EV) into the extracellular milieu has been demonstrated in a multitude of different in vitro cell systems and in a variety of body fluids. RNA-containing EV are in the limelight for their capacity to communicate genetically encoded messages to other cells, their suitability as candidate biomarkers for diseases, and their use as therapeutic agents. Although EV-RNA has attracted enormous interest from basic researchers, clinicians, and industry, we currently have limited knowledge on which mechanisms drive and regulate RNA incorporation into EV and on how RNA-encoded messages affect signalling processes in EV-targeted cells. Moreover, EV-RNA research faces various technical challenges, such as standardisation of EV isolation methods, optimisation of methodologies to isolate and characterise minute quantities of RNA found in EV, and development of approaches to demonstrate functional transfer of EV-RNA in vivo. These topics were discussed at the 2015 EV-RNA workshop of the International Society for Extracellular Vesicles. This position paper was written by the participants of the workshop not only to give an overview of the current state of knowledge in the field, but also to clarify that our incomplete knowledge – of the nature of EV(-RNA)s and of how to effectively and reliably study them – currently prohibits the implementation of gold standards in EV-RNA research. In addition, this paper creates awareness of possibilities and limitations of currently used strategies to investigate EV-RNA and calls for caution in interpretation of the obtained data