44 research outputs found
Investigation of the Effects of the Multiplication Area Shape on the Operational Parameters of InGaAs/InAlAs SPADs
A 2D model of an InGaAs/InAlAs single photon avalanche photodiode has been
developed. The influence of the active area structure in the multiplication
region on the diode's operating parameters has been studied. It was found that
changing the diameter of the structure's active region leads to a change in the
dark current in the linear part of the current-voltage curve and a change in
the breakdown voltage. Reducing the diameter of the active region from 25
m to 10 m allowed decreasing the dark current in the linear mode by
about dB. It has been shown that the quality of the SPAD device can be
assessed by knowing the avalanche breakdown voltage and the overall
current-voltage curve plot if we consider structures with the same
multiplication region thickness and different remaining layers. The higher the
breakdown voltage, the better the structure's quality due to smaller local
increases in the field strength. Following this statement, we conclude that for
further use in single-photon detectors, it is reasonable to pick specific SPADs
from a batch on the sole basis of their current-voltage curves
Dead time duration and active reset influence on the afterpulse probability of InGaAs/InP SPAD based SPDs
We perform the detailed study of the afterpulse probability's dependence in
the InGaAs/InP sine-gated SPAD on the dead time and the used approach for its
implementation. We have found that the comparator's simple latching can
significantly reduce afterpulses' probability, even without using a dead time
pulse that lowers the diode bias voltage. We have found that with a low
probability of afterpulse ( 10 mus), it
is sufficient to use a circuit with latching of the comparator, which will
significantly simplify the development of an SPD device for applications in
which such parameters are acceptable. We also proposed a precise method for
measuring and the afterpulse and presented a model describing the recurrent
nature of this effect. We have shown that it should not use a simple model to
describe the afterpulse probability due to rough underlying physical processes.
A second-order model is preferable
Millimetre-wave range optical properties of BIBO
We present the thorough studies of optical properties of BiB3O6 (BIBO) crystal in the millimeter-wave (subterahertz) range. We observe a large birefringence Δn = nZ −nX = 1.5 and the values of absorption coefficients of all three axes to be less than 0.5 cm−1 at the frequency of 0.3 THz. The difference from visible range in angle ϕ between the dielectric axis z and crystallophysical axis X is found to be more than 6°. The simulated phase-matching curves in the xz plane of the crystal show the optimal value of the angle θ to be around 25.5°±1° for an efficient millimeter-wave generation under the pump of 1064 nm laser radiation
The dielectric tensor rotation angle and optical properties of a nonlinear crystal of bismuth triborate in the millimeter wave range
Passive Microwave Radiometry and microRNA Detection for Breast Cancer Diagnostics
Breast cancer prevention is an important health issue for women worldwide. In this study, we compared the conventional breast cancer screening exams of mammography and ultrasound with the novel approaches of passive microwave radiometry (MWR) and microRNA (miRNA) analysis. While mammography screening dynamics could be completed in 3–6 months, MWR provided a prediction in a matter of weeks or even days. Moreover, MWR has the potential of being complemented with miRNA diagnostics to further improve its predictive quality. These novel techniques can be used alone or in conjunction with more established techniques to improve early breast cancer diagnosis
Passive Microwave Radiometry for the Diagnosis of Coronavirus Disease 2019 Lung Complications in Kyrgyzstan
The global spread of severe acute respiratory syndrome coronavirus 2, which causes coronavirus disease 2019 (COVID-19), could be due to limited access to diagnostic tests and equipment. Currently, most diagnoses use the reverse transcription polymerase chain reaction (RT-PCR) and chest computed tomography (CT). However, challenges exist with CT use due to infection control, lack of CT availability in low- and middle-income countries, and low RT-PCR sensitivity. Passive microwave radiometry (MWR), a cheap, non-radioactive, and portable technology, has been used for cancer and other diseases’ diagnoses. Here, we tested MWR use first time for the early diagnosis of pulmonary COVID-19 complications in a cross-sectional controlled trial in order to evaluate MWR use in hospitalized patients with COVID-19 pneumonia and healthy individuals. We measured the skin and internal temperature using 30 points identified on the body, for both lungs. Pneumonia and lung damage were diagnosed by both CT scan and doctors’ diagnoses (pneumonia+/pneumonia−). COVID-19 was determined by RT-PCR (covid+/covid−). The best MWR results were obtained for the pneumonia−/covid− and pneumonia+/covid+ groups. The study suggests that MWR could be used for diagnosing pneumonia in COVID-19 patients. Since MWR is inexpensive, its use will ease the financial burden for both patients and countries. Clinical Trial Number: NCT04568525
Potential of sub-THz-wave generation in Li2B4O7 nonlinear crystal at room and cryogenic temperatures
Due to their high optical damage threshold, borate crystals can be used for the efficient nonlinear down-conversion of terawatt laser radiation into the terahertz (THz) frequency range of the electromagnetic spectrum. In this work, we carried out a thorough study of the terahertz optical properties of the lithium tetraborate crystal (Li2B4O7; LB4) at 295 and 77 K. Approximating the terahertz refractive index in the form of Sellmeier’s equations, we assessed the possibility of converting the radiation of widespread high-power laser sources with wavelengths of 1064 and 800 nm, as well as their second and third harmonics, into the THz range. It was found that four out of eight types of three-wave mixing processes are possible. The conditions for collinear phase matching were fulfilled only for the o - e -o type of interaction, while cooling the crystal to 77 K did not practically affect the phase-matching curves. However, a noticeable increase of birefringence in the THz range with cooling (from 0.12 to 0.16) led to an increase in the coherence length for o-o-e and e-e-e types of interaction, which are potentially attractive for the down-conversion of ultrashort laser pulses