Effects of thermal link in bolometric detectors

The effects of the thermal link on the dynamic behavior of bolometric detectors are discussed. A simple unidimensional model is used to describe the heat diffusion in the link between the sensor and the bath, and the exact general solution is given for the coupled system. Calculations of the dynamic behavior in the time and frequency domains are shown for specific heat sources. A useful approximated formula for the effective heat capacity of the detector is given.     

Signal modelling for TeO2 bolometric detectors

An energetic particle impinging a large mass bolometric detector generates signals of different shape depending on where the energy is deposited: in the absorber or in thethermal sensor. By exploiting this effect and the thermal characteristic of the sensor, all the parameters needed for simulating the dynamic behaviour of the detector for small and large signals were extracted. The model was used for simulating a series of 3 TeO₂ bolometers with mass of 70g and 330g. For an accurate analysis an electric field effect dependance of the electron-phonon thermal conductance and electrons heat capacity in the thermistors used was taken into account. Also an interesting measured and simulated effect was considered regarding the quasi complete thermalized energy given by an -particle.     

The effects of cryocooler microphonics, EMI and temperature variations on bolometric detectors

The use of mechanical coolers for space-based infrared telescopes is becoming a reality with the development of the Planck spacecraft, which will obtain full sky maps of the temperature anisotropy and polarisation of the cosmic microwave background (CMB). The High Frequency Instrument is one of two instruments aboard Planck and will use 48 bolometric detectors operating at 0.1 K. We summarise the performance of the RAL 4 K Joule–Thomson (J–T) system which will precool these detectors, and describe integration aspects of the sensitive bolometric detectors with cryocoolers at system level, in particular the effects of cryocooler vibration, EMI and thermal fluctuations. Full understanding of these systematic sources of noise is critical to enable the microkelvin level scientific signals to be cleanly extracted from the raw data.     

Stability of giant Fabry-Perot cavities of interferometric gravitational-wave detectors

We consider the coupling of the thermoelastic mirror deformations to the resonance of giant cavities involved in interferometric detectors of gravitational waves. As this problem is coupled and nonlinear, instabilities could occur a priori. We analytically solve the coupled problem of thermoelastic deformations and their effect on the laser field, perturbatively, and we show that within the realm of our (physically reasonable) assumptions there are no instabilities that can simulate a false event in the observational frequency range of 1 Hz to 1 kHz.     

Polymer-based nanocomposites for bolometric applications

We have studied the temperature dependences and kinetics of conductivity and the current-voltage characteristics of highly filled polymer-based nanocomposites containing CdS particles with an average size of about 50 Å. The conductivity activation energy, electron density, and electron mobility were determined. The temperature coefficient of resistance of the nanocomposites at room temperature reaches 0.15 K⁻¹. Polymerbased film nanocomposites with semiconductor particles are promising media for highly responsive temperature sensors, in particular, bolometers.     

Modal analysis of astronomical bolometric interferometers

A procedure is described for modeling the behavior of astronomical bolometric interferometers. The scheme is based on the notion of eigenfields. The input and output eigenfields are those field distributions on the sky and at the detector to which the individual telescopes of an interferometer can couple. Eigenfields are more fundamental than eigenmodes and provide, regardless of optical configuration, an orthogonal basis for propagating the second-order statistical properties of a field from a source through the telescopes, through the beam combiners, and onto the detectors. With our scheme, it is possible to calculate the power coupled into coherent, partially coherent, and incoherent imaging arrays and to include the spatially distributed noise sources of the telescopes themselves.     

Stability of the spectral responsivity of cryogenically cooled InSb infrared detectors

The spectral responsivity of two cryogenically cooled InSb detectors was observed to drift slowly with time. The origin of these drifts was investigated and was shown to occur due to a water-ice thin film that was deposited onto the active areas of the cold detectors. The presence of the ice film (which is itself a dielectric film) modifies the transmission characteristics of the antireflection coatings deposited on the active areas of the detectors, thus giving rise to the observed drifts. The magnitude of the drifts was drastically reduced by evacuating the detector dewars while baking them at 50 degrees C for approximately 48 h. All InSb detectors have antireflection coatings to reduce the Fresnel reflections and therefore enhance their spectral responsivity. This work demonstrates that InSb infrared detectors should be evacuated and baked at least annually and in some cases (depending on the quality of the dewar and the measurement uncertainty required) more frequently. These observations are particularly relevant to InSb detectors mounted in dewars that use rubber O rings since the ingress of moisture was found to be particularly serious in this type of dewar.     

Balloon-borne He cryostat for millimetre bolometric photometry

A cryostat including a ³He refrigerator has been designed, built, coupled to a multiband far infrared (FIR) photometer and successfully operated on a balloon flight. Here the cryostat, which is able to cool three bolometers to 0.3 K and one to 1.5 K, is described. The total holding time of the cryostat exceeds 5 days, being limited by exhaustion of the main ⁴He and N₂ baths. The autonomy of the ³He cryostat is more than 50 h, and the recycling time is ≈3 h. The performance of the system in the ARGO 1993 flight is also reported.     

Properties of a silicon surface exposed to nanosecond laser-radiation pulses

Results of the use of nanosecond laser pulses in the technology of production of very-large-scale integration circuits are presented. It is shown that, depending on the conditions of processing of silicon by these pulses, they can avoid mechanical failure of the silicon crystal lattice and form a gettering layer that cleans the silicon from impurities. __________ Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 81, No. 3, pp. 592–595, May–June, 2008.     

Absorption of laser-radiation energy by femtosecond laser spark in air

The fraction of focused femtosecond laser radiation energy absorbed by a laser-induced spark in air has been studied. It is established that the absorbed energy exhibits nonlinear growth with increasing energy of the laser pulse. The threshold power for laser-induced spark formation in air is 5.2 GW.