P. L. Richards

THE MULTIBAND IMAGING PHOTOMETER FOR SPITZER (MIPS)

The Multiband Imaging Photometer for Spitzer (MIPS) provides long-wavelength capability for the mission in imaging bands at 24, 70, and 160 ?m and measurements of spectral energy distributions between 52 and 100 ?m at a spectral resolution of about 7%. By using true detector arrays in each band, it provides both critical sampling of the Spitzer point-spread function and relatively large imaging fields of view, allowing for substantial advances in sensitivity, angular resolution, and efficiency of areal coverage compared with previous space far-infrared capabilities. The 24 ?m array has excellent photometric properties, and measurements with rms relative errors of about 1% can be obtained. The two longer-wavelength arrays use detectors with poor photometric stability, but a system of onboard stimulators used for relative calibration, combined with a unique data pipeline, produce good photometry with rms relative errors of less than 10%.

MAXIMA-1: A Measurement of the Cosmic Microwave Background Anisotropy on Angular Scales of 10'-5°

We present a map and an angular power spectrum of the anisotropy of the cosmic microwave background (CMB) from the first flight of MAXIMA. MAXIMA is a balloon-borne experiment with an array of 16 bolometric photometers operated at 100 mK. MAXIMA observed a 124 square degrees region of the sky with 10 arcminute resolution at frequencies of 150, 240 and 410 GHz. The data were calibrated using in-flight measurements of the CMB dipole anisotropy. A map of the CMB anisotropy was produced from three 150 and one 240 GHz photometer without need for foreground subtractions. Analysis of this CMB map yields a power spectrum for the CMB anisotropy over the range 36 < l < 785. The spectrum shows a peak with an amplitude of 78 +/- 6 micro-Kelvin at l ~ 220 and an amplitude varying between ~40 micro-Kelvin and ~50 micro-Kelvin for 400 < l < 785.

Bolometers for infrared and millimeter waves

This review describes bolometric detectors for infrared and millimeter waves. The introduction sketches the history of modern bolometers, indicates how they fit into the more general class of thermal detectors, and describes the types of applications for which they are the optimum solution. Section I is a tutorial introduction to the elementary theories of bolometer response, of thermal radiation, and of bolometer noise. Important results are derived from the laws of thermal physics in the simplest possible way. The more rigorous theories of bolometer response and noise that are required for quantitative understanding and optimization are then summarized. This material is intended to provide the background required by workers who wish to choose the appropriate bolometer technology for a given measurement, or to evaluate a novel technology. Section II, then describes the various components of an efficient bolometer and gives details of the fabrication and performance of modern bolometers. This discussion f...

Cosmology from MAXIMA-1, BOOMERANG, and COBE DMR Cosmic Microwave Background Observations

Recent results from BOOMERANG-98 and MAXIMA-1, taken together with COBE DMR, provide consistent and high signal-to-noise measurements of the cosmic microwave background power spectrum at spherical harmonic multipole bands over 2<l less similar to 800. Analysis of the combined data yields 68% (95%) confidence limits on the total density, Omega(tot) approximately 1.11+/-0.07 (+0.13)(-0.12), the baryon density, Omega(b)h(2) approximately 0.032(+0.005)(-0.004) (+0.009)(-0.008), and the scalar spectral tilt, n(s) approximately 1.01(+0.09)(-0.07) (+0.17)(-0.14). These data are consistent with inflationary initial conditions for structure formation. Taken together with other cosmological observations, they imply the existence of both nonbaryonic dark matter and dark energy in the Universe.

Constraints on Cosmological Parameters from MAXIMA-1

We set new constraints on a seven-dimensional space of cosmological parameters within the class of inflationary adiabatic models. We use the angular power spectrum of the cosmic microwave background measured over a wide range of l in the first flight of the MAXIMA balloon-borne experiment (MAXIMA-1) and the low-l results from the COBE Differential Microwave Radiometer experiment. We find constraints on the total energy density of the universe, Ω = 1.0img1.gif, the physical density of baryons, Ωbh2 = 0.03 ± 0.01, the physical density of cold dark matter, Ωcdmh2 = 0.2img2.gif, and the spectral index of primordial scalar fluctuations, ns = 1.08 ± 0.1, all at the 95% confidence level. By combining our results with measurements of high-redshift supernovae we constrain the value of the cosmological constant and the fractional amount of pressureless matter in the universe to 0.45 < ΩΛ < 0.75 and 0.25 < Ωm < 0.50, at the 95% confidence level. Our results are consistent with a flat universe and the shape parameter deduced from large-scale structure, and in marginal agreement with the baryon density from big bang nucleosynthesis.

Superconducting detectors and mixers for millimeter and submillimeter astrophysics

Superconducting detectors will play an increasingly significant role in astrophysics, especially at millimeter through far-IR wavelengths, where the scientific opportunities include key problems in astronomy and cosmology. Superconducting detectors offer many benefits: outstanding sensitivity, lithographic fabrication, and large array sizes, especially through the recent development of multiplexing techniques. This paper describes the scientific opportunities, the basic physics of these devices, the techniques for radiation coupling, and reviews the recent progress in direct detectors, such as transition-edge bolometers, and the work on tunnel junction (superconductor-insulator-superconductor) and hot-electron mixers.

The 24 Micron Source Counts in Deep Spitzer Space Telescope Surveys

Galaxy source counts in the infrared provide strong constraints on the evolution of the bolometric energy output from distant galaxy populations. We present the results from deep 24 μm imaging from Spitzer surveys, which include ≈5 × 10^4 sources to an 80% completeness of ≃ 60 μJy. The 24 μm counts rapidly rise at near-Euclidean rates down to 5 mJy, increase with a super-Euclidean rate between 0.4 and 4 mJy, and converge below ~0.3 mJy. The 24 μm counts exceed expectations from nonevolving models by a factor of ≳10 at S_ν ~ 0.1 mJy. The peak in the differential number counts corresponds to a population of faint sources that is not expected from predictions based on 15 μm counts from the Infrared Space Observatory. We argue that this implies the existence of a previously undetected population of infrared-luminous galaxies at z ~ 1-3. Integrating the counts to 60 μJy, we derive a lower limit on the 24 μm background intensity of 1.9 ± 0.6 nW m^(-2) sr^(-1) of which the majority (~60%) stems from sources fainter than 0.4 mJy. Extrapolating to fainter flux densities, sources below 60 μJy contribute 0.8^(+0.9)_(-0.4) nW m^(-2) sr^(-1) to the background, which provides an estimate of the total 24 μm background of 2.7^(+1.1)_(-0.7) nW m^(-2) sr^(-1).

Generation of Far‐Infrared Radiation by Picosecond Light Pulses in LiNbO3

We have observed far‐infrared radiation generated by picosecond pulses in LiNbO3 with several different phase‐matching conditions. The output spectra, analyzed by a far‐infrared Michelson interferometer and by a Fabry‐Perot interferometer, agree well with theoretical calculations. The laser pulsewidth deduced from these measurements was about 2 psec in comparison with 5 psec obtained from two‐photon fluorescence measurements.

Quasiparticle heterodyne mixing in SIS tunnel junctions

The rapid onset of quasiparitcle tunneling current in superconductor‐insulator‐superconductor (Josephson) junctions at voltages above 2Δ/e is being used for millimeter‐wave heterodyne mixing. Junctions with a 2‐μm diameter and RN=50 Ω have little capacitive shunting at the signal frequency of 36 GHz. Because there is no series resistance, residual capacitance can be tuned out. Double sideband conversion efficiencies of 0.32 and mixer noise temperatures as low as TM⩽7 K=4hν/k have been observed. The results are compared with shot‐noise‐limited mixer theory. Photon‐assisted tunneling effects are seen which indicate the approach to photon‐noise‐limited operation.

Superconductive bolometers for submillimeter wavelengths

Three types of composite superconductive bolometers are described in which the temperature‐sensitive element is a superconducting film at the transition temperature, a superconductor–normal metal–superconductor Josephson junction, or a superconductor–insulator–normal metal quasiparticle tunneling junction. The temperature‐sensitive element is evaporated onto a sapphire substrate on the reverse side of which is a bismuth film to absorb the submillimeter radiation. The noise limitations of each type of bolometer are calculated. The fabrication and measured performance of the transition‐edge bolometer and the Josephson‐junction bolometer are described. The best electrical (noise‐equivalent power) NEP obtained with a transition‐edge bolometer fabricated on a 4×4×0.005‐mm sapphire substrate is (1.7±0.1) ×10−15 W Hz−1/2 at 2 Hz at an operating temperature of 1.27 K. This NEP is within a factor of 2 of the thermal noise limit. The effective absorptivity of the bismuth film is measured to be 0.47±0.05, and the co...