A tunable clamshell cavity for wavelike dark matter searches.

Here, we present a frequency tuning mechanism for microwave cavities designed for axion dark matter searches and show that it provides a range of at least 200 MHz for the fundamental mode TM010 resonant at ∼10 GHz. The apparatus is based on a clamshell cavity, with the two semi-cells held together at a fixed joint while the other side opens to tune the frequency of the resonant modes. Measurements of the cavity frequencies and quality factor were taken at liquid helium temperature as the aperture was increased incrementally to ∼2°. We show that the frequency shift is approximately linear with respect to the angle of aperture with no mode crossings present for an aperture less than 2°. Furthermore, the form factor and quality factor of the TM010 mode remain relatively constant throughout the tuning as predicted by simulation.

High quality factor photonic cavity for dark matter axion searches.

Searches for dark matter axions involve the use of microwave resonant cavities operating in a strong magnetic field. Detector sensitivity is directly related to the cavity quality factor, which is limited, until recently, to the use of non-superconducting metals by the presence of the external magnetic field. In this paper, we present a cavity of novel design whose quality factor is not affected by a magnetic field. It is based on a photonic structure by the use of sapphire rods. The quality factor at cryogenic temperature is in excess of 5 × 105 for a selected mode.

Axion Search with a Quantum-Limited Ferromagnetic Haloscope.

A ferromagnetic axion haloscope searches for dark matter in the form of axions by exploiting their interaction with electronic spins. It is composed of an axion-to-electromagnetic field transducer coupled to a sensitive rf detector. The former is a photon-magnon hybrid system, and the latter is based on a quantum-limited Josephson parametric amplifier. The hybrid system consists of ten 2.1 mm diameter yttrium iron garnet spheres coupled to a single microwave cavity mode by means of a static magnetic field. Our setup is the most sensitive rf spin magnetometer ever realized. The minimum detectable field is 5.5×10^{-19} T with 9 h integration time, corresponding to a limit on the axion-electron coupling constant g_{aee}≤1.7×10^{-11} at 95% C.L. The scientific run of our haloscope resulted in the best limit on dark matter axions to electron coupling constant in a frequency span of about 120 MHz, corresponding to the axion-mass range 42.4-43.1 µeV. This is also the first apparatus to perform a wide axion-mass scanning by only changing the static magnetic field.

Experimental setup for the growth of solid crystals of inert gases for particle detection.

Low energy threshold detectors are necessary in many frontier fields of the experimental physics. In this work, we present a novel detection approach based on pure or doped matrices of inert gases solidified at cryogenic temperatures. The small energy release of the incident particle can be transferred directly (in pure crystals) or through a laser-driven ionization (in doped materials) to the electrons of the medium that are then converted into free electrons. The charge collection process of the electrons that consists in their drift within the crystal and their extraction through the solid-vacuum interface gives rise to an electric signal that we exploit for preliminary tests of charge collection and crystal quality. Such tests are carried out in different matrices of neon and methane using an UV-assisted apparatus for electron injection in crystals.

Optical Manipulation of a Magnon-Photon Hybrid System.

We demonstrate an all-optical method for manipulating the magnetization in a 1-mm yttrium-iron-garnet (YIG) sphere placed in a ∼0.17 T uniform magnetic field. A harmonic of the frequency comb delivered by a multi-GHz infrared laser source is tuned to the Larmor frequency of the YIG sphere to drive magnetization oscillations, which in turn give rise to a radiation field used to thoroughly investigate the phenomenon. The radiation damping issue that occurs at high frequency and in the presence of highly magnetizated materials has been overcome by exploiting the magnon-photon strong coupling regime in microwave cavities. Our findings demonstrate an effective technique for ultrafast control of the magnetization vector in optomagnetic materials via polarization rotation and intensity modulation of an incident laser beam. We eventually get a second-order susceptibility value of ∼10^{-7} cm^{2}/MW for single crystal YIG.

A contactless microwave-based diagnostic tool for high repetition rate laser systems.

We report on a novel electro-optic device for the diagnostics of high repetition rate laser systems. It is composed of a microwave receiver and of a second order nonlinear crystal, whose irradiation with a train of short laser pulses produces a time-dependent polarization in the crystal itself as a consequence of optical rectification. This process gives rise to the emission of microwave radiation that is detected by a receiver and is analyzed to infer the repetition rate and intensity of the pulses. We believe that this new method may overcome some of the limitations of photodetection techniques.

Generation of microwave radiation by nonlinear interaction of a high-power, high-repetition rate, 1064 nm laser in KTiOPO4 crystals.

We report measurements of microwave (RF) generation in the centimeter band accomplished by irradiating a nonlinear KTiOPO4 crystal with a home-made, infrared laser at 1064 nm as a result of optical rectification. The laser delivers pulse trains of duration up to 1 µs. Each train consists of several high-intensity pulses at an adjustable repetition rate of approximately 4.6 GHz. The duration of the generated RF pulses is determined by that of the pulse trains. We have investigated both microwave- and second harmonic generation as a function of the laser intensity and of the orientation of the laser polarization with respect to the crystallographic axes of KTP.

A laser system for the parametric amplification of electromagnetic fields in a microwave cavity.

We describe recent improvements in the development of the high power laser system used in the motion induced radiation (MIR) experiment to amplify electromagnetic fields inside a microwave cavity. The improvements made on the oscillator stabilization, the pulse train shaping device, and the spatial beam uniformity are reported.