A. De Michele

'Galileo Galilei' (GG): space test of the weak equivalence principle to 10^(−17) and laboratory demonstrations

The small satellite ‘Galileo Galilei’ (GG) will test the universality of free fall and hence the weak equivalence principle which is the founding pillar of general relativity to 1 part in 10 17 . It will use proof masses whose atoms differ substantially from one another in their mass energy content, so as to maximize the chance of violation. GG will improve by four orders of magnitude the current best ‘E¨ ot-Wash’ tests based on slowly rotating torsion balances, which have been able to reach their thermal noise level. In GG, the expected violation signal is a relative displacement between the proof masses of � 0.6 pm caused by a differential acceleration aGG � 8 × 10 −17 ms −2 pointing to the center of mass of the Earth as the satellite orbits around it at νGG � 1.7 × 10 −4 Hz. GG will fly an innovative acceleration sensor based on rapidly rotating macroscopic test masses weakly coupled in 2D which up-converts the signal to νspin � 1H z, a value well above the frequency of natural oscillations of the masses relative to each other νd = 1/Td � 1/(540 s). The sensor is unique in that it ensures high rotation frequency, low thermal noise and no attenuation of the signal strength (Pegna et al 2011 Phys. Rev. Lett. 107 200801). A readout based on a very

A new pulsed CO2 laser yielding new FIR laser lines from CH3OD pumped by the 10P and 10HP lines

Using a novel CO2 pulsed laser that presents high peak power (several hundreds of watts) together with high spectral purity, we have reinvestigated the CH3OD isotopomer of methanol as a source of far infrared laser emissions pumped by the 10P and 10HP CO2 laser lines. Thirty-five new lines have been observed and characterized for wavelength, offset, relative polarization, optimum operation pressure and relative intensity.

New FIR Laser Lines from CHD2OH Methanol

We have investigated CHD2OH methanol as source of far-infrared (FIR) laser radiation using the optical pumping technique. Our new waveguide pulsed CO2 laser, with peak powers as high as some kW, has allowed us to observe 12 new lines. Each of them is characterized in wavelength, relative polarization, intensity, optimum operating pressure and pump offset from the center of the exciting CO2 line.

Frequency Characterization of a Terahertz Quantum-Cascade Laser

In this paper, the frequency characteristics of a terahertz quantum-cascade laser (QCL) operating around 2.5-THz in the pulsed regime have been studied by means of a heterodyne detection by using an optically pumped molecular laser as the local oscillator. The absolute frequency of the QCL can be determined with an accuracy of 1 MHz due to the pulse-to-pulse jitter of the QCL. The frequency tunability as a function of the injection current of the QCL is estimated to be around +2 GHz/A

Coherent multiwave heterodyne frequency measurement of a far-infared laser by means of a femtosecond laser comb

We demonstrate the possibility of using a femtosecond laser to measure with high accuracy the frequency of a far-infrared (FIR) monochromatic source, such as an optically pumped molecular laser, by generating in a suitable mixer a signal in the radio-frequency region at the frequency difference between n steps of a femtosecond comb and the FIR source. All the couples of modes lying a distance of n steps from one another contribute coherently to the heterodyne signal. The technique has been tested up to 670 GHz.

GaSb and InAs: New Materials for Metal-Semiconductor Point-Contact Diodes

Metal-semiconductor point contact diodes have proved to be good detectors and mixers for radiation from the far-infrared to visible. Until now GaAs, InSb and InP are the most studied and used semiconductor materials for these devices. In this work we present the performance in the visible and infrared region for metal-semiconductor point-contact diodes with GaSb or InAs as the semiconductor layers. These two new materials have shown good characteristics.

Measurements of near infrared frequency mixing by metal-semiconductor point-contact diodes

We tested the performance of metal-semiconductor point-contact diodes as mixers in the near infrared region. We performed preliminary experiments in order to phase-lock two diode laser at 850 nm some hundred GHz apart. We used GaSb, InAs and InSb as semiconductor layer. The frequency bridge between the two lasers was covered by a Gunn diode frequency locked to a 1 GHz oscillator.

Heterodyne measurements in FIR range with a femtosecond laser used as a reference oscillator

An heterodyne technique employing ultra-wide band Schottky diodes and a femtosecond pulsed laser was tested to perform frequency measurements in the far infrared range. Preliminary experiments demonstrate an efficient frequency down-conversion in Schottky diodes by mixing the microwave radiation with the output of a femtosecond laser used as a reference local oscillator.

FIR laser lines from CH3OD: A review

The methanol isotopic species CH3OD has also proved to be an efficient and powerful medium to generate radiation in the far infrared (FIR) region. After the critical review of 1994, six papers have been published dealing with new FIR laser lines from this molecule. As a consequence of the use of wide tunability waveguide CO2 lasers as well as a new pulsed CO2 laser operating at hot and sequential bands, as of optical pumping sources, the total number of the FIR laser lines increased from 122 in 1994 to 227 today. In this communication we present an updated and complete catalogue of FIR laser lines generated from CH3OD. Information on wavelength, offset, relative polarization, intensity, and optimum operation pressure is generally available.