Interband Cascade Lasers (ICLs) are gaining field in molecular sensing thanks to their compact sizes and low-power consumption. They emit in the 3-6 μm range, and are valid alternative to QCLs especially for on-field measurement. Their suitability for high-resolution spectroscopy and metrology critically depends on their frequency stability and linewidth.
Here we investigate this issues, reporting experimental studies of the frequency noise and intrinsic linewidth of an ICL at 4.6 μm. The main differences with respect to other semiconductor lasers are discussed, as well as quantum-limited operation achievable using low-noise current drivers and frequency locking to high-performance optical resonators.
Thanks to their compactness and low-power consumption, Interband Cascade Lasers (ICLs) are emerging sources for mid-infrared (MIR) molecular sensing below 6 µm. Understanding their noise features is of fundamental importance for applications like high-sensitivity and high-resolution spectroscopy. It could unveil details of their intrinsic physical behavior and, similarly to what happened for Quantum Cascade Lasers (QCLs), lead to the development of frequency and phase stabilization techniques for linewidth reduction. In this manuscript, we discuss the importance of full frequency noise characterization for ICLs, pointing out the main similarities and differences with respect to QCLs, and we show preliminary noise measurements. The frequency noise spectrum is analyzed and discussed, and the laser linewidth over different timescales calculated.
Interband and Quantum Cascade Lasers are key sources for MIR molecular sensing. Understanding their noise features and stabilizing their emission is of fundamental importance for applications like precision spectroscopy and metrology. High-Q crystalline Whispering Gallery Mode Resonators have proven to be powerful tools for characterization and stabilization of lasers from the UV to the MIR. Here, we report our recent results on Whispering Gallery Mode Resonators used for frequency characterization, stabilization and linewidth narrowing of Interband and Quantum Cascade Lasers. These results pave the way to new classes of compact MIR sources usable in Space missions, Metrology and Fundamental Physics.
The aim of this work is to describe the latest results of new technological concepts for Large Aperture Telescopes Technology (LATT) using thin deployable lightweight active mirrors. This technology is developed under the European Space Agency (ESA) Technology Research Program and can be exploited in all the applications based on the use of primary mirrors of space telescopes with large aperture, segmented lightweight telescopes with wide Field of View (FOV) and low f/#, and LIDAR telescopes. The reference mission application is a potential future ESA mission, related to a space borne DIAL (Differential Absorption Lidar) instrument operating around 935.5 nm with the goal to measure water vapor profiles in atmosphere. An Optical BreadBoard (OBB) for LATT has been designed for investigating and testing two critical aspects of the technology:
1) control accuracy in the mirror surface shaping. 2) mirror survivability to launch.
The aim is to evaluate the effective performances of the long stroke smart-actuators used for the mirror control and to demonstrate the effectiveness and the reliability of the electrostatic locking (EL) system to restraint the thin shell on the mirror backup structure during launch. The paper presents a comprehensive vision of the breadboard focusing on how the requirements have driven the design of the whole system and of the various subsystems. The manufacturing process of the thin shell is also presented.
The increasing interest on space telescopes for scientific applications leads to implement the manufacturing technology of the most critical element, i.e. the primary mirror: being more suitable a large aperture, it must be lightweight and deployable. The presented topic was originally addressed to a spaceborne DIAL (Differential Absorption LIDAR) mission operating at 935.5 nm for the measurement of water vapour profile in atmosphere, whose results were presented at ICSO 2006 and 2008.
Aim of this paper is to present the latest developments on the main issues related to the fabrication of a breadboard, covering two project critical areas identified during the preliminary studies: the design and performances of the long-stroke actuators used to implement the mirror active control and the mirror survivability to launch via Electrostatic Locking (EL) between mirror and backplane. The described work is developed under the ESA/ESTEC contract No. 22321/09/NL/RA.
The lightweight mirror is structured as a central sector surrounded by petals, all of them actively controlled to reach the specified shape after initial deployment and then maintained within specs for the entire mission duration. The presented study concerns: a) testing the Carbon Fiber Reinforced Plastic (CFRP) backplane manufacturing and EL techniques, with production of suitable specimens; b) actuator design optimisation; c) design of the deployment mechanism including a high precision latch; d) the fabrication of thin mirrors mock-ups to validate the fabrication procedure for the large shells.
The current activity aims to the construction of an optical breadboard capable of demonstrating the achievement of all these coupled critical aspects: optical quality of the thin shell mirror surface, actuators performances and back-plane - EL subsystem functionality.
The concept of a low areal density primary mirror, actively controlled by actuators, has been investigated through a demonstration prototype. A spherical mirror (400 mm diameter, 2.7 Kg mass) has been manufactured and tested in laboratory and on the optical bench, to verify performance, controllability and optical quality. In the present paper we will describe the prototype and the test results.
The LATT project is an ESA contract under TRP programme to demonstrate the scalability of the technology from ground-based adaptive mirrors to space active primary mirrors. A prototype spherical mirror based on a 40 cm diameter 1 mm thin glass shell with 19 contactless, voice-coil actuators and co-located position sensors have been manufactured and integrated into a final unit with an areal density lower than 20 kg/m2. Laboratory tests demonstrated the controllability with very low power budget and the survival of the fragile glass shell exposed to launch accelerations, thanks to an electrostatic locking mechanism; such achievements pushes the technology readiness level toward 5. With this prototype, the LATT project explored the feasibility of using an active and lightweight primary for space telescopes. The concept is attractive for large segmented telescopes, with surface active control to shape and co-phase them once in flight. In this paper we will describe the findings of the technological advances and the results of the environmental and optical tests.
The Large Aperture Telescope Technology (LATT) goes beyond the current paradigm of future space telescopes, based on a deformable mirror in the pupil relay. Through the LATT project we demonstrated the concept of a low-weight active primary mirror, whose working principle and control strategy benefit from two decades of advances in adaptive optics for ground-based telescopes. We developed a forty centimeter spherical mirror prototype, with an areal density lower than 17 kg/m2, controlled through contactless voice coil actuators with co-located capacitive position sensors. The prototype was subjected to thermo-vacuum, vibration and optical tests, to push its technical readiness toward level 5. In this paper we present the background and the outcomes of the LATT activities under ESA contract (TRP programme), exploring the concept of a lightweight active primary mirror for space telescopes. Active primaries will open the way to very large segmented apertures, actively shaped, which can be lightweight, deployable and accurately phased once in flight.
Infrared (IR) digital holography (DH) based on CO2 lasers has proven to be a powerful coherent imaging technique due
to the reduced sensitivity to mechanical vibrations, to the increased field of view, to the high optical power and to
possible vision through scattering media, such as smoke. In this contribution we report IR DH based on the combination
of quantum cascade laser (QCL) sources and a high resolution microbolometric camera. QCLs combine highly desirable
features for coherent imaging, such as compactness, high optical power, and spectral purity. The present availability of
external cavity mounted QCLs having a broad tuning range, makes them suitable sources for multiple wavelength
holographic interferometry. In addition, QCL emission covers several windows throughout a large portion of the IR
spectrum, from the mid-IR to the terahertz region. This allows taking advantage of the different optical response of the
imaged objects at different frequencies, which is crucial for applications such as non-destructive testing and biomedical
imaging. Our holographic system is suitable for the acquisition of both transmission holograms of transparent objects
and speckle holograms of scattering objects, which can be processed in real time to retrieve both amplitude and phase.
We report on three different quartz enhanced photoacoustic (QEPAS) sensors operating in the near-IR, mid-IR and THz
spectral ranges, employing quartz tuning forks of different sizes and shapes. To test our sensors in the near-IR we used a
diode laser working at 2.7 μm, while in the mid-IR we employed a quantum cascade laser (QCL) operating at 7.9 μm,
fiber-coupled to the QEPAS cell. In the THz range we employed a QCL emitting at 2.95 THz. H2S absorption features
with line-strength up to 10-20 cm/mol were selected and QEPAS normalized noise-equivalent absorption in the 10-10
W•cm-1•Hz-1/2 range was achieved..
GIANO is an high resolution cross-dispersed spectrometer operating at near IR wavelengths (0.9-2.5 microns) which will
be soon commissioned at the 3.6m TNG Italian telescope in La Palma. One of its most ambitious aims is searching for
earth-like planets with habitable conditions around very cool main sequence stars. This requires measurements of radial
velocities with accuracies of a few m/s which can be achieved by means of a gas absorption cell containing a mixture of
the halogen-hydrates HCl, HBr and HI. We present here the results of the laboratory work for the construction and
characterization of such cell.
GIANO is an high resolution cross-dispersed spectrometer operating at near IR wavelengths (0.9-2.5 microns). One of its primary aims is to measure radial velocities of cool stars with an accuracy of a few m/sec. To this purpose, the spectrometer requires a gas absorption cell which should ideally produce several hundreds of measurable lines distributed over the whole wavelengths range. We show that this can be conveniently achieved using a combination of halogen hydrates, namely HCl, HBr and HI. We present and discuss the design and development of such a cell.
GIANO is an infrared (0.9-2.5 μm cross-dispersed echelle spectrometer designed to achieve high resolution, high throughput, wide band coverage and very high stability for accurate radial velocity measurements. It also includes polarimetric capabilities and a low resolution mode with RS ~ 400 and complete 0.75-2.5 μm coverage. This makes it a very versatile, common user instrument which will be permanently mounted and available on the Nasmyth-B foci of the Telescopio Nazionale Galileo (TNG) located at Roque de Los Muchachos Observatory (ORM), La Palma, Spain. The project is fast-track and relies on well known, relatively standard technologies. It has been recognized as one of the top priority instrumental projects of INAF (the Italian National Institute of Astronomy) and received its first financing for the phase-A study in October 2003. Integration in the laboratory is planned to start before the end of 2006, commissioning at the telescope is foreseen within 2007 and scientific operations in 2008. One of the most important scientific goals is the search for rocky planets with habitable conditions around low-mass stars. If completed on time, GIANO will be the first and only IR instrument operating worldwide
providing the combination of efficiency, spectral resolution, wavelength coverage and stability necessary for this type of research. With its unique combination of high and low resolution modes, GIANO will also be a very flexible common-user instrument ideal e.g. for quantitative spectroscopy of brown dwarfs, stars and stellar clusters as well as for the determination of the spectral energy distribution of faint/red objects such as high redshift galaxies. The expected limiting magnitudes are such that GIANO will be able to deliver good quality HR spectra of any 2MASS object and LR spectra of any object detected in the UKIDSS large area survey.
GIANO is an infrared (0.9-2.5 μm) cross-dispersed echelle spectrometer designed to achieve high throughput, high resolving power, wide band coverage and high accuracy radial velocity measurements. It also includes polarimetric capabilities and a low resolution mode that make it a very versatile, common user instrument which will be permanently mounted and available at one of the Nasmyth foci of the Telescopio Nazionale Galileo (TNG) located at Roque de Los Muchachos Observatory (ORM), La Palma, Spain. GIANO was selected by INAF as the top priority instrument among those proposed within the Second Generation Instrumentation Plan of the TNG. More information on this project can be found at the web page http://www.bo.astro.it/giano
An instrument which will measure the atmospheric concentration of carbon dioxide with a resolution of one part in 104 will be realized in the frame of 'environment and climate' program of the European Community. The aims are the evaluation of global climate changes and the measurement of the flux at the interface air-sea. The requirements for such an instrument apart form resolution are stability and insensitivity to water. This instrument is based on room temperature tunable diode lasers at about 6350 cm(superscript - by laser sources with the required spectral characteristics. The atmospheric concentration of carbon dioxide is about 350 ppm and its absorbance along a path of 100 m is of the order of 1 percent. The measurement will be performed in a multipass cell. A second cell will supply the references for frequency stabilization and laser power monitoring. The detection is realized through frequency modulation techniques. The various aspects of the work presently in progress will be presented: spectroscopy, optical layout, detection method and so on.
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