Nicola Coluccelli

Coluccelli Nicola received the degree in Telecommunications Engineering with honors, from the Polytechnic of Milan in 2004, and the PhD in Physics at the PhD School of the Polytechnic of Milan in 2008. He later obtained a Post Doc position at the Physics Department of Polytechnic of Milan, where, since 2010, he has assumed the role of researcher. He worked on the development of the laser lidar system for the ATLID satellite founded by the European Space Agency. His current research activity concerns the development of laser sources and solid state amplifiers in the near and mid-infrared for ultra-high resolution molecular spectroscopy.

Near and Mid infrared solid-state lasers and amplifiers

Widely tunable solid-state lasers are fundamental tools to deeply understand the interaction of radiation with matter. They find a natural application in various scientific fields such as condensed matter physics, biomedicine, environmental monitoring, microscopy, telecommunications, and precision measurements.

The goal of this research activity includes both the development of innovative optical sources with tunable emission in the near and mid infrared (1 to 4 µm) spectral regions and their application to high-precision molecular spectroscopy, optical radar systems (LIDAR Light Detection and Ranging), frequency metrology and precision measurements.

Development of novel solid-state lasers and amplifiers

This activity consists in the development of ultra-wide emission bandwidth solid-state sources based on laser-pumped (diode or fiber lasers) innovative fluorides crystals doped with trivalent rare earth ions (such as erbium, thulium, and holmium) or on metal transition-doped (such as chromium and iron) binary chalcogenide crystals (ZnS, ZnSe, and CdSe). The main scientific goal is the development of near- and midium-infrared optical sources with high spectral purity (ultra-low intensity and frequency noise), wide emission wavelength tunability, and in the case of pulsed sources broad emission bandwidth and ultrashort pulse duration (femtosecond). For this purpose, the most sophisticated techniques for the active stabilization of the laser frequency, phase, and intensity are adopted. 

Fig. 1 – Frequency-stabilized diode-pumped Nd:YAG laser in active Q-switching

operation for satellite LIDAR system  (ATLID-ESA program).

Main collaborations: W. Sibbett (University of St. Andrews), M. Tonelli (Università di Pisa), M. Haakestad (Norwegian Defence Research Establishment), A. Cosentino (Galileo-Selex Pomezia).

Molecular spectroscopy with optical frequency combs

Molecular spectroscopy by means of optical frequency combs

Link to the video presentation of the research activity (italian only)

Ph. D. thesis available on the topic.

Invented by the research groups headed by T. Hansch and J. Hall (Nobel prize winners in 2005) frequency combs have revolutionized the field of optical frequency metrology, allowing for absolute frequency measurements over the entire optical spectrum with a level of accuracy never achieved until then (of the order of 1 part in 10¹⁵), essentially limited by current primary references of time (cesium atomic clocks). The underlying basis of such remarkable properties is the well-known Fourier theorem, demonstrating that the spectrum of any periodic waveform is constituted by an infinite set of evenly-spaced discrete frequencies. In the case of an optical frequency comb the waveform producing such a spectrum is the electric-field profile associated to a periodical laser pulse train, such as that emitted by a mode-locked pulsed laser.

Frequency combs are currently used in many different fields. At a scientific level, optical transitions of atoms, ions and molecules have been measured with uncertainty as low as 10^-15, enabling validation of quantum-mechanical models of their energy structure as well as a variety of tests of fundamental physics, among which the analysis of possible drifts of fundamental physical constants. Optical frequency combs have also found many practical applications, in the field of optical communications, in the development of a new generation of GPS systems and as tool for massively parallel trace gas detection.

The research activity of the group lies in the field of comb-assisted molecular spectroscopy and follows three main research-lines: a technological line, devoted to the development of novel comb-based laser sources, a scientific line in the field of molecular physics, an applicative line, mostly oriented to biomedicine.

Generation of frequency combs in the mid-infrared

The emission wavelength of commercially available frequency comb synthesizers falls within the spectral range of the near infrared. A particularly intense effort is currently spent to extend this range to the mid-infrared region, whose interest grounds on the existence of a wealth of extremely intense roto-vibrational transitions that can be successfully exploited for molecule detection and identification at extremely low concentration levels. The group pioneered the synthesis of tunable mid-IR frequency combs, in the region from 5 to 12 µm, by exploiting non-linear processes of difference frequency generation. At present, in collaboration with the Vrije Universiteit in Amsterdam, the group is developing a frequency-comb synthesizer tunable over the entire fingerprint region, from 3 to 12 µm.

Collaborations:

• Vrije Universiteit, Amsterdam LaserLab, Atomic, Molecular and Laser Physics Group

Frequency comb assisted Molecular spectroscopy in the near and mid-infrared

Frequency combs, both in the near and mid-infrared, are used in conjunction with cw lasers that probe the absorption of molecules of environmental or biomedical interest. Depending on the experiment the cw laser can be either tightly locked to a frequency comb with variable rep-rate, so as to scan it against a molecular absorption profile with absolute calibration of the frequency axis, or tightly locked to the center of a molecular absorption, with the comb acting as a ruler to count its optical frequency. In this way we are able to extract spectroscopic data such as line intensity factors, pressure-broadening and pressure-shift coefficients, and to infer accurate information on the energy-level structure of molecules, to be used either for a deeper understanding of the structure itself or for improving the accuracy of currently used databases such as HITRAN. Recently, through the use of resonant cavities with high finesse, we are planning to boost the sensitivity of the spectroscopic setup, so as to move towards the study of molecular lines with extremely low intensity, such as those of homonuclear molecules with no electric dipole moment.

Collaborations:

• Environmental Sciences Department, Second University of Naples (Italy)
• IMRA America Inc., Ann Arbor (Michigan, USA)

Direct comb spectroscopy for quantitative analysis of human breath

A third research-line, more application-oriented, aims at the development of a new class of spectrometers capable of detecting multiple molecular species with broad spectral coverage, short acquisition time, and high sensitivity. This research line opens up new possibilities in several areas, especially in the field of human breath analysis, which is a powerful non-invasive diagnostic perspective of various kinds of diseases. In such case the use of a single cw laser is not adequate, since not allowing for parallel detection of multiple biomarkers or for molecular identification of complex molecules with broad and congested absorption spectra. On the other hand frequency combs, because of their peculiar spectral structure - stable, discrete and controllable, can be directly coupled into high finesse optical cavities. By proper spectral detection of the cavity output, multi-species detection becomes possible together with sensitivity at the few parts per billion level and acquisition times of the order of few seconds.