Optical Measurements and Laser Instrumentation

Misure Ottiche ed Optoelettroniche

Via Ponzio, 34/5, 20133 Milano, ITALY

Tel. +39 02 2399 3421,  Fax +39 2399 3413












The research group covers different aspects of optical measurements ranging from laser development and characterization, optical frequency standards in the near infrared (NIR), optical sensors and instrumentation, 3D laser scanning and image reconstruction, electrooptical measurements, to specific electronic and biomedical measurement systems.

The main research topic is on laser amplitude and frequency noise characterization and active stabilization of the optical oscillator by means of optoelectronic control loops. To achieve frequency/wavelength stabilization, absolute frequency references (atoms/molecules) are used in conjunction with high-resolution laser spectroscopy, allowing the group for pioneering some optical frequency standards at the international level. This activity ─ often pursued in cooperation with the Department of Physics of this Polytechnic University (FIS-PoliMI) and with other Italian or International Research Centers and Metrological Institutes {National Metrology Institute of Japan (NMIJ‑JP) part of the Institute of Advanced Industrial Science and Technology (AIST‑JP), Tel Aviv University (TAU‑IL), National Institute of Metrological Research (I.N.RI.M.‑IT), Istituto di Fotonica e Nanotecnologie (IFN‑CNR‑IT), Physikalisch‑Technische Bundesanstalt (PTB‑DE), Danish Fundamental Metrology (DFM‑DK)} ─ took advantage from working at the development of novel diode-pumped solid-state lasers operating in the NIR spectral region. These non-commercial optical oscillators need to be particularly suitable (wide wavelength tunability and capability of single‑mode frequency control) for NIR high-resolution spectroscopy and frequency locking to molecular absorption lines. The study, development, throughout characterization, and frequency stabilization of such new laser sources is an important part of this research activity and also provides good aid to the international visibility of the group. Frequency doubling of diode‑pumped solid‑state NIR lasers can provide for a few milliwatt of coherent radiation in the 505‑515 nm spectral region, useful for laser spectroscopy and frequency locking against iodine (I2) lines. In this particular wavelength region, future optical frequency standards are being worldwide investigated since I2 natural linewidths are here narrowest (~50 kHz) and hence more suitable for a frequency reference. Working with Prof. Bava and Dr. Galzerano, both formerly part of the group, we also theoretically studied the effects of laser amplitude and frequency noise in optical frequency discriminators based on Fabry‑Pérot interferometers and the FM frequency‑locking technique .

Research on optical sensors, based on the laser self-mixing process or other interferometric techniques, is a second important task pursued by the group ─ sharing since years a profitable collaboration with the group of Prof. S. Donati at the University of Pavia ─ and allows for interesting scientific results at the international level, also opening the way to applied-optics R&D and Technology Transfer to the industry. The measurement method based on optical self‑mixing of the backreflected radiation within a semiconductor laser diode is a method pioneered by M. Norgia, S. Donati, T. Bosch and coworkers. The laser source for such self‑interferometric detection can be a common semiconductor laser, opening the way to practical and off‑Lab. high‑resolution sensing applications [4]. A more recent cooperation in the field of optical sensors is with the Department of Mechanics of this Polytechnic, aiming at the characterization of water-jet cutting machines and, in particular, at measuring water velocities up to 1000 m/s by simple and novel electrooptical techniques.

Other research topics covered by the group ─ in cooperation with the Institute of Biomedical Engineering (IsIB) of the Nation Research Council (CNR) in Italy ─ are in the field of medical measurements and applications. Here, the activity is oriented on one side at 3D laser scanning and image reconstruction of anatomical parts or prostheses, and on the other side at the electrical characterization “in vitro” of the electric field potentials generated by cochlear implants.

In recent years the group underwent significant personnel changes, since Prof. Elio Bava (founder and formerly leader of this research group) left PoliMI-DEI in year 2004 as becoming the President of the I.N.RI.M. in Turin. Also Dr. Gianluca Galzerano, who was with the group since 1994, left the DEI‑PoliMI in year 2001 for a permanent position at CNR and FIS-PoliMI. Even if these researchers are no more physically present at DEI-PoliMI, the research cooperation with both Elio Bava and Gianluca Galzerano (FIS-PoliMI is only at 300 m distance from DEI-PoliMI) is still strongly active and very profitable for the research group.