Diode Pumped Solid State (DPSS) Lasers, Ultrafast Lasers and Special Sources
Federico Pirzio, Luigi Fregnani and Simone Tacchini

During the 1990s, the impressive increase of telecommunications market gave incentive to the spread of optical devices and to the improvements in semiconductor growth technology, allowing a decisive step forward to semiconductor diode laser performances. The availability of new compact, reliable and efficient diode pump modules made easier the rapid growth of DPSSL (Diode Pumped Solid State Lasers), now representing the state of the art for the industrial market.
The Laser Source Laboratory (LSL) pioneered in Italy the research in this field and it is nowadays a well experienced group in the development of innovative solutions in the field of DPSSL. In the last decades, our group has accumulated a huge experience in almost all the expects involved in the design of efficient DPSSL systems. Pumping schemes, resonator modeling, thermal problems, active and passive Q-Switching and mode-locking techniques have been intensively investigated. Research in this field is still going on.

In the last few years we especially focussed on:
- the study of new Nd and Yb doped materials for ultrashort (picosecond and femtosecond) pulse generation;
- the study of new nanostructured saturable absorbers for ultrashort pulse generation;
- the numerical modeling and the experimental realization of compact and highly efficient amplifiers for nanosecond and picosecond pulses at 1 µm;
- the development of highly customized and extremely complex laser systems within national and international research projects.

High-Power Ultrafast Lasers and Amplifiers
Federico Pirzio and Simone Tacchini

High-power, ultrafast lasers technology has rapidly progressed over the past two decades. Thanks to a continual academic and industrial research, the cost and complexity of ultrafast lasers progressively decreased, making this technology available for a large, and rapidly increasing, variety of bio-medical and industrial applications.
The state of the art in this field is represented by high power femto-second diode-pumped lasers emitting in the 1 µm wavelength region. These laser systems usually rely on Yb-doped crystals as active media, since Yb ion offers a small quantum defect (that results in higher efficiencies and potential for average power up-scaling) and a very broad emission bandwidth, a fundamental prerequisite for ultrashort pulse generation.
This research field is characterized by a strong interconnection with the industrial laser market. At the LSL, also through active and fruitful collaborations with important international companies, we investigate the potential of new Yb-doped active materials and study innovative solutions for femtosecond high-power amplifiers.

Fiber Lasers and numerical modelling
Federico Pirzio and Luca Tartara

In the last years, fiber lasers have increasingly gained market positions previously occupied by other kinds of laser sources. The single-mode (high beam quality) operation, broad emission linewidth, high gain (expecially in MOPA configuration), high optical/electrical conversion efficiency, easy thermal managment, industrial reliability, low cost and the continuous increase in output power (kW level in CW operation) represent the main fatures which lead fiber lasers to be an attractive solution in many industrial and scientific applications such as: material processing, spectroscopy, medicine, telecommunications etc... In particular, at LSL we focus on passively (SESAM) mode-locked operation at 1 µm mainly in the picosecond region (1÷100 ps) for micromachinig application or nonlinear frequency conversion to directly access the mid-IR spectral range (up to 10 μm). Furthermore, numerical (MATLAB) models are continuously under development to allow better fiber amplifier and laser design.

Nonlinear Optics
Federico Pirzio, Alessandra Tomaselli and Luca Tartara

Many applications would benefit of the availability of coherent radiation in spectral region not covered at all, or extremely difficult to access with conventional laser sources. For instance, visible and UV laser sources play a crucial role in material processing and high precision manufacturing, whereas the InfraRed and Mid-Infrared spectral region are increasingly important for bio-medical, military and scientific applications.
The high peak power of ultrafast laser pulses reliably generated by DPSSL operating at 1 µm, can be exploited to efficiently excite a variety of nonlinear (NL) effects. Frequency up conversion can be realized through harmonic generation, whereas frequency down conversion can be obtained through optical parametric generation/amplification and stimulated Raman scattering.
At the LSL we both do industry-oriented and academic research in this field. We design and realize efficient frequency up and down conversion stages based on standard, market available NL materials, and we also have the opportunity to test and qualify new and very promising non-linear crystals, fully exploiting our expertise in the design of the pump laser sources also. Several international collaboration are open on this research topic. Nonlinear optical microscopy is also a subject of investigation of our research group.