Stefano Dell'Acqua - Academia.edu (original) (raw)

Papers by Stefano Dell'Acqua

The goal of UTOFIA (EU H2020 project) is to offer a compact and cost-effective underwater imaging... more The goal of UTOFIA (EU H2020 project) is to offer a compact and cost-effective underwater imaging system for turbid environments. Using range-gated imaging, the system will extend the imaging range by factor 2 to 3 over conventional imaging systems, while at the same time providing video-rate 3D information. This will fill the current gap between short-range, high-resolution conventional video and long-range low-resolution sonar systems. UTOFIA offers a new modus operandi for the main targeted domains of application: marine life monitoring, harbor and ocean litter detection, fisheries stock assessment, aquaculture monitoring, and seabed mapping. A novel, frequency doubled laser system emitting @532nm to be used as scene illuminator is the main result of this presentation. The laser is based on a completely new conceptual design necessary to meet the tougher laser specifications as emerged after the successful results obtained with a preliminary off-the-shelf source (SystemZero implementation) and the prospected requirements for enhancing UTOFIA imaging system competitiveness. The new laser presents a novel MOPA (master oscillator-power amplifiers) architecture, chosen in order to render the output energy scalable in the present and future upgrades. The energy, pulse duration, and repetition rate goals sought for this item have been achieved: >2mJ @532nm, <;2ns, up to 1kHz. Other issues have been addressed and successfully managed with this new laser implementation: very compact packaging, low power consumption, and efficient cooling under a wide range of operating environmental conditions. Two more features, important for optimal imaging operation of the system, are the ability of the laser to operate in low temporal jitter when triggered by the video-camera signals in order to cope with the correct range-gating temporization and a refined optical beaming that allows a versatile control of the scene illumination over a wider range of distances and angular span.

Optics Letters, 2004

We report on a diode-pumped 1.3-mm Nd:GdVO 4 cw laser, intracavity doubled for highly efficient g... more We report on a diode-pumped 1.3-mm Nd:GdVO 4 cw laser, intracavity doubled for highly efficient generation of red light. We obtained as much as 2.4 W of power at 670 nm (corresponding to 26% optical-to-optical efficiency) in a nearly TEM 00 mode and with small amplitude noise. To the best of our knowledge, these results represent the highest performance at this wavelength for cw solid-state lasers.

Optics Express, 2003

We report what is to our knowledge the first Nd:BaY 2 F 8 (Nd:BaYF) laser pumped with a multiwatt... more We report what is to our knowledge the first Nd:BaY 2 F 8 (Nd:BaYF) laser pumped with a multiwatt fiber-coupled diode array tuned at ≈804 nm. As much as 2.4 W were obtained with 6.2 W of absorbed pump power, showing efficient operation (51% slope efficiency), excellent beam quality (M 2 =1.1), and weak thermal lensing. Small intracavity losses (<1%) were measured, indicating both reduced thermally induced aberrations and good optical quality of the laser crystal.

Optics Communications, 1997

ABSTRACT

Optics Communications, Jun 1, 1996

We developed an all-solid-state Cr4+:forsterite laser pumped by a kHz Q-switched diode-pumped Nd:... more We developed an all-solid-state Cr4+:forsterite laser pumped by a kHz Q-switched diode-pumped Nd:YAG oscillator. The laser is tunable from 1190 to 1310 nm, and generates pulses with duration &ap; 70-100 ns and maximum energy &ap; 14 muJ at 1230 nm, corresponding to a pumping efficiency &ap; 10%. This system could be employed as a regenerative amplifier in an ultrafast all-solid-state

IEEE Journal of Selected Topics in Quantum Electronics, 1997

We report on the experimental results of a continuously diode-laser pumped Nd:YAG laser, operatin... more We report on the experimental results of a continuously diode-laser pumped Nd:YAG laser, operating at 1064 nm and repetitively Q-switched by a Cr 4+ :YAG solid-state saturable absorber. End-pumping the Nd:YAG with a 10-W fiber-coupled diode-laser we could either optimize the energy or the average output power, depending on the choice of the saturable absorber and the output coupler. The maximum energy was 200 J in single TEM00, 17 ns pulses at 6 kHz, whereas a maximum average power of 2 W with 32-ns pulses at 20 kHz was obtained. We also present preliminary results of a repetitively Qswitched Nd:YVO4 laser at 1064 nm. The repetitive Q-switching operation is described by an improved model, which accounts for the behavior of both the active medium and the solid-state saturable absorber. The results of the model agree fairly well with the experimental data. Experimental results of second harmonic conversion are also reported and interpreted using a depleted pump model.

Applied optics, Jan 20, 1997

We report on the experimental results of a diode-pumped, intracavity-doubled cw Nd:YAG laser, pum... more We report on the experimental results of a diode-pumped, intracavity-doubled cw Nd:YAG laser, pumped by a 10-W fiber-coupled semiconductor laser at 808 nm and emitting as much as 600 mW in a stable single longitudinal mode and TEM(00) spatial mode. We discuss the main issues of the resonator design and the optimization of the intracavity second harmonic conversion by interpreting our results using simple models. Improvements for the current project are also discussed.

Advanced Solid State Lasers, 2000

Neodymium doped germanates with a garnet structure, such as Nd:Ca3Sc2Ge3O12 (Nd:CaSGG [l]), are p... more Neodymium doped germanates with a garnet structure, such as Nd:Ca3Sc2Ge3O12 (Nd:CaSGG [l]), are promising laser materials for diode-pumping.

Filtration Industry Analyst, 2000

Summary form only given. Fluorescence spectra of Nd3+2% wt in CNGG (formula Ca3(GaNb)2-xGa3O 12) ... more Summary form only given. Fluorescence spectra of Nd3+2% wt in CNGG (formula Ca3(GaNb)2-xGa3O 12) were recorded at temperatures ranging from 10 and 298 K, for 0.9 μm, 1.06 μm, 1.32 μm bands. The room temperature absorption spectra from 300 to 2700 nm show broad band structures, the 807 nm peak has α=10 cm-1 with FWHM of 7 nm (8 times

Conference Digest. 2000 Conference on Lasers and Electro-Optics Europe (Cat. No.00TH8505)

ABSTRACT YAG:V crystals have been recently proposed as solid-state saturable absorbers for Q-swit... more ABSTRACT YAG:V crystals have been recently proposed as solid-state saturable absorbers for Q-switched neodymium lasers at 1-1.3 μm. We report what we believe to be the first investigations on high-power passively Q-switched Nd:YAG, Nd:YAP and Nd:YVO4 lasers operated at 1.3 μm. These are known as the most efficient and readily available laser media at this wavelength. The pump source was a 12-W fiber-coupled diode array emitting near 810 nm

2003 Conference on Lasers and Electro-Optics Europe (CLEO/Europe 2003) (IEEE Cat. No.03TH8666)

This article presents a new approach for efficient generation of high quality red light, exploiti... more This article presents a new approach for efficient generation of high quality red light, exploiting intracavity doubled CW neodymium lasers pumped with highly reliable and relatively low-cost 808 nm diode arrays. Significant advances in the development of a compact solid-state source at 670 nm, yielding a 2.4-W beam nearly TEM/sub 00/, with /spl ap/9.2-W absorbed pump power at 806 nm are presented.

Novel Lasers and Devices-Basic Aspects, 1999

Journal of the Optical Society of America B, 1999

We report the development of compact, efficiently diode-pumped Nd:YAG and Nd:YAlO 3 lasers in a p... more We report the development of compact, efficiently diode-pumped Nd:YAG and Nd:YAlO 3 lasers in a pulsed regime, mode locked by a nonlinear mirror (NLM) technique. Pumping with an 80-W single-bar diode array at a repetition rate as high as 200 Hz and depending on the NLM configuration, trains of 20-100 pulses, with 25-ps pulses with energies as high as 9 J each, are generated. These novel pulsed picosecond sources show excellent amplitude stability (Ͻ2% amplitude fluctuation) and beam quality. Numerical simulations of the pulse-formation dynamics are presented, and the results are compared with the experiments.

IEEE Journal of Quantum Electronics, 2001

We have exploited the broad absorption and emission bandwidth of the laser crystal Ca 3 (NbGa) 2 ... more We have exploited the broad absorption and emission bandwidth of the laser crystal Ca 3 (NbGa) 2 Ga 3 O 12 doped with Nd 3+ to develop a tunable and mode locked diode-pumped 1 06 m laser. We also present the fluorescence and excitation spectra at different crystal temperatures from 10 to 298 K. The spontaneous transition probabilities, the branching ratios, and the radiative lifetime are calculated by means of the Judd-Ofelt theory and compared with the experimental results. The stimulated emission cross-sections of the most important transitions have been calculated and compared with laser results. Employing a 2-W laser diode as a continuous-wave pump source, we have been able to tune the emission wavelength in the range 1053-1074 nm. Active mode-locking yielding pulses of 9.6, 18, and 19.7 ps at the three main emission peaks of 1058.6, 1061.2, and 1065.3 nm, respectively, was also demonstrated.

IEEE Journal of Quantum Electronics, 1998

High average power compact sources of nanosecond pulses at kilohertz repetition rate are interest... more High average power compact sources of nanosecond pulses at kilohertz repetition rate are interesting for many practical applications, each requiring a specific operating wavelength. Cr:YAG solid-state saturable absorbers recently proved to be particularly attractive for the development of compact high-power Q-switched diode-pumped lasers1,2.

Applied Physics B, 2000

We report on a passively Q-switched diodepumped Nd:YAG laser including an intracavity optical par... more We report on a passively Q-switched diodepumped Nd:YAG laser including an intracavity optical parametric oscillator, that generates 120-µJ pulses with 1.6 ns time duration (75 kW peak power) at 1572 nm with excellent beam quality (M 2 ≈ 1.1) and pulse amplitude fluctuation ≈ 2%. The passively Q-switched laser alone, pumped by a 200-Hz repetition rate, 80-W peak-power single diode bar, produced linearly polarized pulses of 12 ns and 460 µJ energy at 1064 nm. A different, more complex cavity setup optimizing the passive Q-switching yielded 160-µJ 2-ns signal pulses with slightly increased peak power.

Applied Physics B: Lasers and Optics, 2003

We report on a passively Q-switched diode-pumped Nd:YVO 4 laser polarized along the a axis (corre... more We report on a passively Q-switched diode-pumped Nd:YVO 4 laser polarized along the a axis (corresponding to the smallest value of emission cross section at 1064 nm), generating 157-µJ pulses with 6.0-ns time duration (> 20 kW peak power) and 3.6 W of average power at 1064 nm with good beam quality (M 2 < 1.4). The selection of the polarization was performed by a novel technique relying on the birefringence of the laser crystal and on the misalignment sensitivity of the resonator.