High Gain Solid-State Amplifiers for Picosecond Pulses

We review solid-state laser amplifiers for generation of intense picosecond pulses, in various regimes from single shot to repetition rates of GHz. Such laser sources are becoming increasingly attractive for many industrial and scientific applications. In particular, we have exploited the technology of side-pumped grazing-incidence bounce amplifiers. Such amplifiers yield very high gain per pass, up to several thousands, and offer excellent beam quality preservation owing to the total reflection leading to left-right inversion. This technology allows the realization of compact, efficient and modular amplifiers, significantly simpler than, for example, cavity-based regenerative schemes. Starting from robust, low-power diode-pumped solid-state oscillators, using programmable pulse-pickers one can select either a single pulse or a properly shaped pulse train for further amplification and compensation of envelope distortions due to gain saturation. For single pulse amplification it is preferred to start with a relatively low-repetition-rate oscillator (< 100 MHz). Picosecond fiber oscillators are most promising in this respect. Using quasi-cw diode arrays as the pump source of Nd:YVO4 slab amplifier, starting from ≈ 1 nJ, 10-ps pulse seed, amplified pulse energy as high as 200 μJ at 1 kHz can be obtained. Efficient harmonic and traveling-wave parametric generation are readily achieved with such high pulse peak powers. Some other applications require instead the amplification of pulse trains, that can be conveniently extracted and amplified from a low-power oscillator at the desired repetition rate. For example, starting from a 20-mW, 5-GHz picosecond oscillator we amplified trains of few thousands of pulses up to 2 mJ with three slab amplifiers (as much as 300 mJ were achieved with two additional Nd:YAG flash-lamp-pumped post-amplifiers). Such pulse trains are very effective for synchronous pumping of optical parametric oscillators, lowering significantly their threshold with respect to the traveling-wave geometry. When multi-MHz picosecond pulses are required, cw diode arrays are chosen as pump sources for the slab amplifiers. An 8-W, 8-ps laser system has been demonstrated starting from a 50-mW cw oscillator, at 150 MHz. Owing to the effective gain shaping of the tightly pumped amplifier, no significant thermal distortion were detected, allowing nearly diffraction limited operation. Although high power picosecond oscillators have been demonstrated lately, this result is interesting since it suggests an alternative way for power-scaling of picosecond sources without pushing delicate intracavity components (such as semiconductor saturable absorbers) to the damage limit. Numerical models of the amplifiers and their dynamics are also reviewed. The effects of amplified spontaneous emission are discussed, as well as the most effective methods for its suppression

Narrowband, mid-infrared, seeded optical parametric generator based on non-critical CdSiP2 pumped by 120-ps, single longitudinal mode 1,064 nm pulses

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Sub-nanosecond, 1-10 kHz, low-threshold, non-critical OPOs based on periodically poled KTP crystal pumped at 1,064 nm

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Laser system generating 250-mJ bunches of 5-GHz repetition rate, 12-ps pulses.

We report on a high-energy solid-state laser based on a master-oscillator power-amplifier system seeded by a 5-GHz repetition-rate mode-locked oscillator, aimed at the excitation of the dynamic Casimir effect by optically modulating a microwave resonator. Solid-state amplifiers provide up to 250 mJ at 1064 nm in a 500-ns (macro-)pulse envelope containing 12-ps (micro-)pulses, with a macro/micropulse format and energy resembling that of near-infrared free-electron lasers. Efficient second-harmonic conversion allowed synchronous pumping of an optical parametric oscillator, obtaining up to 40 mJ in the range 750-850 nm

Design and Development of the Folded 4-Mirror Resonators for Diode End-pumped Solid-State Cr:LiSAF Laser

We present the design and development of folded four-mirror resonators for diode end-pumped solid-state Cr:LiSAF lasers. The astigmatic effects due to the Brewster-cut laser crystal and two curved mirrors used at oblique incidence were taken into consideration. The obtained results showed the stability regions of resonator, the beam parameters in the resonator and within the laser crystal as well as other sensitive parameters and their variation ranges. Furthermore, the designed folded four-mirror resonators for diode end-pumped Cr:LiSAF laser were experimentally evaluated. The CW Cr:LiSAF laser characteristics in threshold, efficiency and beam quality as well as comparative studies are presented

Diode-pumped Nd: BaY 2 F 8 picosecond laser mode-locked with carbon nanotube saturable absorbers

Picosecond pulse generation near 1-m wavelength has been achieved with a Nd: BaY 2 F 8 (Nd:BaYF) laser mode-locked using a single-walled carbon nanotube saturable absorber (SWCNT-SA). The laser was operated at its main 1049-nm transition, generating 8.5-ps pulses with Ϸ70-mW output power for Ϸ570-mW absorbed pump power. This is the first demonstration of cw mode-locking in the picosecond regime with Nd-doped crystals and SWCNT-SAs. The requirements on the SWCNT-SA for successful mode-locking in relatively narrowband neodymium lasers are reviewed and their implications are discussed

Colorectal Cancer Stage at Diagnosis Before vs During the COVID-19 Pandemic in Italy

IMPORTANCE Delays in screening programs and the reluctance of patients to seek medical attention because of the outbreak of SARS-CoV-2 could be associated with the risk of more advanced colorectal cancers at diagnosis. OBJECTIVE To evaluate whether the SARS-CoV-2 pandemic was associated with more advanced oncologic stage and change in clinical presentation for patients with colorectal cancer. DESIGN, SETTING, AND PARTICIPANTS This retrospective, multicenter cohort study included all 17 938 adult patients who underwent surgery for colorectal cancer from March 1, 2020, to December 31, 2021 (pandemic period), and from January 1, 2018, to February 29, 2020 (prepandemic period), in 81 participating centers in Italy, including tertiary centers and community hospitals. Follow-up was 30 days from surgery. EXPOSURES Any type of surgical procedure for colorectal cancer, including explorative surgery, palliative procedures, and atypical or segmental resections. MAIN OUTCOMES AND MEASURES The primary outcome was advanced stage of colorectal cancer at diagnosis. Secondary outcomes were distant metastasis, T4 stage, aggressive biology (defined as cancer with at least 1 of the following characteristics: signet ring cells, mucinous tumor, budding, lymphovascular invasion, perineural invasion, and lymphangitis), stenotic lesion, emergency surgery, and palliative surgery. The independent association between the pandemic period and the outcomes was assessed using multivariate random-effects logistic regression, with hospital as the cluster variable. RESULTS A total of 17 938 patients (10 007 men [55.8%]; mean [SD] age, 70.6 [12.2] years) underwent surgery for colorectal cancer: 7796 (43.5%) during the pandemic period and 10 142 (56.5%) during the prepandemic period. Logistic regression indicated that the pandemic period was significantly associated with an increased rate of advanced-stage colorectal cancer (odds ratio [OR], 1.07; 95%CI, 1.01-1.13; P = .03), aggressive biology (OR, 1.32; 95%CI, 1.15-1.53; P &lt; .001), and stenotic lesions (OR, 1.15; 95%CI, 1.01-1.31; P = .03). CONCLUSIONS AND RELEVANCE This cohort study suggests a significant association between the SARS-CoV-2 pandemic and the risk of a more advanced oncologic stage at diagnosis among patients undergoing surgery for colorectal cancer and might indicate a potential reduction of survival for these patients

Approximate solution for high-frequency Q-switched lasers

A simple approximation for the energy, pulse width, and build-up time valid for high-repetition-rate Q-switched lasers is discussed. This particular regime of operation is most common in industrial applications where manufacturing time must be minimized. Limits of validity and some considerations for the choice of the most appropriate laser system for specific applications are briefly discussed

Beam splitter phase shifts: Wave optics approach

We investigate the phase relationships between transmitted and reflected waves in a lossless beam splitter having a multilayer structure, using the matrix approach as outlined in classical optics books. Contrarily to the case of the quantum optics formalism generally employed to describe beam splitters, these matrices are not unitary. In this note we point out the existence of general relations among the elements of the transfer matrix that describes the multilayer beam splitter. Such relations, which are independent of the detailed structure of the beam splitter, fix the phase shifts between reflected and transmitted waves. It is instructive to see how the results obtained by Zeilinger by using spinor algebra and Pauli matrices can be easily derived from our general relations

Chapter High Gain Solid-State Amplifiers for Picosecond Pulses

Biotechnolog