Intracavity intensity noise suppression in the inverse Compton scattering source BriXSinO exploiting carrier-envelope offset manipulation

We report on a technique that exploits the control of the carrier -envelope offset to suppress the frequency-to-intensity noise conversion in the locking of a mode-locking laser against a high-finesse optical enhancement resonator. A proper combination of the laser carrier-envelope offset and the resonator finesse allows the improvement of the signal-to-noise ratio of the optical intensity trapped into the optical resonator. In this paper, we show the application of this technique in the laser system of the inverse Compton scattering source BriXSinO, currently under development in Milan, Italy, demonstrating the possibility of achieving an intracavity intensity noise reduction of a factor of 20

Primary gas thermometry by means of laser-absorption spectroscopy: Determination of the Boltzmann constant

We report on a new optical implementation of primary gas thermometry based on laser absorption spectrometry in the near infrared. The method consists in retrieving the Doppler broadening from highly accurate observations of the line shape of the R(12) $\nu_{1} + 2 \nu_{2}^{\phantom{1}0} + \nu_{3}$ transition in CO$_{2}$ gas at thermodynamic equilibrium. Doppler width measurements as a function of gas temperature, ranging between the triple point of water and the gallium melting point, allowed for a spectroscopic determination of the Boltzmann constant with a relative accuracy of $\sim1.6\times10^{-4}$.Comment: Submitted to Physical Review Letter

Carrier-envelope offset frequency measurement by means of an external optical resonator

A general-purpose method based on the implementation of the asymmetric Pound-Drever-Hall (PDH) technique is proposed to measure the carrier-envelope offset (CEO) frequency of a mode-locked laser using an external optical cavity. By analyzing the synchronously demodulated signal of the spectrally filtered cavity reflection when the optical resonator is locked to the mode-locked laser, a discriminating signal depending on the relative frequency offset between the mode-locked and optical cavity comb-like spectra is obtained. For a given geometry and group delay dispersion (GDD) of the cavity parameters (i.e., a known cavity mode offset), this signal can be used to retrieve the laser CEO. This approach turns out to be advantageous in terms of setup complexity with respect to other well-known techniques that rely on non-linear frequency generation, such as f-2f interferometers. In addition, this method can be used to precisely determine the laser-cavity spectral coupling, which is an important topic in cavity-enhanced spectroscopy and non-linear optics applications. After the theoretical description of the generalized asymmetric PDH signal, an experimental validation of the proposed method is reported using an Er-doped fiber frequency comb source centered at 1,550 nm, with a repetition rate of 250 MHz, locked to a linear optical cavity with a 1 GHz free spectral range. The theoretical effect of the GDD is confirmed experimentally using different cavity configurations. Moreover, the comparison with the CEO frequency values measured using an f-2f interferometer demonstrates the feasibility of the proposed method

Passive mode locking of a Tm,Ho:KY(WO4)(2) laser around 2 μm

We report the first demonstration, to our knowledge, of passive mode locking in a Tm3+, Ho3+-codoped KYWO42 laser operating in the 2000-2060 nm spectral region. An InGaAsSb-based quantum well semiconductor saturable absorber mirror is used for the initiation and stabilization of the ultrashort pulse generation. Pulses as short as 3.3 ps were generated at 2057 nm with average output powers up to 315 mW at a pulse repetition frequency of 132 MHz for 1.15 W of absorbed pump power at 802 nm from a Ti:sapphire laser

Comb-assisted spectroscopy of CO2 absorption profiles in the near- and mid-infrared regions

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Mid-IR tunable CW and passively Q-switched laser operation of Dy-doped fluoride fiber

We report a comprehensive characterization of tunable continuous-wave (CW) and passive Q-switching laser performance of Dy-doped zirconium fluoride fiber emitting around 3 mu m. The in-band pumped CW laser operation is investigated for pump wavelengths varying from 2.7 mu m to 2.825 mu m, for fiber lengths ranging from 0.4 m to 2 m, and for output coupling efficiency from 10% to 50%, leading to a maximum laser slope efficiency of 44% and a tuning range larger than 300 nm. With Findlay-Clay analysis and Rigrod analyses, optimal cavity parameters are retrieved, paving the way for further optimizations in performance. The passively Q-switched laser operation of Dy-doped fluoride fiber is achieved employing a semiconductor saturable absorber mirror for the first time, demonstrating a stable operation with a minimum pulse duration of 580 ns, a highest repetition frequency of 103 kHz and a pulse energy up to 300 nJ

Cavitation phenomenon in mechanical prosthetic valves: Not only microbubbles

Introduction: Microbubbles (MBs) or cavitation is high-velocity, echo-bright findings present during the closing or opening of a mechanical valve (MVP). Cavitation bubble growth or gas emboli are less frequently described. We evaluated the hemodynamic parameters involved in the formation of gas emboli and the impact of gas emboli on requests for additional investigations. Methods and Results: Transthoracic echocardiographic studies (TTE) of 57 patients (31 males, mean age 46.8\ua0\ub1\ua013.8\ua0years) with gas emboli were evaluated after heart valve replacement surgery. The majority (72%, n\ua0=\ua042) had a mitral or combined mitral/aortic MVP, with 28% (n\ua0=\ua016) an aortic MVP. The last TTE with and without gas emboli were considered for the same patient and the no emboli group was the control group (42 patients). The patient's blood pressure (BP) and heart rate (HR) were available for each TTE. Comparing the two TTEs, the systolic and diastolic BP, transmitral and aortic gradients, and left ventricular ejection fraction were similar but the HR (80.9\ua0\ub1\ua018.7 vs 72.5\ua0\ub1\ua013.9\ua0bpm, P\ua0=.02) was significantly higher in the group with gas emboli. A TEE was performed 52 times in 27 patients, due to gas emboli, with one case positive for thrombus/vegetation. For 19 patients, a brain CT was requested. In two patients, the indication for the brain CT was gas emboli but the result was negative. Conclusion: Gas emboli are frequently present and associated to an increased HR. They can cause the misdiagnosis of endocarditis or thrombus formation with significant additional requests for diagnostic examinations

Er:Yb phosphate glass laser with nonlinear absorber for phase-sensitive optical time domain reflectometry

A novel laser for phase-sensitive optical time-domain reflectometry (Φ-OTDR) is presented. The advantages of a compact solid-state laser are listed, current problems are shown. Experiments with a microchip single-optical-element laser, from setup construction to usage in Φ-OTDR system, are presented. New laser scheme with two-photon intracavity absorber is suggested and its advantages are described