Search

In quantum cascade laser frequency combs, the intensity distribution of the optical spectrum can be split into two well-separated lobes of longitudinal modes that, even when far apart, have a common phase relation and preserve equal frequency separation. The temporal dynamics of two lasers emitting at 4.4 and 8.1 µm operating in this bilobed regime are here investigated. The laser intensity shows a peculiar temporal behavior associated with the spectral features whereby, every half a round-trip, the total emitted power switches from one lobe to the other, with a perfect temporal anti-correlation. The anti-correlation between the lobes is also observed in the intensity noise figure of the emission. This coherent phenomenon arises from gain nonlinearities induced by spatial hole burning and the extremely fast gain dynamics typical of quantum cascade lasers. [ABSTRACT FROM AUTHOR]

Small-scale Fourier transform spectrometers are rapidly revolutionizing infrared spectro-chemical analysis, enabling on-site and remote sensing applications that were hardly imaginable just few years ago. While most devices reported to date rely on advanced photonic integration technologies, here we demonstrate a miniaturization strategy which harnesses unforced mechanisms, such as the evaporation of a liquid droplet on a partially reflective substrate. Based on this principle, we describe a self-operating optofluidic spectrometer and the analysis method to retrieve consistent spectral information in spite of the intrinsically non-reproducible droplet formation and evaporation dynamics. We experimentally realize the device on the tip of an optical fiber and demonstrate quantitative measurements of gas absorption with a 2.6 nm resolution, in a 100 s acquisition time, over the 250 nm span allowed by our setup's components. A direct comparison with a commercial optical analyzer clearly points out that a simple evaporating droplet can be an efficient small-scale, inexpensive spectrometer, competitive with the most advanced integrated photonic devices. Compact spectrometers can be useful in many applications and many sophisticated architectures have been proposed. In this work, the authors show that with an evaporating droplet on a fiber tip, spectrometry can be robustly and accurately performed with a simple and passive microfluidic system. [ABSTRACT FROM AUTHOR]

In view of high-precision molecular spectroscopy in the infrared, we realized a narrow-linewidth laser source at 5.8 μ m traceable to the second in the International System of Units by mixing two near-infrared lasers in an orientation-patterned GaP crystal. The generated radiation is traceable to a Cs fountain through an optical fiber-delivered carrier; its estimated linewidth is 2.3 kHz at 1 s integration time. A quantum cascade laser emitting at the same wavelength is used to boost the power of the mid-IR radiation up to few tens of mW. Thanks to a phase-locking loop, about 70% of the quantum cascade laser output power is within the linewidth of the difference-frequency radiation. This apparatus is used for absolute molecular spectroscopy in a region, above 5 μ m, where high-precision traceability and reliable operation are still challenging. In this paper, we provide the basic information to implement a powerful and metrological grade source in the mid-infrared for precision measurements. [ABSTRACT FROM AUTHOR]

The electric quadrupole fundamental (v=1←0) band of molecular deuterium around 3 μm is accessed by cavity ring-down spectroscopy using a difference-frequency-generation source linked to the Cs-clock primary standard via an optical frequency comb synthesizer. An absolute determination of the line position and strength is reported for the first two transitions (J=2←0 and J=3←1) of the S branch. An accuracy of 6×10-8 is achieved for the line-center frequencies, which improves by a factor 20 previous experimental results [A. R. W. McKellar and T. Oka, Can. J. Phys. 56, 1315 (1978)]. The line strength values, measured with 1% accuracy, are used to retrieve the quadrupole moment matrix elements which are found in good agreement with previous theoretical calculations [A. Birnbaum and J. D. Poll, J. Atmos. Sci. 26, 943 (1969); J. L. Hunt, J. D. Poll, and L. Wolniewicz, Can. J. Phys. 62, 1719 (1984)]. [ABSTRACT FROM AUTHOR]

We investigate the characteristics of the poling process of two samples of Er:LiNbO3 grown by the Chzocralski technique by comparing their optical properties. The first has a multidomain structure and shows some optical inhomogeneities probably due to lattice defects; the second, poled at the high temperature just after the growth, has a ferroelectric monodomain structure. Moreover, in order to highlight the effect of the high temperature poling, a further poling process was performed on both the samples at room temperature and was monitored in real time through a simple optical setup in order to evidence whether the erbium inclusion influences the poling process and which are the differences between the poling dynamics of the two samples. The results show that the erbium causes a change of the coercive field value with respect to the pure congruent LiNbO3 crystals, and that the multidomain structure influences strongly the poling dynamics. [ABSTRACT FROM AUTHOR]

The fast dynamic evolution of ferroelectric domains during electric field poling in flux grown KTiOPO4 crystals was investigated online by a digital holography based technique. The dependence of the ferroelectric domain kinetics on the electric field temporal wave form and poling history was studied. High-speed imaging by means of a complementary metal-oxide-semiconductor image sensor camera allowed in situ measurement of the domain wall propagation speed under different poling conditions. The results also give evidence of the strong influence of the dielectric surface layer in this material. [ABSTRACT FROM AUTHOR]

As molecular spectroscopy makes its comeback to the limelight of fundamental sciences, scientists need ever better coherent light sources and diagnostic methods. Of particular importance for molecular spectroscopy is the mid infrared spectral region, where strong and narrow ro-vibrational excitations have their fundamental transition frequencies. Unfortunately, much technology in some portions of this spectral region is still rather pioneering. Here we present a high-resolution spectroscopy experiment, based on a molecular beam setup, which pushes the measured linewidth close to the transit time limit, on the order of 100 kHz. Moreover, we discuss the issue of frequency-noise characterization and the linewidth measurement of the ultrastable infrared laser used in the experiment. [ABSTRACT FROM AUTHOR]

We present a mid-IR high-precision spectrometer capable of performing accurate Doppler-free measurements with absolute calibration of the optical axis and high signal-to-noise ratio. The system is based on a widely tunable mid-IR offset-free frequency comb and a Quantum-Cascade-Laser (QCL). The QCL emission frequency is offset locked to one of the comb teeth to provide absolute-frequency calibration, spectral-narrowing, and accurate fine frequency tuning. Both the comb repetition frequency and QCL-comb offset frequency can be modulated to provide, respectively, slow- and fast-frequency-calibrated scanning capabilities. The characterisation of the spectrometer is demonstrated by recording sub-Doppler saturated absorption features of the CHF3 molecule at around 8.6 μm with a maximum signal-to-noise ratio of ∼7 × 103 in 10 s integration time, frequency-resolution of 160 kHz, and accuracy of less than 10 kHz. [ABSTRACT FROM AUTHOR]

Aims: Increasing age is the most important risk factor for atrial fibrillation (AF). Very high doses of exercise training might increase AF risk, while moderate levels seem to be protective. This study aimed to examine the effects of age on vulnerability to AF and whether long-term aerobic interval training (AIT) could modify these effects. Methods: Nine months old, male Sprague-Dawley rats were randomized to AIT for 16 weeks (old-ex) or to a sedentary control group (old-sed), and compared to young sedentary males (young-sed). After the intervention, animals underwent echocardiography, testing of exercise capacity (VO2max), and electrophysiology with AF induction before ex vivo electrophysiology. Fibrosis quantification, immunohistochemistry and western blotting of atrial tissue were performed. Results: Sustained AF was induced in vivo in 4 of 11 old-sed animals, but none of the old-ex or young-sed rats (p = 0.006). VO2max was lower in old-sed, while old-ex had comparable results to young-sed. Fibrosis was increased in old-sed (p = 0.006), with similar results in old-ex. There was a significantly slower atrial conduction in old-sed (p = 0.038), with an increase in old-ex (p = 0.027). Action potential duration was unaltered in old-sed, but prolonged in old-ex (p = 0.036). There were no differences in amount of atrial connexin 43 between groups, but a lateralization in atrial cardiomyocytes of old-sed, with similar findings in old-ex. Conclusion: AF vulnerability was higher in old-sed animals, associated with increased atrial fibrosis, lateralization of connexin-43, and reduced atrial conduction velocity. AIT reduced the age-associated susceptibility to AF, possibly through increased conduction velocity and prolongation of action potentials. [ABSTRACT FROM AUTHOR]

We provide an overview on terahertz (THz) frequency metrology, starting from the nowadays available continuous wave THz sources, discussing their main features such as tunability, spectral purity, and frequency referencing to the primary frequency standards. A comparison on the achieved results in high-precision molecular spectroscopy is given and discussed, and finally, a special emphasis poses on the future developments of this upcoming field. [ABSTRACT FROM AUTHOR]

Summary: Mainly driven by the recent dramatic progress of infrared technologies, as well as by the emerging methods for cooling of ground-state molecules, the field of precision molecular spectroscopy is experiencing a new youth, as it promises to lead major advances both in fundamental and applied science. The present review will encompass the main results obtained in the last two decades, by our group, in this scope, particularly in the mid infrared and THz spectral regions. Starting from the development of novel, metrological-grade coherent radiation sources, either in continuous-wave or in pulsed-emission regime, we will go through the realization of more an more sophisticated spectroscopic interrogation techniques. We will then conclude with the first demonstration of cavity-enhanced ro-vibrational spectroscopy on a buffer-gas-cooled molecular beam. From this brief overview it emerges that high-precision physical fundamental measurements can be done, at present, at an energy scale as low as the photons used for harnessing the molecular samples. [ABSTRACT FROM AUTHOR]

We report on the realization of a quartz-enhanced photoacoustic (QEPAS) sensor for measurement of HS gas traces. A distributed feedback diode laser working at 2.64 µm wavelength has been coupled to an acoustic detection module composed of a quartz tuning fork and a micro-resonator system, and the QEPAS signal has been optimized in terms of gas sample pressure and laser frequency modulation depth. The sensor shows a very good linearity with respect to the HS concentration. We performed an Allan-Werle variance analysis to investigate the sensor long-term stability, and we reached a detection limit of four parts per million for 1-s integration time and 500 parts per billion in 60-s integration time. The realized QEPAS sensor represents a good compromise between performance and handiness, in view of a fully portable device. [ABSTRACT FROM AUTHOR]

Aims Peripheral muscle dysfunction is a key mechanism contributing to exercise intolerance (i.e. breathlessness and fatigue) in heart failure patients with preserved ejection fraction ( HFpEF); however, the underlying molecular and cellular mechanisms remain unknown. We therefore used an animal model to elucidate potential molecular, mitochondrial, histological, and functional alterations induced by HFpEF in the diaphragm and soleus, while also determining the possible benefits associated with exercise training. Methods and results Female Dahl salt-sensitive rats were fed a low ( CON; n = 10) or high salt ( HFpEF; n = 11) diet of 0.3% or 8% NaCl, respectively, or a high salt diet in combination with treadmill exercise training ( n = 11). Compared with low-salt rats, high-salt rats developed ( P < 0.05) HFpEF. Compared with CON, the diaphragm of HFpEF rats demonstrated ( P < 0.05): a fibre type shift from fast-to-slow twitch; fibre atrophy; a decreased pro-oxidative but increased anti-oxidant capacity; reduced proteasome activation; impaired in situ mitochondrial respiration; and in vitro muscle weakness and increased fatigability. The soleus also demonstrated numerous alterations ( P < 0.05), including fibre atrophy, decreased anti-oxidant capacity, reduced mitochondrial density, and increased fatigability. Exercise training, however, prevented mitochondrial and functional impairments in both the diaphragm and soleus ( P < 0.05). Conclusion Our findings are the first to demonstrate that HFpEF induces significant molecular, mitochondrial, histological, and functional alterations in the diaphragm and soleus, which were attenuated by exercise training. These data therefore reveal novel mechanisms and potential therapeutic treatments of exercise intolerance in HFpEF. [ABSTRACT FROM AUTHOR]

We report on the evidence of saturation effects in a rotational transition of CH3OH around 2.5 THz, induced by a free-running continuous-wave quantum cascade laser (QCL). The QCL emission is used for direct-absorption spectroscopy experiments, allowing to study the dependence of the absorption coefficient on gas pressure and laser intensity. A saturation intensity of 25 μW/mm², for a gas pressure of 17 ibar, is measured. This result represents the initial step towards the implementation of a QCL-based high-resolution sub-Doppler THz spectroscopy, which is expected to improve by orders of magnitude the precision of THz spectrometers. [ABSTRACT FROM AUTHOR]

We report on a spectroscopic technique named intracavity quartz-enhanced photoacoustic spectroscopy (I-QEPAS) employed for sensitive trace-gas detection in the mid-infrared spectral region. It is based on a combination of QEPAS with a buildup optical cavity. The sensor includes a distributed feedback quantum cascade laser emitting at 4.33 μm. We achieved a laser optical power buildup factor of ~500, which corresponds to an intracavity laser power of ~0.75 W. CO2 has been selected as the target molecule for the I-QEPAS demonstration. We achieved a detection sensitivity of 300 parts per trillion for 4 s integration time, corresponding to a noise equivalent absorption coefficient of 1.4s10-8 cm-1 and a normalized noise-equivalent absorption of 3.2s10-10 W cm-1 Hz-1/2. [ABSTRACT FROM AUTHOR]

The use of a high-electron mobility semiconductor nanowire as transistor channel has recently allowed the extension of the spectral coverage of THz field-effect transistor detectors up to 1.5 THz. In this report, we demonstrate efficient operation of a field-effect transistor detector based on a semiconductor nanowire at a much higher frequency, 2.8 THz, with a responsivity ≈5V/W in a bandwidth ≈100 kHz, thus proving the full potential of such approach for the detection of THz quantum cascade lasers. Finally, such a THz sensing system is exploited to perform raster scan transmission imaging, with high spatial resolution, signal-to-noise ratio, and acquisition rate. [ABSTRACT FROM AUTHOR]

We investigate the performance of a surface-plasmon-resonance refractive-index (RI) sensor based on an optical resonator. The resonator transforms RI changes of liquid samples, interacting with the surface plasmon excited by near-infrared light, into a variation of the intra-cavity optical loss. Cavity ring-down measurements are provided as a proof of concept of RI sensing on calibrated mixtures. A characterization of the overall sensor response and noise features as well as a discussion on possible improvements is carried out. A reproducibility analysis shows that a resolution of 10−7–10−8 RIU is within reach over observation times of 1–30 s. The ultimate resolution is set only by intrinsic noise features of the cavity-based method, pointing to a potential limit below 10−10 RIU/√Hz. [ABSTRACT FROM AUTHOR]

We provide an overview of recent developments of quantum cascade lasers (QCLs), from the mid-infrared (mid-IR) to the far-IR (THz) range, with a special focus on their metrological-grade applications in a number of fields. A special emphasis on the physics of the QCLs allows underlining peculiar effects and device features recently unveiled that pave the way to novel demanding photonics applications. [ABSTRACT FROM AUTHOR]

We report on a passive ionizing radiation sensor based on a fiber-optic resonant cavity interrogated by a high resolution interferometric technique. After irradiation in clinical linear accelerators, we observe significant variations of the fiber thermo-optic coefficient. Exploiting this effect, we demonstrate an ultimate detection limit of 160 mGy with an interaction volume of only 6 × 10-4 mm3. Thanks to its reliability, compactness, and sensitivity at biomedical dose levels, our system lends itself to real applications in radiation therapy procedures as well as in radiation monitoring and protection in medicine, aerospace, and nuclear power plants. [ABSTRACT FROM AUTHOR]

Background: Although high aerobic capacity is associated with effective cardiac function, the effect of aerobic capacity on atrial function, especially in terms of cellular mechanisms, is not known. We aimed to investigate whether rats with low inborn maximal oxygen uptake (VO2 max) had impaired atrial myocyte contractile function when compared to rats with high inborn VO2 max. Methods and Results: Atrial myocyte function was depressed in Low Capacity Runners (LCR) relative to High Capacity Runners (HCR) which was associated with impaired Ca2+ handling. Fractional shortening was 52% lower at 2 Hz and 60% lower at 5 Hz stimulation while time to 50% relengthening was 43% prolonged and 55% prolonged, respectively. Differences in Ca2+ amplitude and diastolic Ca2+ level were observed at 5 Hz stimulation where Ca2+ amplitude was 70% lower and diastolic Ca2+ level was 11% higher in LCR rats. Prolonged time to 50% Ca2+ decay was associated with reduced sarcoplasmic reticulum (SR) Ca2+ ATPase function in LCR (39%). Na+/Ca2+ exchanger activity was comparable between the groups. Diastolic SR Ca2+ leak was increased by 109%. This could be partly explained by increased ryanodine receptors phosphorylation at the Ca2+-calmodulin-dependent protein kinase-II specific Ser-2814 site in LCR rats. T-tubules were present in 68% of HCR cells whereas only 33% LCR cells had these structures. In HCR, the significantly higher numbers of cells with T-tubules were combined with greater numbers of myocytes where Ca2+ release in the cell occurred simultaneously in central and peripheral regions, giving rise to faster and more spatial homogenous Ca2+-signal onset. Conclusion: This data demonstrates that contrasting for low or high aerobic capacity leads to diverse functional and structural remodelling of atrial myocytes, with impaired contractile function in LCR compared to HCR rats. [ABSTRACT FROM AUTHOR]

The first results of an optical method for measuring radiocarbon concentrations, based on mid-infrared laser spectroscopy of a carbon dioxide gas sample, are presented with the theoretical bases explained in detail. The first measurements on modern and highly enriched samples show the extreme linearity of this technique over more than 5 decades. An intercomparison with accelerator mass spectrometry (AMS) is performed both for modern and 14C-dead samples, assessing the almost perfect agreement of their respectively measured concentration values. The main features of our technique are compared with liquid scintillation counting (LSC) and AMS, and future developments of the current setup are discussed. [ABSTRACT FROM AUTHOR]

We present a narrow-linewidth, singly-resonant cw optical parametric oscillator, emitting more than 1 W in the 2.7–4.2 µm range. The OPO is pumped by a narrow linewidth (40 kHz) fibre-laser system and the signal frequency is locked to a high-finesse Fabry–Pérot cavity in order to increase the spectral resolution, thus obtaining a residual linewidth of 70 kHz for the signal. We tested the spectral performance of our OPO on several transitions in the ν1 rovibrational band of CH3I, measuring line intensities and showing sub-Doppler dip detection. [ABSTRACT FROM PUBLISHER]

In this paper, we analyze the sensitivity enhancement attainable by combining a wavelength modulation (WM) technique to integrated cavity output spectroscopy (ICOS), pointing out how the spectrometer's parameters and the acquisition strategy affect the detection noise in both techniques. We point out that WM-ICOS is mainly limited by the slow scan rate that it requires, compared to regular ICOS. Nevertheless, according to our analysis, WM can still appreciably improve the SNR of an ultrasensitive ICOS system, if the cavity transmission is so low that the detector noise is not negligible. In light of these considerations, we directly compare the performance of ICOS and WM-ICOS in a high sensitivity ambient-air methane detection experiment, finding a good agreement with the theoretical influence of the various spectrometer parameters. [ABSTRACT FROM AUTHOR]