High-resolution molecular fingerprinting in the 11.6-15†µm range by a quasi-CW difference-frequency-generation laser source.

We report an approach for high-resolution spectroscopy using a widely tunable laser emitting in the molecular fingerprint region. The laser is based on difference-frequency generation (DFG) in a nonlinear orientation-patterned GaAs crystal. The signal laser, a CO2 gas laser, is operated in a kHz-pulsed mode while the pump laser, an external-cavity quantum cascade laser, is finely mode-hop-free tuned. The idler radiation covers a spectral range of ∼11.6-15 µm with a laser linewidth of ∼ 2.3 MHz. We showcase the versatility and the potential for molecular fingerprinting of the developed DFG laser source by resolving the absorption features of a mixture of several species in the long-wavelength mid-infrared. Furthermore, exploiting the wide tunability and resolution of the spectrometer, we resolve the broadband absorption spectrum of ethylene (C2H4) over ∼13-14.2 µm and quantify the self-broadening coefficients of some selected spectral lines.

Femtosecond Mamyshev fiber oscillator started by a passively Q-switched microchip laser.

A femtosecond Mamyshev fiber oscillator in normal dispersion mode at 1 µm was started reliably and safely by an inexpensive diode-pumped passively Q-switched monolithic microchip laser emitting 300-ps pulses. Four-wave mixing spectral broadening is shown to play a pivotal role in starting the Mamyshev oscillator, owing to the random short and intense temporal fluctuations allowed by its ∼10-nm bandwidth. Systematic studies of the starting dynamics show that a success rate of 100% of the attempts is achieved with modest seed energy, as low as ∼30 nJ from the sub-nanosecond laser, corresponding to ∼100 pJ for the total four-wave mixing signal required to start the oscillation.

Feed-forward coherent link from a comb to a diode laser: Application to widely tunable cavity ring-down spectroscopy.

We apply a feed-forward frequency control scheme to establish a phase-coherent link from an optical frequency comb to a distributed feedback (DFB) diode laser: This allows us to exploit the full laser tuning range (up to 1 THz) with the linewidth and frequency accuracy of the comb modes. The approach relies on the combination of an RF single-sideband modulator (SSM) and of an electro-optical SSM, providing a correction bandwidth in excess of 10 MHz and a comb-referenced RF-driven agile tuning over several GHz. As a demonstration, we obtain a 0.3 THz cavity ring-down scan of the low-pressure methane absorption spectrum. The spectral resolution is 100 kHz, limited by the self-referenced comb, starting from a DFB diode linewidth of 3 MHz. To illustrate the spectral resolution, we obtain saturation dips for the 2ν3 R(6) methane multiplet at µbar pressure. Repeated measurements of the Lamb-dip positions provide a statistical uncertainty in the kHz range.

Feed-forward comb-assisted coherence transfer to a widely tunable DFB diode laser.

The transfer of phase coherence from an ultrastable master laser to a distributed feedback diode laser, using an optical comb as a transfer oscillator, is obtained via a new scheme allowing continuous scanning across the whole tuning range of the slave laser together with absolute frequency determination. This is accomplished without phase lock loops, through a robust high-bandwidth feed-forward control acting directly on the slave laser output radiation. The correction is obtained by means of a dual-parallel Mach-Zehnder interferometer used as an optical single-sideband modulator. Coherence transfer across a master-slave frequency gap of 14 THz yields an ∼10 kHz linewidth providing high injection efficiency of an optical cavity with finesse 250 000. This allows demonstrating a cavity ring-down absorption spectrum of low-pressure ambient air over a 300 GHz spectral window.

Conjugating precision and acquisition time in a Doppler broadening regime by interleaved frequency-agile rapid-scanning cavity ring-down spectroscopy.

We propose a novel approach to cavity-ring-down-spectroscopy (CRDS) in which spectra acquired with a frequency-agile rapid-scanning (FARS) scheme, i.e., with a laser sideband stepped across the modes of a high-finesse cavity, are interleaved with one another by a sub-millisecond readjustment of the cavity length. This brings to time acquisitions below 20 s for few-GHz-wide spectra composed of a very high number of spectral points, typically 3200. Thanks to the signal-to-noise ratio easily in excess of 10 000, each FARS-CRDS spectrum is shown to be sufficient to determine the line-centre frequency of a Doppler broadened line with a precision of 2 parts over 1011, thus very close to that of sub-Doppler regimes and in a few-seconds time scale. The referencing of the probe laser to a frequency comb provides absolute accuracy and long-term reproducibility to the spectrometer and makes it a powerful tool for precision spectroscopy and line-shape analysis. The experimental approach is discussed in detail together with experimental precision and accuracy tests on the (30 012) ← (00 001) P12e line of CO2 at ∼1.57 µm.

Endovascular Treatment of Popliteal Artery Aneurysms: A Word of Caution after Long-Term Follow-up.

BACKGROUND: The aim of this work was to evaluate the long-term patency of endografting in the treatment of popliteal artery aneurysms (PAAs) and to identify which factors may be predictors of graft occlusion. METHODS: All the patients who underwent endovascular repair of PAA were analyzed from 2006 until 2014 on the basis of symptoms, comorbidities, limb salvage, and long-term patency. The predictive value of the different variables was assessed in univariate analysis for primary patency and, for factors resulted significant, a multivariate analysis was performed. The Kaplan-Meier life table method was used to calculate patency and limb salvage. RESULTS: We treated 65 PAAs in 57 patients (53 men and 4 women). PAAs were symptomatic in 26 cases (40%) and 34% were the emergency cases; the mean aneurysm size was 33.8 ± 17 mm. Mean follow-up was 35 months ± 25. Graft occlusion occurred in 22 limbs (35%). We had 9 amputations (14.5%). The late conversion to open surgery was 6.4%. The cumulative estimated 60-month primary patency, secondary patency, and limb salvage were respectively 57% (standard error [SE] ±0.7), 73% (SE ±0.7), and 83% (SE ±0.5). We found that diabetes (hazard ratio [HR] 2.936, 95% confidence interval [CI] 0.993-8.683), associated percutaneous transluminal angioplasty (PTA) procedures (HR 2.534, 95% CI 1.115-5.757), symptoms (HR 2.492, 95% CI 1.127-5.510), and runoff scores (HR 2.069, 95% CI 0.942-4.544) were the most important risk factors for long-term patency at univariate analysis. When considering a multivariate analysis symptoms (HR 2.066, 95% CI 0.862-4.952) become the principal risk factor followed by diabetes (HR 1.808, 95% CI 0.531-6.157)], runoff scores (HR 1.716, 95% CI 0.757-3.893) and associated PTA procedures (HR 1.441, 95% CI 0.519-3.839), but no one reached a statistical significance. CONCLUSIONS: On the base of our experience it seems that several factors affect durability in PAA endovascular repair, especially the presence of acute symptoms, diabetes, and runoff. Therefore until further refined clinical studies, we believe that the actual role of this technique must be yet clarified.

Wide-bandwidth Pound-Drever-Hall locking through a single-sideband modulator.

An integrated single-sideband modulator is used as the sole wide-bandwidth frequency actuator in a Pound-Drever-Hall locking loop. Thanks to the large modulation bandwidth, the device enables a locking range of ±75 MHz and a control bandwidth of 5 MHz without the need for a second feedback loop. As applied to the coupling of an extended-cavity diode laser at 1.55 µm to a high-finesse optical cavity, the in-loop frequency noise spectral density reaches a minimum of 1 mHz/Hz(1/2) at 1 kHz.

Comb-locked cavity ring-down spectrometer.

Extreme frequency accuracy and high sensitivity are obtained with a novel comb-locked cavity-ring-down spectrometer operating in the near-infrared from 1.5 to 1.63 µm. A key feature of our approach is the tight frequency locking of the probe laser to the comb, ensuring very high reproducibility and accuracy to the frequency axis upon scanning the comb repetition rate, as well as an efficient light injection into a length-swept high-finesse passive cavity containing the gas sample. Spectroscopic tests on the (30012) ← (00001) P14e line of CO2 at ∼1.57 µm demonstrate an accuracy of ∼17 kHz on the line center frequency in a Doppler broadening regime over the time scale of about 5 min, corresponding to four consecutive spectral scans of the absorption line. Over a single scan, which consists of 1500 spectral points over 75 s, the limit of detection is as low as 5.7 × 10(-11) cm(-1).

Printing MEMS: Application of Inkjet Techniques to the Manufacturing of Inertial Accelerometers.

In the last few years, the manufacturing of microelectromechanical systems (MEMS) by means of innovative tridimensional and bidimensional printing technologies has significantly catalyzed the attention of researchers. Inkjet material deposition, in particular, can become a key enabling technology for the production of polymer-based inertial sensors characterized by low cost, high manufacturing scalability and superior sensitivity. In this paper, a fully inkjet-printed polymeric accelerometer is proposed, and its manufacturing steps are described. The manufacturing challenges connected with the inkjet deposition of SU-8 as a structural material are identified and addressed, resulting in the production of a functional spring-mass sensor. A step-crosslinking process allows optimization of the final shape of the device and limits defects typical of inkjet printing. The resulting device is characterized from a morphological point of view, and its functionality is assessed in performing optical readout. The acceleration range of the optimized device is 0-0.7 g, its resolution is 2 × 10-3 g and its sensitivity is 6745 nm/g. In general, the work demonstrates the feasibility of polymeric accelerometer production via inkjet printing, and these characteristic parameters demonstrate their potential applicability in a broad range of uses requiring highly accurate acceleration measurements over small displacements.

Comb-locked frequency-swept synthesizer for high precision broadband spectroscopy.

Frequency combs have made optical metrology accessible to hundreds of laboratories worldwide and they have set new benchmarks in multi-species trace gas sensing for environmental, industrial and medical applications. However, current comb spectrometers privilege either frequency precision and sensitivity through interposition of a cw probe laser with limited tuning range, or spectral coverage and measurement time using the comb itself as an ultra-broadband probe. We overcome this restriction by introducing a comb-locked frequency-swept optical synthesizer that allows a continuous-wave laser to be swept in seconds over spectral ranges of several terahertz while remaining phase locked to an underlying frequency comb. This offers a unique degree of versatility, as the synthesizer can be either repeatedly scanned over a single absorption line to achieve ultimate precision and sensitivity, or swept in seconds over an entire rovibrational band to capture multiple species. The spectrometer enables us to determine line center frequencies with an absolute uncertainty of 30 kHz and at the same time to collect absorption spectra over more than 3 THz with state-of-the-art sensitivity of a few 10-10 cm-1. Beyond precision broadband spectroscopy, the proposed synthesizer is an extremely promising tool to force a breakthrough in terahertz metrology and coherent laser ranging.

Tension hemothorax due to iatrogenic subclavian artery perforation: Hybrid management of a very rare complication.

BACKGROUND: Tension hemothorax is a rare event, due to different causes: trauma, ruptured thoracic aorta aneurysms, or as a complication of central venous line placement due to inadvertent artery puncture or cannulation. Tension hemothorax leads to both hypovolemic and obstructive shock and can require emergency management. PRESENTATION OF CASE: A 63 years old lady underwent a complicated surgical procedure for a postoperative small bowel obstruction after radical cystectomy. During the procedure, a central venous catheter was placed, under ultrasound guidance, in the right jugular vein but an unknown puncture of the right subclavian artery occurred. In the early phase of the postoperative course, a hypovolemic/obstructive shock developed because of a tension hemothorax. The patient underwent an emergency thoracotomy in the hybrid room, followed by an endovascular repair of the arterial laceration. A recurrent hemothorax developed a few hours later because of an endoleak that was treated successfully with a second endovascular approach and a balloon dilatation of the stent. CONCLUSIONS: tension hemothorax due to inadvertent subclavian artery laceration can be life-threatening and should be managed in a hybrid room with endovascular and surgical capabilities.

Comb-locked Lamb-dip spectrometer.

Overcoming the Doppler broadening limit is a cornerstone of precision spectroscopy. Nevertheless, the achievement of a Doppler-free regime is severely hampered by the need of high field intensities to saturate absorption transitions and of a high signal-to-noise ratio to detect tiny Lamb-dip features. Here we present a novel comb-assisted spectrometer ensuring over a broad range from 1.5 to 1.63 µm intra-cavity field enhancement up to 1.5 kW/cm(2), which is suitable for saturation of transitions with extremely weak electric dipole moments. Referencing to an optical frequency comb allows the spectrometer to operate with kHz-level frequency accuracy, while an extremely tight locking of the probe laser to the enhancement cavity enables a 10(-11) cm(-1) absorption sensitivity to be reached over 200 s in a purely dc direct-detection-mode at the cavity output. The particularly simple and robust detection and operating scheme, together with the wide tunability available, makes the system suitable to explore thousands of lines of several molecules never observed so far in a Doppler-free regime. As a demonstration, Lamb-dip spectroscopy is performed on the P(15) line of the 01120-00000 band of acetylene, featuring a line-strength below 10(-23) cm/mol and an Einstein coefficient of 5 mHz, among the weakest ever observed.

Sac enlargement due to seroma after endovascular abdominal aortic aneurysm repair with the Endologix PowerLink device.

A patient who had undergone endovascular repair of an abdominal aortic aneurysm with the Endologix PowerLink bifurcated system presented with delayed aortic aneurysm enlargement due to assumed endotension. He was treated with aortic sac evacuation and wrapping of the endograft. This is the first report of endotension and aneurysm sac enlargement after implantation of the PowerLink endograft.