Synchronous upconversion of quantum cascade lasers in AgGaS2.

We investigate synchronous upconversion of a pulsed, tunable quantum cascade laser (QCL) in the important 5.4-10.2 µm range, with a 30 kHz, Q-switched, 1064 nm laser. The possibility to accurately control the repetition rate and pulse duration of the QCL results in a good temporal overlap with the Q-switched laser, leading to an upconversion quantum efficiency of 16% in a 10 mm-long AgGaS2 crystal. We investigate the noise properties of the upconversion process in terms of pulse-to-pulse energy stability and timing jitter. For QCL pulses in the 30-70 ns range the upconverted pulse-to-pulse stability is approximately 1.75%. The demonstrated combination of broad tunability and high signal to noise in the system is well-suited for mid-IR spectral analysis of highly absorbing samples.

Lower or Higher Oxygenation Targets for Acute Hypoxemic Respiratory Failure.

BACKGROUND: Patients with acute hypoxemic respiratory failure in the intensive care unit (ICU) are treated with supplemental oxygen, but the benefits and harms of different oxygenation targets are unclear. We hypothesized that using a lower target for partial pressure of arterial oxygen (Pao2) would result in lower mortality than using a higher target. METHODS: In this multicenter trial, we randomly assigned 2928 adult patients who had recently been admitted to the ICU (≤12 hours before randomization) and who were receiving at least 10 liters of oxygen per minute in an open system or had a fraction of inspired oxygen of at least 0.50 in a closed system to receive oxygen therapy targeting a Pao2 of either 60 mm Hg (lower-oxygenation group) or 90 mm Hg (higher-oxygenation group) for a maximum of 90 days. The primary outcome was death within 90 days. RESULTS: At 90 days, 618 of 1441 patients (42.9%) in the lower-oxygenation group and 613 of 1447 patients (42.4%) in the higher-oxygenation group had died (adjusted risk ratio, 1.02; 95% confidence interval, 0.94 to 1.11; P = 0.64). At 90 days, there was no significant between-group difference in the percentage of days that patients were alive without life support or in the percentage of days they were alive after hospital discharge. The percentages of patients who had new episodes of shock, myocardial ischemia, ischemic stroke, or intestinal ischemia were similar in the two groups (P = 0.24). CONCLUSIONS: Among adult patients with acute hypoxemic respiratory failure in the ICU, a lower oxygenation target did not result in lower mortality than a higher target at 90 days. (Funded by the Innovation Fund Denmark and others; HOT-ICU ClinicalTrials.gov number, NCT03174002.).

Saturation Dependence of Flame Thermometry Using Mid-IR Degenerate Four Wave Mixing.

It has previously been demonstrated that the ratio of the degenerate four wave mixing signal from two hot water line groups near 3231 cm-1 can be used for seedless flame temperature measurements. This paper presents an investigation of the impact of saturation effects on the measured signal intensity from each line group, as well as an estimation of the accuracy of the method. The saturation effects observed here would result in a large systematic error if they are not taken into account when using the degenerate four-wave mixing intensity of these water line groups to calculate the flame temperature.

Infrared Degenerate Four-wave Mixing with Upconversion Detection for Quantitative Gas Sensing.

We present a protocol for performing gas spectroscopy using infrared degenerated four-wave mixing (IR-DFWM), for the quantitative detection of gas species in the ppm-to-single-percent range. The main purpose of the method is the spatially resolved detection of low-concentration species, which have no transitions in the visible or near-IR spectral range that could be used for detection. IR-DFWM is a nonintrusive method, which is a great advantage in combustion research, as inserting a probe into a flame can change it drastically. The IR-DFWM is combined with upconversion detection. This detection scheme uses sum-frequency generation to move the IR-DFWM signal from the mid-IR to the near-IR region, to take advantage of the superior noise characteristics of silicon-based detectors. This process also rejects most of the thermal background radiation. The focus of the protocol presented here is on the proper alignment of the IR-DFWM optics and on how to align an intracavity upconversion detection system.

Comparison of an InSb Detector and Upconversion Detector for Infrared Polarization Spectroscopy.

This paper compares the signal-to-noise ratio obtained using an InSb photodiode for infrared (IR) polarization spectroscopy to that obtained using an upconversion detector, and shows a factor 64 improvement by the change. Upconversion detection is based on using sum frequency generation to move the IR optical signal to near-visible wavelengths to improve the sensitivity.