Fourier transform spectrometer based on high-repetition-rate mid-infrared supercontinuum sources for trace gas detection.

We present a fast-scanning Fourier transform spectrometer (FTS) in combination with high-repetition-rate mid-infrared supercontinuum sources, covering a wavelength range of 2-10.5 µm. We demonstrate the performance of the spectrometer for trace gas detection and compare various detection methods: baseband detection with a single photodetector, baseband balanced detection, and synchronous demodulation at the repetition rate of the supercontinuum source. The FTS uses off-the-shelf optical components and provides a minimum spectral resolution of 750 MHz. It achieves a noise equivalent absorption sensitivity of ∼10-6 cm-1 Hz-1/2 per spectral element, by using a 31.2 m multipass absorption cell.

Mid-infrared dual-comb spectroscopy with absolute frequency calibration using a passive optical reference.

We demonstrate an absolute-frequency-calibrated mid-infrared dual-comb spectrometer by using a reference absorption cell. The source is based on a singly-resonant OPO containing two MgO:PPLN crystals in a common ring cavity, synchronously pumped by two mode-locked Yb-fiber lasers. The repetition-rate of the two pumps are stabilized while their offset frequencies and the OPO cavity length are not actively controlled. The reference spectrum is used to correct the frequency fluctuations in the sample spectrum providing a high-quality averaged spectrum with spectral resolution of 6 GHz and calibration precision of 120 MHz, without adding any complexity to the experimental setup or signal processing.

Mid-infrared supercontinuum-based Fourier transform spectroscopy for plasma analysis.

Broadband mid-infrared (MIR) spectroscopy is a well-established and valuable diagnostic technique for reactive plasmas. Plasmas are complex systems and consist of numerous (reactive) types of molecules; it is challenging to measure and control reaction specificity with a good sensitivity. Here, we demonstrate the first use of a novel MIR supercontinuum (SC) source for quantitative plasma spectroscopy. The SC source has a wide spectral coverage of 1300-2700 cm-1 (wavelength range 3.7-7.7 µm), thus enabling broadband multispecies detection. The high spatial coherence of the MIR SC source provides long interaction path lengths, thereby increasing the sensitivity for molecular species. The combination of such a SC source with a custom-built FTIR spectrometer (0.1 cm-1 spectral resolution) allows detection of various gases with high spectral resolution. We demonstrate its potential in plasma applications by accurate identification and quantification of a variety of reaction products (e.g. nitrogen oxides and carbon oxides) under low-pressure conditions, including the molecular species with overlapping absorbance features (e.g. acetone, acetaldehyde, formaldehyde, etc.).

Analysis of speech-based measures for detecting and monitoring Alzheimer's disease.

Automatic diagnosis of the Alzheimer's disease as well as monitoring of the diagnosed patients can make significant economic impact on societies. We investigated an automatic diagnosis approach through the use of speech based features. As opposed to standard tests, spontaneous conversations are carried and recorded with the subjects. Speech features could discriminate between healthy people and the patients with high reliability. Although the patients were in later stages of Alzheimer's disease, results indicate the potential of speech-based automated solutions for Alzheimer's disease diagnosis. Moreover, the data collection process employed here can be done inexpensively by call center agents in a real-life application. Thus, the investigated techniques hold the potential to significantly reduce the financial burden on governments and Alzheimer's patients.

Scleral ulceration caused by Cryptococcus albidus in a patient with acquired immune deficiency syndrome.

PURPOSE: To describe a case of a scleral ulceration caused by Cryptococcus albidus in a patient with acquired immune deficiency syndrome (AIDS). DESIGN: Interventional case report. A 16-year-old girl with AIDS was admitted to the hospital with a 1-week history of cough, fever, and sudden onset of a painless scleral lesion on her left eye. Culture of the lesion revealed the fungus Crypotococcus albidus. RESULTS: The patient was treated with topical amphotericin B and systemic itraconazole, and she recovered fully over 4 weeks without sequelae. CONCLUSION: Cryptococcus albidus rarely causes disease in humans. It should be considered as a potential cause of ocular and systemic disease in patients with AIDS.

Corneal surgery for severe phacoemulsification burns.

OBJECTIVE: To evaluate the outcome of corneal surgery for the treatment of severe corneal phacoemulsification burns. DESIGN: Interventional case series. PARTICIPANTS: Four patients with severe intraoperative phacoemulsification burns. INTERVENTION: One patient underwent penetrating keratoplasty and 3 underwent lamellar keratoplasties for the treatment of their corneal burns. MAIN OUTCOME MEASURES: Preoperative and postoperative visual acuities, preoperative and postoperative corneal topographies, and clinical observation. RESULTS: The visual acuity (VA) after the phacoemulsification burn was counting fingers in all patients. One patient had a penetrating keratoplasty, whereas the other 3 had lamellar grafts. After the corneal surgery, the corrected postoperative VA was 20/30 to 20/50 in all patients, with astigmatism ranging from 2.5 to 5.5 diopters. CONCLUSION: Severe phacoemulsification burns can be safely treated with corneal surgery, with acceptable postoperative visual acuities.