Abstract

Current infrared instrumentation permits the measurement of low concentrations or small quantities of material by electronic amplification of the signal and/or by utilizing infrared microscopes, beam condensers, and micro cells. It is now possible to achieve further sensitivity than permitted by these techniques. Using a computer of average transients (CAT) in conjunction with the spectrophotometer, a signal masked by noise can be increased with respect to the noise by a summation or averaging technique. In this method a region of the spectrum is scanned repetitively and the recorder input signal of each scan fed to the computer. A trigger circuit is utilized to synchronize the instrument and computer scans and provide a reference signal to the computer. The portion of the recorder input signal due to sample absorption is phase-locked to the reference signal, while the random component due to noise is not. When a number of input signals are added together, the phase-locked portions of the signal add arithmetically while the random noise adds out of phase and, therefore, tends to average out to zero. The improvement in the signal-to-noise ratio is proportional to the √N, where N is the number of scans summed. This technique has been applied recently to enhance the sensitivity of nuclear magnetic resonance and election spin resonance measurements <i>(1)</i>.

Infrared measurements of increased CF₂Cl₂ (CFC-12) absorption above the South Pole

Curtis P. Rinsland, Aaron Goldman, Frank J. Murcray, Frank H. Murcray, David G. Murcray, and Joel S. Levine
Appl. Opt. 27(3) 627-630 (1988)

Sensitivity analysis of differential absorption lidar measurements in the mid-infrared region

Paolo Francesco Ambrico, Aldo Amodeo, Paolo Di Girolamo, and Nicola Spinelli
Appl. Opt. 39(36) 6847-6865 (2000)

Evaluation of a linear birefringence measurement method with increased sensitivity

Marzena Prętka, Władysław A. Woźniak, Piotr Kurzynowski, and Sławomir Drobczyński
Appl. Opt. 55(4) 868-872 (2016)

High-sensitivity laser absorption measurements of broadband absorbers in the near-infrared spectral region

Kevin L. McNesby, Richard T. Wainner, Robert G. Daniel, Andrzej W. Miziolek, William M. Jackson, and Ian A. McLaren
Appl. Opt. 39(27) 5006-5011 (2000)

Increased mid-infrared supercontinuum bandwidth and average power by tapering large-mode-area chalcogenide photonic crystal fibers

Christian Rosenberg Petersen, Rasmus D. Engelsholm, Christos Markos, Laurent Brilland, Céline Caillaud, Johann Trolès, and Ole Bang
Opt. Express 25(13) 15336-15348 (2017)