Self referencing LED detection system for spectroscopy applications

Abstract

A light emitting diode (LED) based detection system is employed for spectroscopy based applications. LEDs are used as monochromatic light sources for applications at specific and pre-defined wavelengths. Spectrographic information is generated using LEDs of different wavelengths ranging from 260 nm to 1400 nm. Multiple wavelength information is generated by coupling light from each LED into an intensity and mode mixing fiber bundle. A dual beam approach of using a reference and a sample photodiode ensures automatic drift correction. Interference filters at the LED input fiber reduce the spectral bandwidth of the monochromatic light emission to a useful 10 nm bandwidth by cutting off the LEDs trailing emission distribution allowing for absorbance measurements similar to typical spectrometers.

Description

CROSS-REFERENCE TO RELATED APPLICATION[0001]This application claims the priority of U.S. Provisional Application No. 60 / 885,588 filed Jan. 20, 2007.BACKGROUND[0002]Absorption spectroscopy uses the range of electromagnetic spectra in which a substance absorbs. In absorption spectroscopy light of a particular wavelength is passed through the sample. After calibration, the amount of absorption can be related to the sample concentration through the Beer-Lambert law. Examples of absorption spectroscopy include, for example, ultraviolet / visible (UVNIS) absorption spectroscopy (most often performed on liquid samples to detect molecular content) and infrared (IR) spectroscopy (most often performed on liquid, semi-liquid (paste or grease), dried, or solid samples to determine molecular information, including structural information).[0003]Spectroscopic analysis typically uses a spectrometer. The spectrometer typically includes a radiation source such as a deuterium, tungsten or xenon lamp cap...

AI Technical Summary

Benefits of technology

[0007]A sample cell is connected to the detection system via the fiber optic output and the sample photodiode input. LEDs are switched on and off sequentially. Light output is measured simultaneously by the reference photodiode and the sample photodiode. Thus, dark, reference and sample intensity are detected simultaneously and any LED drift or stray light can be corrected for automatically, ensuring precise measurements and long-term drift stability. To reduce the spectral bandwidth of the LEDs, interference filters are either placed between the LED and the coupling fiber or are coated directly on the LED coupling fiber to optimize light throughput.

Problems solved by technology

While this equipment provides analysis flexibility, it also requires complicated and expensive light sources, gratings, monochromators and other components to take advantage of this flexibility.

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