A photonic instrument is proposed to boost the resolution for ultraviolet/optical/infrared spectral analysis and spectral imaging allowing the detection of narrow (0.00007-to-0.07-picometer wavelength resolution range) optical spectral signatures of chemical elements in space and planetary atmospheres. The idea underlying the proposal is to exploit the advantageous spectral characteristics of whispering-gallery-mode (WGM) resonators to obtain spectral resolutions at least three orders of magnitude greater than those of optical spectrum analyzers now in use. Such high resolutions would enable measurement of spectral features that could not be resolved by prior instruments.

Figure 1. A Resolution Booster exploits the advantage of WGM resonators to increase spectral resolution at least three orders of magnitude.
Tunable single-mode WGM resonators would be incorporated into optical spectrum analyzers as shown in the block diagram in Figure 1. The center of the spectral window of the spectrum analyzer will be tuned to the carrier frequency of interest. The rough snapshot of the signal under study will be taken. After that, the WGM filter will be inserted in front of the spectrum analyzer. The internal scanning of the spectrum analyzer will be switched off, while the WGM filter will be scanned through the frequency window. The narrow-band spectral features of the signal will be resolved as the result. In particular, for the purpose of measuring abundances of selected isotopes (e.g., isotopes of carbon) in compounds in outer space and in atmospheres of Earth and other planets, an instrument equipped according to the proposal could measure narrow (width < 10 MHz) optical spectral signatures of compounds (e.g., CO2) containing such isotopes.

Figure 2. These Resonance Quality Factors (Q values) plotted versus wavelength were obtained from measurements on WGM resonators made of the indicated materials.
The advantageous spectral characteristics of WGM resonators include high resonance quality factors (see Figure 2) and clean spectra. In addition, relative to other tunable optical resonators that have similar free spectral ranges and Q values, tunable single-mode WGM resonators can be tuned over wider frequency bands and exhibit much greater rejection ratios. A tunable single-mode WGM resonator incorporated into a spectrum analyzer according to the proposal would have a power consumption of no more than a few milliwatts, would have a mass of about 100 g, would have no moving parts, and could be operated autonomously. In addition to being key components of contemplated new high-resolution optical spectrum analyzers, tunable single-mode WGM resonators could be retrofit to current optical spectrum analyzers to improve their performances.

This work was done by Anatoliy Savchenkov, Andrey Matsko, Dmitry Strekalov, and Lute Maleki of Caltech for NASA’s Jet Propulsion Laboratory.

In accordance with Public Law 96-517, the contractor has elected to retain title to this invention. Inquiries concerning rights for its commercial use should be addressed to:

Innovative Technology Assets Management
JPL
Mail Stop 202-233
4800 Oak Grove Drive
Pasadena, CA 91109-8099
(818) 354-2240
E-mail: This email address is being protected from spambots. You need JavaScript enabled to view it.

Refer to NPO-43993, volume and number of this NASA Tech Briefs issue, and the page number.

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Energy consumption Imaging and visualization Optics Physical Sciences
This Brief includes a Technical Support Package (TSP).
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Spectrum Analyzers Incorporating Tunable WGM Resonators

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This article first appeared in the April, 2009 issue of NASA Tech Briefs Magazine (Vol. 33 No. 4).

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Overview

The document presents a technical support package detailing a novel high-resolution chemical sensor based on whispering gallery modes (WGM) developed by the Quantum Sciences and Technology Group, led by researchers including Anatoliy Savchenkov, Andrey Matsko, and Lute Maleki. This innovative photonic instrument is designed for detecting narrow optical spectral signatures of chemical elements in planetary atmospheres, particularly for missions to Mars and the Orbiting Carbon Observatory (OCO).

The sensor boasts several key advantages: it operates with a resolution at least three orders of magnitude higher than existing optical spectrum analyzers, allowing for the precise identification of close spectral lines crucial for isotope characterization and atmospheric content analysis. The device is compact, weighing approximately 100 grams, consumes minimal power (a few milliwatts), and features no moving parts, enabling autonomous operation in space environments.

The importance of this technology lies in its ability to analyze isotopic ratios of elements such as hydrogen, carbon, and oxygen, which provide insights into planetary evolution and the history of atmospheres. For instance, the Mars Science Laboratory mission, which includes a gas chromatograph and mass spectrometer, aims to understand the Martian atmosphere and water history through the analysis of organic compounds and isotope ratios.

The document highlights the sensor's compatibility with existing spectrum analyzers, significantly enhancing their resolution without the need for extensive re-engineering. For example, it can improve the spectral resolution of the Fourier spectrometer used in the Mars Express mission by up to four orders of magnitude, from a resolution of 60 GHz to much finer distinctions.

In summary, this high-resolution chemical sensor represents a significant advancement in the field of planetary exploration, offering enhanced capabilities for analyzing atmospheric compositions and isotopic variations. Its development aligns with NASA's goals of improving the understanding of planetary atmospheres and supporting future missions aimed at exploring the chemical signatures of celestial bodies. The document serves as a resource for further information on the technology and its potential applications in aerospace and beyond.