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A dual Fabry-Perot cavity for fast assessments of gasnumber density
Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
(Engelska)Manuskript (preprint) (Övrigt vetenskapligt)
Nationell ämneskategori
Atom- och molekylfysik och optik
Identifikatorer
URN: urn:nbn:se:umu:diva-110276OAI: oai:DiVA.org:umu-110276DiVA, id: diva2:861914
Tillgänglig från: 2015-10-19 Skapad: 2015-10-19 Senast uppdaterad: 2018-06-07
Ingår i avhandling
1. Cavity enhanced optical sensing
Öppna denna publikation i ny flik eller fönster >>Cavity enhanced optical sensing
2015 (Engelska)Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
Alternativ titel[sv]
Kavitetsförstärkt optisk detektion
Abstract [en]

An optical cavity comprises a set of mirrors between which light can be reflected a number of times. The selectivity and stability of optical cavities make them extremely useful as frequency references or discri­mi­nators. With light coupled into the cavity, a sample placed inside a cavity will experience a significantly increased interaction length. Hence, they can be used also as amplifiers for sensing purposes. In the field of laser spectroscopy, some of the most sensitive techniques are therefore built upon optical cavities. In this work optical cavities are used to measure properties of gas samples, i.e. absorption, dispersion, and refractivity, with unprecedented precision.

The most sensitive detection technique of all, Doppler-broadened noise-immune cavity enhanced optical heterodyne molecular spectrometry (Db NICE-OHMS), has in this work been developed to an ultra-sensitive spectroscopic technique with unprecedented detection sensitivity. By identifying limiting factors, realizing new experimental setups, and deter­mining optimal detection conditions, the sensitivity of the technique has been improved several orders of magnitude, from 8 × 10-11 to 9 × 10-14 cm-1. The pressure interval in which NICE-OHMS can be applied has been extended by deri­vation and verification of dispersions equations for so-called Dicke narrowing and speed dependent broadening effects. The theoretical description of NICE-OHMS has been expanded through the development of a formalism that can be applied to the situations when the cavity absorption cannot be considered to be small, which has expanded the dynamic range of the technique. In order to enable analysis of a large number of molecules at their most sensitive transitions (mainly their funda­mental CH vibrational transitions) NICE-OHMS instrumentation has also been developed for measurements in the mid-infrared (MIR) region. While it has been difficult to realize this in the past due to a lack of optical modulators in the MIR range, the system has been based on an optical para­metric oscillator, which can be modulated in the near-infrared (NIR) range.

As the index of refraction can be related to density, it is possible to retrieve gas density from measurements of the index of refraction. Two such instru­men­tations have been realized. The first one is based on a laser locked to a measure­ment cavity whose frequency is measured by compassion with an optical frequency comb. The second one is based on two lasers locked to a dual-cavity (i.e. one reference and one measurement cavity). By these methods changes in gas density down to 1 × 10-9 kg/m3 can be detected.

All instrumentations presented in this work have pushed forward the limits of what previously has been considered measurable. The knowledge acquired will be of great use for future ultrasensitive cavity-based detection methods.

Ort, förlag, år, upplaga, sidor
Umeå: Umeå universitet, 2015. s. 124
Nyckelord
Optical resonators, Fiber Laser, Parametric oscillators, Optical frequency comb, Infrared, Spectroscopy heterodyne, Spectroscopy molecular, Absorption, Dispersion, Lineshapes, Optical standards and testing, Refractivety measurements
Nationell ämneskategori
Atom- och molekylfysik och optik
Identifikatorer
urn:nbn:se:umu:diva-110278 (URN)978-91-7601-338-0 (ISBN)
Disputation
2015-11-13, KBC-huset, KB3A9 (lilla hörsalen i KBC-huset), Umeå universitet, Umeå, 10:00 (Engelska)
Opponent
Handledare
Forskningsfinansiär
VetenskapsrådetKempestiftelserna
Tillgänglig från: 2015-10-23 Skapad: 2015-10-19 Senast uppdaterad: 2018-06-07Bibliografiskt granskad

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Silander, IsakHausmaninger, ThomasZelan, MartinFoltynowicz, Aleksandra

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