Orientadores: Flávio Caldas da Cruz, Paulo Clóvis Dainese Júnior / Dissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Física Gleb Wataghin / Made available in DSpace on 2018-08-28T22:50:49Z (GMT). No. of bitstreams: 1 SaquinaulaBrito_JoseLuis_M.pdf: 4387885 bytes, checksum: 7b7c41672acbabf5abc5b7c398df00c0 (MD5) Previous issue date: 2015 / Resumo: Nos últimos 15 anos os pentes de frequências ópticas baseados em lasers de femtossegundos representaram uma revolução na área de metrología e medidas de precisão, permitindo medir diretamente frequências de várias centenas de THz assim como posibilitando o advento de relógios atômicos ópticos. Estes pentes também têm encontrado importantes aplicações em outras áreas da Física, tais como espectroscopia de alta resolução e precisão, geração de altos harmônicos na região da ultravioleta e raios X moles, ou até na procura de exoplanetas através da calibração de espectrômetros astrofísicos. Neste trabalho, estudamos a geração de pentes de frequências ópticas baseados em moduladores eletro-ópticos e fibras altamente não lineares, com o objetivo de implementar novas configurações, alternativas aos pentes baseados em lasers de femtossegundos. Um objetivo é implementar pentes com a maior largura de banda possível que ao mesmo tempo preservem alta coerência entre as frequências geradas, aproveitando componentes comercialmente disponíveis, desenvolvidos para comunicações ópticas na região espectral de 1550 nm. Buscamos implementar dois tipos de pentes de frequências ópticas. Um deles usa um modulador eletro-óptico e gera um pente com pequena largura de banda (10 nm) e espaçamento entre frequências de 25 GHz. O outro pente, gerado com base em fenômenos não lineares em fibras ópticas, fornece maior largura de banda (270 nm) com espaçamento entre frequências de 776 GHz. No caso do pente de frequências gerado pelo modulador (pente eletro-óptico), o processo é devido ao fenômeno eletro-óptico (efeito Pockels) dentro de um cristal de Niobato de Lítio que também forma uma cavidade óptica ressonante. Utilizamos um laser semicondutor contínuo e de frequência única em 1550 nm para gerar um pente (eletro-óptico) com largura espectral de 10 nm com espaçamento de 25 GHz entre as frequências. O outro pente de frequências ópticas é baseado na criação em cascata de produtos da mistura de quatro ondas produzidos a partir de dois lasers semicondutores contínuos, que foram utilizados tanto em onda contínua (cw) ou pulsados, i.e., com modulação de amplitude. Obtivemos espectros com largura de 269 nm (1431 nm ¿ 1700 nm) e espaçamento entre linhas de 6.3 nm (776 GHz). Finalmente, foi alargado o espectro do pente de frequências ópticas gerado pelo modulador eletro-óptico ao usar fibras altamente não lineares. O espectro obtido apresentaram um alargamento modesto, com largura de 23 nm e separação de 25 GHz entre as frequências / Abstract: In the last 15 years, optical frequency combs based on femtosecond lasers have represented a revolution in the area of metrology and precision measurements, making it possible to directly measure frequencies of several hundred terahertz, and affording the advent of optical atomic clocks. These frequency combs today are used in important applications in other areas of Physics, such as high resolution and accuracy spectroscopy, generation of high harmonics in the ultraviolet and soft X-rays region, or even in the search of exoplanets through calibration of Astrophysics spectrometers. In this work, we study the generation of optical frequency combs based on electro-optic modulators and highly nonlinear fibers, with the goal of implementing new configurations, which can be alternative to frequency combs based on femtosecond lasers. One particular goal is to implement frequency combs with the largest possible bandwidth, while still preserving the coherence between the generated frequencies, and taking advantage of commercially available components developed for optical communications, in the 1550 nm spectral region. We were interested in implement two types of optical frequency combs. One of them uses an electro-optical modulator and generates a frequency comb with small bandwidth (10 nm) and 25 GHz frequency spacing. The other comb, generated by nonlinear phenomena in optical fibers, provides greater bandwidth (270 nm) with a frequency spacing of 776 GHz. In the case of the frequency comb generated by the modulator (electro-optical comb), the process is due to the electro-optical phenomenon (Pockels effect) within a Lithium Niobate crystal which also forms a resonant optical cavity. We use a continuous-wave, single frequency semiconductor laser at 1550 nm to generate a frequency comb with a spectral width of 10 nm and 25 GHz frequency spacing. The other optical frequency comb is based on the creation of cascaded four-wave mixing products, produced from two continuous semiconductor lasers that were used both in continuous-wave (cw) or pulsed operation, i.e., with amplitude modulation.We obtained spectra with a width of 269 nm (1431 nm - 1700 nm) and line spacing of 6.3 nm (776 GHz). Finally, we combined both combs by using the highly nonlinear fiber to expand the optical comb spectrum generated by the electro-optical modulator. The resulting spectra showed a modest broadening, with a width of 23 nm and 25 GHz separation between frequencies / Mestrado / Física / Mestre em Física / 1186840 / 134295/2013-7 / CAPES / CNPQ

<p>Kerr frequency comb, a sequence of equally spaced sharp lines in frequency domain generated via four-wave mixing process, has multiple applications such as spectroscopy, metrology, and atomic clocks. Conventional frequency combs generated from mode-locked laser have the limitations of low repetition rate and large volume. One novel platform, silicon nitride (SiN) microring resonator (MRR), can overcome such disadvantages. The SiN MRR is a low loss waveguide resonator and has good reliability and capacity for on-chip integration, which enables a portable solution for Kerr frequency comb.</p><p>This thesis focuses on the design and characterization of the SiN MRR to optimize the important performance characteristics for the applications.<br></p><p>In Kerr comb applications, phase coherence between the comb lines is required to eliminate unwanted signals in the systems. Therefore, the investigation of the coherent state in MRR based comb generation can benefit the development of comb generation techniques. In particular, dark pulses exhibit much higher comb conversion efficiency than the single soliton combs.<br></p><p>The tunability of Kerr comb is another important performance characteristic of the applications, which is useful for multiple applications, such as matching the comb line spacing to the wavelength multiplexing grid for coherent communication or aligning the on-chip laser wavelength and MRR resonance frequency during the integration. The theoretic analysis of thermal tuning and experimental characterization of resonance frequency tuning via an on-chip microheater are performed in this thesis to explore the thermal tuning efficiency and its limitation.<br></p><p>Another important performance characteristics of the frequency comb is the comb bandwidth. Large bandwidth comb will be beneficial for application like dual comb spectroscopy. In addition, octave-spanning Kerr comb is desired due to its capacity of f-2f self-referencing for comb line frequencies stabilization for the applications like atomic clocks. To demonstrate on-chip octave-spanning Kerr soliton, the dispersion engineering is utilized in the device design to optimize the pump dispersion and dispersive wave generation simultaneously. The octave-spanning solitons are achieved on SiN MRRs with around 900 GHz repetition rate.<br></p><p>Finally, two optical division approaches are demonstrated to read out the large repetition rate of the octave-spanning soliton on all-SiN platform with auxiliary combs to enable the locking of undetectable repetition rate with less complexity in the fabrication and integration. The first approach uses a 25 GHz soliton; whose repetition rate is directly detectable via a photodiode. The second approach employs a Vernier scheme with an 880 GHz soliton to provide an alternative optical division scheme with lower requirements in fabrication ultrahigh Q MRRs. The divided repetition rate can be locked to enable the fully stabilization of frequency comb to provide an on-chip high stability and low noise frequency comb source.<br></p><p></p>

<p>In this Thesis I report on my work done in replicating the Pound-Drever-Hall (PDH) laser stabilization technique as well as applications of PDH to microring resonators and generated Optical Frequency Combs (OFC). These works have been broken down into three sections. First, I replicated the PDH method with a continuous wave (CW) laser along with a Fabry-Pérot Cavity (FPC). Second, I applied the same technique to a 25 GHz Free Spectral Range (FSR) microring resonator fabricated in Silicon Nitride. Third, I applied the PDH technique to a high Quality Factor (Q) high Free Spectral Range (FSR) microring resonator in preparation to lock the repetition rate of two soliton combs beat together. The last experiment was for an application towards a compact optical clock system; such systems will have a wide impact on the infrastructure of our navigation and communication structures in use today.</p>

This dissertation details work on high repetition rate semiconductor mode-locked lasers. The qualities of stable pulse trains and stable optical frequency content are the focus of the work performed. First, applications of such lasers are reviewed with particular attention to applications only realizable with laser performance such as presented in this dissertation. Sources of timing jitter are also reviewed, as are techniques by which the timing jitter of a 10 GHz optical pulse train may be measured. Experimental results begin with an exploration of the consequences on the timing and amplitude jitter of the phase noise of an RF source used for mode-locking. These results lead to an ultralow timing jitter source, with 30 fs of timing jitter (1 Hz to 5 GHz, extrapolated). The focus of the work then shifts to generating a stabilized optical frequency comb. The first technique to generating the frequency comb is through optical injection. It is shown that not only can injection locking stabilize a mode-locked laser to the injection seed, but linewidth narrowing, timing jitter reduction and suppression of superfluous optical supermodes of a harmonically mode-locked laser also result. A scheme by which optical injection locking can be maintained long term is also proposed. Results on using an intracavity etalon for supermode suppression and optical frequency stabilization then follow. An etalon-based actively mode-locked laser is shown to have a timing jitter of only 20 fs (1Hz-5 GHz, extrapolated), optical linewidths below 10 kHz and optical frequency instabilities less than 400 kHz. By adding dispersion compensating fiber, the optical spectrum was broadened to 2 THz and 800 fs duration pulses were obtained. By using the etalon-based actively mode-locked laser as a basis, a completely self-contained frequency stabilized coupled optoelectronic oscillator was built and characterized. By simultaneously stabilizing the optical frequencies and the pulse repetition rate to the etalon, a 10 GHz comb source centered at 1550 nm was realized. This system maintains the high quality performance of the actively mode-locked laser while significantly reducing the size weight and power consumption of the system. This system also has the potential for outperforming the actively mode-locked laser by increasing the finesse and stability of the intracavity etalon. The final chapter of this dissertation outlines the future work on the etalon-based coupled optoelectronic oscillator, including the incorporation of a higher finesse, more stable etalon and active phase noise suppression of the RF signal. Two appendices give details on phase noise measurements that incorporate carrier suppression and the noise model for the coupled optoelectronic oscillator.

La spectroscopie par transformation de Fourier par peignes de fréquences femtosecondes tire parti d’un interféromètre sans partie mobile. Il mesure les interférences entre deux peignes de fréquences, sources lasers à large bande spectrale constituée de raies fines et équidistantes. Il améliore significativement le temps de mesure et la limite de résolution spectrale des spectromètres de Fourier. Néanmoins, les conditions sur la stabilité à court terme des peignes ne peuvent pas être remplies par les techniques d’asservissement classique. Jusqu’à présent, aucun spectre de qualité n’a pu être mesuré avec un très faible temps d’acquisition. Cette thèse présente le développement d’une méthode de correction en temps réel capable de compenser les fluctuations résiduelles des peignes et de restituer des spectres sans artefacts. La méthode, analogique, ne nécessite aucun asservissement ou traitement informatique a posteriori. Ses performances sont démontrées dans le proche infrarouge (1,5 µm) et le visible (520 nm), à l’aide d’oscillateurs femtosecondes fibrés. Des spectres moléculaires couvrant 12 THz sont mesurés en 500 µs à limite de résolution Doppler. Ils sont en excellent accord avec les données de la littérature. Pour la première fois, le plein potentiel de la spectroscopie de Fourier par peignes de fréquences est démontré. Le domaine de l’infrarouge moyen est la région de prédilection de la spectroscopie moléculaire car la plupart des molécules y présentent des absorptions fortes et caractéristiques. Étendre la spectroscopie par peignes de fréquences à cette région est donc l’objectif suivant à atteindre. Dans cette optique, un peigne émettant autour de 3 µm est caractérisé. Il est basé sur la conversion non-linéaire par différence de fréquences d’un oscillateur à erbium élargi spectralement par une fibre fortement non-linéaire. / Dual-comb Fourier-transform spectroscopy takes advantage of an interferometer without moving parts. Interferences pattern between two femtosecond frequency combs, broadband laser sources whose spectra consist of evenly-spaced narrow lines, is measured. The measurement time and the spectral resolution are significantly improved compared to traditional Fourier spectrometers. However, the required short-term stability of the combs cannot be achieved by classic locking methods. Until now, no high-quality spectra could be recorded within a very short acquisition time. This thesis reports on the development of a real-time correction method able to compensate for the combs’ residual fluctuations and to restore non-distorted spectra. This analog technique does not require any locking system or a posteriori calculation. Its performance is demonstrated in the near-infrared (1.5 µm) and in the visible (520 nm) with fiber-based femtosecond lasers. Doppler-limited molecular spectra spanning 12 THz are measured within 500 µs. They are in excellent agreement with databases. For the first time, the full potential of dual-comb spectroscopy is demonstrated. The mid-infrared region is an attractive spectral range for molecular spectroscopy due to the molecules’ strong and characteristic absorptions. Therefore, extending dual-comb spectroscopy to this region is the next goal to achieve. Toward this goal, a comb emitting around 3 µm is characterized. It is based on the non-linear difference frequency generation from an erbium oscillator spectrally broadened with a highly non-linear fiber.

Doctor of Philosophy / Department of Physics / Kristan L. Corwin / We have made significant accomplishments in the development of portable frequency standard inside hollow optical fibers. Such standards will improve portable optical frequency references available to the telecommunications industry. Our approach relies on the development of a stabilized Cr:forsterite laser to generate the frequency comb in the near-IR region. This laser is self referenced and locked to a CW laser which in turn is stabilized to a sub-Doppler feature of a molecular transition. The molecular transition is realized using a hollow core fiber filled with acetylene gas. We finally measured the absolute frequency of these molecular transitions to characterize the references. In this thesis, the major ideas, techniques and experimental results for the development and absolute frequency measurement of the portable frequency references are presented. A prism-based Cr:forsterite frequency comb is stabilized. We have effectively used the prism modulation along with power modulation inside the cavity in order to actively stabilize the frequency comb. We have also studied the carrier-envelope-offset frequency (f0) dynamics of the laser and its effect on laser stabilization. A reduction of f0 linewidth from [similar to]2 MHz to [similar to]20 kHz has also been observed. Both our in-loop and out-of-loop measurements of the comb stability showed that the comb is stable within a part in 10^11 at 1-s gate time and is currently limited by our reference signal. In order to develop this portable frequency standard, saturated absorption spectroscopy is performed on the acetylene v1+v3 band near 1532 nm inside different kinds of hollow optical fibers. The observed linewidths are a factor 2 narrower in the 20 um fiber as compared to 10 um fiber, and vary from 20-40 MHz depending on pressure and power. The 70 um kagome fiber shows a further reduction in linewidth to less than 10 MHz. In order to seal the gas inside the hollow optical fiber, we have also developed a technique of splicing the hollow fiber to solid fiber in a standard commercial arc splicer, rather than the more expensive filament splicer, and achieved comparable splice loss. We locked a CW laser to the saturated absorption feature using a Frequency Modulation technique and then compared to an optical frequency comb. The stabilized frequency comb, providing a dense grid of reference frequencies in near-infrared region is used to characterize and measure the absolute frequency reference based on these hollow optical fibers.

The global traffic is experiencing an exponential growth posing severe challenges to the communication networks in terms of capacity. As a future-proof technology fiber communication is widely implemented in different network segments, which can be categorized by transmission distance as long-haul and short-reach. This thesis focuses on the short-reach communication networks including fiber access network connecting the end users to the metro/core networks that covering tens of kilometers and optical datacenter network handling the traffic within the datacenter with distance up to a few kilometers. For fiber access networks, wavelength division multiplexing passive optical networks (WDM-PONs) assign a dedicated wavelength channel to each user guaranteeing high data rate. Dense channels enlarges the user count but makes the signals vulnerable to the wavelength drift. In this regard we propose two schemes based on optical frequency comb technique to generate stable carriers for WDM-PONs. Meanwhile, radio-over-fiber techniques allows the transmission of radio signals between central offices and the cells. Millimeter wave (MMW) over fiber, on the other hand, offer high bandwidth for future high capacity mobile access. We propose and experimentally demonstrate a palm-shaped spectrum generation where the high-power central carrier can be used for upstream transmission while multiple MMW bands are capable of transmitting different downstream data simultaneously. Regarding optical datacenter networks, passive optical interconnects (POIs) have been proposed as an energy-efficient solution since only passive optical components are used for server interconnection. However, the high insertion loss may result in a scalability problem. We develop a methodology that considers various physical-layer aspects, e.g., receiver types, modulation formats, to quantify the scalability of POIs. Both theoretical analyses and experimental measurements have been performed to assess the scalability of various coupler-based POIs. / Den globala datatrafiken växer exponentiellt, både på grund av nya bandbreddskrävande applikationer och ökningen av antalet användare. Detta innebär en utmaning för kommunikationsnätens kapacitet. Fiberoptisk kommunikation är en framtidssäker teknik för att möta detta kapacitetsbehov och används redan i stor utsträckning i olika delar av näten. Beroende på överföringsavstånd, kan fibernät kategoriseras som långdistansnät eller nät med kort räckvidd. Denna avhandling behandlar nät med kort räckvidd, innefattande dels 1) accessnät som förbinder slutanvändarna till stadsnätet/ huvudnätet och typiskt omfattar tiotals kilometer, dels 2) optiska datanätverk som hanterar den interna trafiken inom datacenter med överföringsavstånd upp till ett par kilometer.För fiberaccessnät är en av de lovande teknikerna våglängdsmultiplexade passiva optiska nät (WDM-PON), där en dedicerad våglängdskanal tilldelas varje användare vilket garanterar hög datahastighet. Genom ett litet kanalavstånd så kan antalet användare i WDM-PON utökas men det gör samtidigt systemet känsligt för våglängdsdrift hos lasrarna. För att råda bot på detta, föreslår vi två system baserade på optisk frekvenskams-teknik. Vi validerar experimentellt att de kan generera stabila optiska bärvågor för WDM-PON. Radio-över –fiber-tekniken gör samtidigt det möjligt att sända radiosignaler över en lång sträcka och används därför i mobilsystem för överföring mellan centralstationen och radiocellerna. Millimetervågor (MMW) över fiber erbjuder ännu större modulationsbandbredd och är lovande för framtidens mobilradiosystem med hög kapacitet. I denna avhandling föreslår vi, och demonstrerar experimentellt, generation av ett frekvenskams-spektrum som är format som en handflata, där en central bärare med hög effekt (långfingret på handflatan) kan användas i radiocellerna för uppströms överföring, medan multipla MMW band (övriga fingrar) samtidigt kan överföra olika data nedströms. När det gäller nätverk för optiska datacenter, har passiva optiska interconnects (POI) föreslagits som en energieffektiv lösning, där endast passiva optiska komponenter används för ihopkoppling av servrarna. Höga inkopplingsförluster hos passiva optiska komponenter kan emellertid leda till allvarliga skalbarhetsproblem. I denna avhandling presenterar vi en nyutvecklad metod för att kvantifiera skalbarheten, vilken tar hänsyn till olika faktorer i det fysiska lagret som t.ex. mottagartyp och modulationsformat. Både teoretiska analyser och experimentella mätningar har utförts för att utvärdera skalbarheten hos olika kopplarbaserade POI. / <p>QC 20161117</p>

xiv, 138 p. : ill. (some col.) / In this dissertation, we demonstrate the generation of optical Raman frequency combs by a single laser pump pulse traveling in hydrogen-filled hollow-core optical fibers. This comb generation process is a cascaded stimulated Raman scattering effect, where higher-order sidebands are produced by lower orders scattered from hydrogen molecules. We observe more than 4 vibrational and 20 rotational Raman sidebands in the comb. They span more than three octaves in optical wavelength, largely thanks to the broadband transmission property of the fiber. We found that there are phase correlations between the generated Raman comb sidebands (spectral lines), although their phases are fluctuating from one pump pulse to another due to the inherit spontaneous initiation of Raman scattering. In the experiment, we generated two Raman combs independently from two fibers and simultaneously observed the single-shot interferences between Stokes and anti-Stokes components from the two fibers. The experimental results clearly showed the strong phase anti-correlation between first-order side bands. We also developed a quantum theory to describe this Raman comb generation process, and it predicts and explains the phase correlations we observe. The phase correlation that we found in optical Raman combs may allow us to synthesize single-cycle optical pulse trains, creating attosecond pulses. However, the vacuum fluctuation in stimulated Raman scattering will result in the fluctuation of carrier envelope phase of the pulse trains. We propose that we can stabilize the comb by simultaneously injecting an auxiliary optical beam, mutually coherent with the main Raman pump laser pulse, which is resonant with the third anti-Stokes field. / Committee in Charge: Dr. Steven van Enk, Chair; Dr. Michael G. Raymer; Dr. Daniel A. Steck; Dr. David M. Strom; Dr. Andrew H. Marcus

Optical frequency comb spectroscopy (OFCS) combines two previously exclusive features, i.e., wide optical bandwidth and high spectral resolution, enabling precise measurements of entire molecular bands and simultaneous monitoring of multiple gas species in a short measurement time. Moreover, the equidistant mode structure of frequency combs enables efficient coupling of the comb power to enhancement resonant cavities, yielding high detection sensitivities. Different broadband detection methods have been developed to exploit the full potential of frequency combs in spectroscopy, based either on Fourier transform spectroscopy or on dispersive elements.There have been two main aims of the research presented in this thesis. The first has been to improve the performance of mechanical Fourier transform spectrometers (FTS) based on frequency combs in terms of sensitivity, resolution and spectral coverage. In pursuit of this aim, we have developed a new spectroscopic technique, so-called noise-immune cavity-enhanced optical frequency comb spectroscopy (NICE-OFCS), and achieved a shot-noise-limited sensitivity and low ppb (parts-per-billion, 10−9) CO2 concentration detection limit in the near-infrared range using commercially available components. We have also realized a novel method for acquisition and analysis of comb-based FTS spectra, a so-called sub-nominal resolution method, which provides ultra-high spectral resolution and frequency accuracy (both in kHz range, limited only by the stability of the comb) over the broadband spectral range of the frequency comb. Finally, we have developed an optical parametric oscillator generating a frequency comb in the mid-infrared range, where the strongest ro-vibrational molecular absorption lines reside. Using this mid-infrared comb and an FTS, we have demonstrated, for the first time, comb spectroscopy above 5 μm, measured broadband spectra of several species and reached low ppb detection limits for CH4, NO and CO in 1 s.The second aim has been more application-oriented, focused on frequency comb spectroscopy in combustion environments and under atmospheric conditions for fast and sensitive multispecies detection. We have demonstrated, for the first time, cavity-enhanced optical frequency comb spectroscopy in a flame, detected broadband high temperature H2O and OH spectra using the FTS in the near-infrared range and showed the potential of the technique for flame thermometry. For applications demanding a short measurement time and high sensitivity under atmospheric pressure conditions, we have implemented continuous-filtering Vernier spectroscopy, a dispersion-based spectroscopic technique, for the first time in the mid-infrared range. The spectrometer was sensitive, fast, robust, and capable of multispecies detection with 2 ppb detection limit for CH4 in 25 ms. / Optisk frekvenskamspektroskopi (OFCS) kombinerar två tidigare icke förenliga egenskaper, dvs. ett brett optiskt frekvensområde med en hög spektral upplösning, vilket möjliggör noggranna mätningar av hela molekylära absorptionsband och detektion av flera gaser samtidigt med en kort mättid. Eftersom frekvenskammar har en regelbunden struktur med jämnt separerade laser moder kan man effektivt koppla kammen till en optisk kavitet och därmed möjliggöra frekvenskamsdetektion med hög känslighet. Olika metoder har utvecklats för att utnyttja frekvenskammarnas fulla potential för spektroskopi, baserad på antingen Fouriertransform-spektroskopi eller dispersiva element.Forskningen som presenteras i denna avhandling har haft två huvudmål. Det första har varit att förbättra prestandan hos mekaniska Fourier-transformspektrometrar (FTS) baserat på frekvenskammar med avseende på känslighet, upplösning och spektral täckning. I strävan efter detta har vi utvecklat en ny spektroskopisk teknik, benämnd brusimmun kavitetsförstärkt optisk frekvenskamspektroskopi (NICE-OFCS), och uppnått en hagelbrusbegränsad känslighet och detektionsgränser ner till låga ppb koncentrationer (miljarddelar, 10−9) för CO2 i det när-infraröda frekvensområdet enbart med användning av kommersiellt tillgängliga komponenter. Vi har också utvecklat en ny metod för insamling och analys av kambaserade FTS-spektra, som betecknas ha sub-nominell upplösning. Metoden gör det möjligt att uppnå ultrahög spektral upplösning och hög frekvensnoggrannhet (båda i kHz-området, endast begränsad av kammens stabilitet) över kammens hela frekvensområde. Slutligen har vi utvecklat en optisk parametrisk oscillator som genererar en frekvenskam i det mid-infraröda frekvensområdet, där de starkaste rotations-vibrationsmolekylära absorptionslinjerna finns. Med hjälp av denna kam och en FTS har vi för första gången demonstrerat frekvenskamspektroskopi över 5 μm. Vi har detekterat bredbandsspektra av flera molekylära gaser och har, för mättider på 1 s, uppnått detektionsgränser ner till låga ppb halter för CH4, NO och CO.Det andra syftet har varit mer applikationsorienterat: att använda frekvenskamspektroskopi i förbränningsmiljö och under atmosfäriska förhållanden för snabb och känslig multiämnesdetektion. Vi har för första gången demonstrerat kavitetsförstärkt optisk frekvenskamspektroskopi i en flamma, där vi har detekterat högtemperaturspektra av H2O och OH i det när-infraröda området med användning av FTS och visat teknikens potential för termometrisk karakterisering av flammor. För applikationer som kräver en kort mättid och hög känslighet under atmosfäriska förhållanden har vi utvecklat ett detektionssystem baserat på Vernier-spektroskopi med kontinuerlig filtrering, vilket är en dispersionsbaserad teknik, för första gången i det mid-infraröda frekvensområdet. Det befanns att spektrometern var känslig, snabb, robust och kapabel till multiämnesdetektion med en detektionsgräns på 2 ppb för CH4 för korta mättider (25 ms).

In this work, resonant laser spectroscopy has been utilized in two major projects --resonance fluorescence measurements in solid-state quantum-confined nanostructures and laser-induced fluorescence measurements in gases. The first project focuses on studying resonant light-matter interactions in semiconductor quantum dots "artificial atoms" with potential applications in quantum information science. Of primary interest is the understanding of fundamental processes and how they are affected by the solid-state matrix. Unlike atoms, quantum dots are susceptible to a variety of environmental influences such as phonon scattering and spectral diffusion. These interactions alter the desired properties of the scattered light and hinder uses in certain single photon source applications. One application of current interest is the use of quantum dots in “quantum repeaters” for which two-photon interference is key. Motivated by such an application we have explored the limits imposed by environmental effects on two quantum dots in the same sample, the scattered light from which is being interfered. We find that both one-photon and two-photon interference, although substantial, are affected in a variety of ways, in particular by spectral diffusion. These observations are discussed and compared with a theoretical model. We further investigated correlations in pulsed resonance fluorescence, and found significant unexpected spectral and temporal deviations from those studied under continuous wave excitation. Under these conditions, the scattered light exhibits Rabi oscillations and photon anti-bunching, while maintaining a rich spectrum containing many spectral features. These observations are discussed and compared with a theoretical model. In the second project, the focus is on the investigation of the possibility of detecting N2+ ions in air using laser induced fluorescence, with potential applications in detection of fissile materials at a distance. A photon-counting analysis reveals that the fluorescence decay rate rapidly increases with increasing N2 pressure and thus limits the detection at elevated pressures, in particular at atmospheric pressure. We show that time-gated detection can be used to isolate N2+ fluorescence from delayed N2 emission. Based on the spontaneous Raman signal from N2 simultaneously observed with N2+ fluorescence, we could estimate a limit of detection in air of order 108-1010 cm3.