Real-Time Optical Time Interpolation Using Spectral Interferometry

A simple scheme for all-optical time interpolation using spectral interferometry is put forward that is in principle capable of single-shot measurements. In this method, the arrival time of optical timing pulses is encoded into the spectrum of a time-stretched supercontinuum via cross-phase modulation. The proof-of-concept test setup points toward femtosecond-level absolute timing capabilities with only minor additions to modern optical clockwork

Open-loop polarization mode dispersion mitigation for fibre-optic time and frequency transfer

The non-reciprocal and dynamic nature of polarization mode dispersion (PMD) in optical fibers can be a problem for accurate time and frequency transfer. Here a simple, passive solution is put forward that is based on transmitting optical pulses with alternating orthogonal polarization. The fast and deterministic polarization modulation means that the PMD noise is pushed far away from the frequencies of interest and upon reflection from a Faraday mirror at the receiver, the pulses have a well defined polarization when they return to the transmitter, which facilitates stable optical phase detection and fibre phase compensation. In an open-loop test setup that uses a mode-locked laser and a simple pulse interleaver, the polarization mode dispersion is shown to be reduced by more than two orders of magnitud

Dynamics of free-running, pump-modulated and coupled semiconductor and solid-state lasers

The output of a laser is a high frequency propagating electromagnetic field with superior coherence and brightness compared to that emitted by thermal sources. A multitude of different types of lasers exist, which also translates into large differences in the properties of their output. Moreover, the characteristics of the electromagnetic field emitted by a laser can be influenced from the outside, e.g., by injecting an external optical field or by optical feedback. In the case of free-running solitary class-B lasers, such as semiconductor and Nd:YVO4 solid-state lasers, the phase space is two-dimensional, the dynamical variables being the population inversion and the amplitude of the electromagnetic field. The two-dimensional structure of the phase space means that no complex dynamics can be found. If a class-B laser is perturbed from its steady state, then the steady state is restored after a short transient. However, as discussed in part (i) of this Thesis, the static properties of class-B lasers, as well as their artificially or noise induced dynamics around the steady state, can be experimentally studied in order to gain insight on laser behaviour, and to determine model parameters that are not known ab initio. In this Thesis particular attention is given to the linewidth enhancement factor, which describes the coupling between the gain and the refractive index in the active material. A highly desirable attribute of an oscillator is stability, both in frequency and amplitude. Nowadays, however, instabilities in coupled lasers have become an active area of research motivated not only by the interesting complex nonlinear dynamics but also by potential applications. In part (ii) of this Thesis the complex dynamics of unidirectionally coupled, i.e., optically injected, class-B lasers is investigated. An injected optical field increases the dimensionality of the phase space to three by turning the phase of the electromagnetic field into an important variable. This has a radical effect on laser behaviour, since very complex dynamics, including chaos, can be found in a nonlinear system with three degrees of freedom. The output of the injected laser can be controlled in experiments by varying the injection rate and the frequency of the injected light. In this Thesis the dynamics of unidirectionally coupled semiconductor and Nd:YVO4 solid-state lasers is studied numerically and experimentally.Det finns många olika typer av lasrar, vilket också betyder att egenskaperna hos det ljus som lasrar emitterar varierar mycket. Därtill kan egenskaperna hos laserljus ändras genom till exempel optisk injektion. Vid optisk injektion injiceras ljus in i en laser från en extern ljuskälla, som oftast är en annan liknande laser. I den här avhandlingen har dynamiken hos frigående, modulerade och optiskt injicerade halvledar- och fasta tillståndets lasrar undersökts experimentellt och numeriskt. Frigående halvledar- och fasta tillståndets lasrar har två frihetsgrader: amplituden på det elektromagnetiska fältet (uteffekt) och populationsinversionen i det aktiva området (mängden exciterade atomer). Om en sådan laser störs från sitt jämviktsläge återgår den snabbt tillbaka till jämviktsläget via ett fåtal oscillationer. Frigående lasrar av ovannämnda typer uppvisar med andra ord inte komplicerad (och intressant) dynamik. Däremot kan man undersöka artificiellt eller brus inducerad dynamik runt jämviktsläget i syfte att mäta olika parametrar som beskriver egenskaper hos dessa lasrar. I avhandlingens första del har stor vikt satts på att experimentellt mäta den så kallade alfa-faktorn, som beskriver kopplingen mellan förstärkningen och brytningsindexet i laserns aktiva del. Med andra ord kvantifierar alfa-faktorn kopplingen mellan det emitterade ljusets amplitud och fas. I avhandlingens andra del har dynamiken under optisk injektion undersökts. Injektion av ljus från en annan laser ändrar radikalt på lasrarnas beteende. Det beror på att det injicerade ljuset omvandlar fasen på det elektromagnetiska fältet till en viktig variabel och ökar således antalet frihetsgrader från två till tre. Beroende på det injicerade ljusets effekt och frekvens, kan den icke-linjära växelverkan ge upphov till bland annat stabila, periodiska och kaotiska tillstånd i lasern. Optiskt injicerade halvledarlasrar har en del nutida tillämpningar och även några potentiella framtida tillämpningar. I dagsläget används optisk injektion till att förstärka svagt ljus av god kvalitet och till karakterisering av lasrar. I framtiden kan optisk injektion även finna tillämpningar inom telekommunikationsindustrin och radarteknologin. Optiskt injicerade lasrar och andra typer av kopplade lasersystem är dock inte endast intressanta tack vare tillämpningarna. Dessa lättkontrollerade system ger också goda möjligheter att experimentellt studera egenskaper hos icke-linjära dynamiska system

Reason-Resilience and security of geospatial data for critical infrastructures

Peer reviewe

Characterization of broadband few-cycle laser pulses with the d-scan technique

We present an analysis and demonstration of few-cycle ultrashort laser pulse characterization using second-harmonic dispersion scans and numerical phase retrieval algorithms. The sensitivity and robustness of this technique with respect to noise, measurement bandwidth and complexity of the measured pulses is discussed through numerical examples and experimental results. Using this technique, we successfully demonstrate the characterization of few-cycle pulses with complex and structured spectra generated from a broadband ultrafast laser oscillator and a high-energy hollow fiber compressor. (C)2012 Optical Society of Americ

FIN-EPOS – Finnish national node of the European Plate Observing System

Non peer reviewe

Frequency-comb-referenced mid-infrared source for high-precision spectroscopy

We report on a tunable continuous-wave mid-infrared optical parametric oscillator (OPO), which is locked to a fully stabilized near-infrared optical frequency comb using a frequency doubling scheme. The OPO is used for 40 GHz mode-hop-free, frequency-comb-locked scans in the wavelength region between 2.7 and 3.4 x03BC;m. We demonstrate the applicability of the method to high-precision cavity-ring-down spectroscopy of nitrous oxide (N2O) and water (H2O) at 2.85 x00B5;m and of methane (CH4) at 3.2 x03BC;m.Peer reviewe

Simultaneous compression and characterization of ultrashort laser pulses using chirped mirrors and glass wedges

We present a simple and robust technique to retrieve the phase of ultrashort laser pulses, based on a chirped mirror and glass wedges compressor. It uses the compression system itself as a diagnostic tool, thereby making unnecessary the use of complementary diagnostic tools. We used this technique to compress and characterize 7.1 fs laser pulses from an ultrafast laser oscillator.Comment: 10 pages, 5 figure

Driving a low critical current Josephson junction array with a mode-locked laser

Data for article "Driving a low critical current Josephson junction array with a mode-locked laser"

Photoemission-time-delay measurements and calculations close to the 3s-ionization-cross-section minimum in Ar

We present experimental measurements and theoretical calculations of photoionization time delays from the 3s and 3p shells in Ar in the photon energy range of 32-42 eV. The experimental measurements are performed by interferometry using attosecond pulse trains and the infrared laser used for their generation. The theoretical approach includes intershell correlation effects between the 3s and 3p shells within the framework of the random-phase approximation with exchange. The connection between single-photon ionization and the two-color two-photon ionization process used in the measurement is established using the recently developed asymptotic approximation for the complex transition amplitudes of laser-assisted photoionization. We compare and discuss the theoretical and experimental results, especially in the region where strong intershell correlations in the 3s -> kp channel lead to an induced "Cooper" minimum in the 3s ionization cross section