<p>In this dissertation is exemplified how different laser based methods are applied in high-resolution spectroscopic studies of internal properties of diatomic molecules.</p><p>A molecular beam apparatus assembly is described, where a laser ablation source is combined with a time-of-flight mass spectrometer. Compounds investigated with this equipment are hafnium sulfide and hafnium oxide. The molecules are excited and ionized applying the resonant two-photon ionization (R2PI) scheme, which is a sensitive absorption and detection technique for probing the population of an excited state.</p><p>By means of the DC Stark effect, permanent electric dipole moments of HfS in the <i>D</i> ¹Π state and HfO in the <i>b</i> ³Π₁ state are determined while the molecules are exposed to a static electric field. Under field-free conditions low temperature rotationally resolved spectra are recorded, generating line positions from which molecular parameters are derived.</p><p>The R2PI method, modified with an adjustable delay time, is also used in lifetime measurements of individual rotational levels of the HfS <i>D</i>¹Π and HfO<i> b</i> ³Π₁ states. Oscillator strengths for transitions from the ground state are calculated, and in this connection basic concepts like Einstein coefficients, line strengths and Hönl-London factors, are surveyed. Theoretical calculation of lifetimes is discussed in view of the fact that a commonly available computer program (LEVEL 7.5 by Le Roy) gives erroneous output.</p><p>Some coherence and quantum interference related phenomena, such as electromagnetically induced transparency (EIT) and Autler-Townes (AT) splitting, are presented in the latter part of this thesis. Fundamental concepts and relations are introduced and explained. The driven three-level cascade system is elucidated, including some of its experimental applications to alkali metal dimers, Na₂ and Li₂.</p><p>A triple resonance spectroscopy experiment is described in terms of a three-laser, four-level inverted-Y excitation scheme, implemented in Na₂. The accompanying density matrix formalism, providing the basis for theoretical simulations, is accounted for. From analysis of the results an absolute value of the electric dipole moment matrix element (transition moment) is extracted, using the AC Stark effect.</p><p>Some recently reported unexpected experimental results and unforeseen features, occurring in Doppler broadened samples and related to the open character of molecular systems, are briefly commented.</p>

In this dissertation is exemplified how different laser based methods are applied in high-resolution spectroscopic studies of internal properties of diatomic molecules. A molecular beam apparatus assembly is described, where a laser ablation source is combined with a time-of-flight mass spectrometer. Compounds investigated with this equipment are hafnium sulfide and hafnium oxide. The molecules are excited and ionized applying the resonant two-photon ionization (R2PI) scheme, which is a sensitive absorption and detection technique for probing the population of an excited state. By means of the DC Stark effect, permanent electric dipole moments of HfS in the D 1Π state and HfO in the b 3Π1 state are determined while the molecules are exposed to a static electric field. Under field-free conditions low temperature rotationally resolved spectra are recorded, generating line positions from which molecular parameters are derived. The R2PI method, modified with an adjustable delay time, is also used in lifetime measurements of individual rotational levels of the HfS D 1Π and HfO b 3Π1 states. Oscillator strengths for transitions from the ground state are calculated, and in this connection basic concepts like Einstein coefficients, line strengths and Hönl-London factors, are surveyed. Theoretical calculation of lifetimes is discussed in view of the fact that a commonly available computer program (LEVEL 7.5 by Le Roy) gives erroneous output. Some coherence and quantum interference related phenomena, such as electromagnetically induced transparency (EIT) and Autler-Townes (AT) splitting, are presented in the latter part of this thesis. Fundamental concepts and relations are introduced and explained. The driven three-level cascade system is elucidated, including some of its experimental applications to alkali metal dimers, Na2 and Li2. A triple resonance spectroscopy experiment is described in terms of a three-laser, four-level inverted-Y excitation scheme, implemented in Na2. The accompanying density matrix formalism, providing the basis for theoretical simulations, is accounted for. From analysis of the results an absolute value of the electric dipole moment matrix element (transition moment) is extracted, using the AC Stark effect. Some recently reported unexpected experimental results and unforeseen features, occurring in Doppler broadened samples and related to the open character of molecular systems, are briefly commented.

Strong coherence in quasi-resonant laser driven system interferes with effective relaxations, resulting in behaviors like, coherent population trapping and Electromagnetically induced transparency. The Raman system can optimize this utilizing excited coherence in the lambda system when exposed to counter- intuitive pump-stokes pulses. The phenomenon can result in complete population transfer between vibrational levels called Stimulated Raman adiabatic passage(STIRAP). STIRAP and CHIRAP have been studied with Gaussian and chirped pulses. The optical propagation effects in dense medium for these phenomenon is studied to calculate the limitations and induced coherences. Further, the effect of rotational levels has been investigated. The molecular vibrational coherence strongly depends on the effect of rotational levels. The change in coherence interaction for ro-vibrational levels are reported and explained. We have considered the effects on the phase of radiation related to rotational mechanical motion of quantum system by taking advantages in ultra strong dispersion medium provided by quantum coherence in lambda system. The enhanced Fizeau effect on a single atom is observed.

Optical response of an active medium can substantially be modified when coherent superpositions of states are excited, that is, when systems display quantum coherence and interference. This has led to fascinating applications in atomic and molecular systems. Examples include coherent population trapping, lasing without inversion, electromagnetically induced transparency, cooperative spontaneous emission, and quantum entanglement. We study quantum coherence effects in several quantum optical systems and find interesting applications. We show that quantum coherence can lead to transient Raman lasing and lasing without inversion in short wavelength spectral regions--extreme ultraviolet and x-ray--without the requirement of incoherent pumping. For example, we demonstrate transient Raman lasing at 58.4 nm in Helium atom and transient lasing without inversion at 6.1 nm in Helium-like Boron (triply-ionized Boron). We also investigate dynamical properties of a collective superradiant state prepared by absorption of a single photon when the size of the sample is larger than the radiation wavelength. We show that for large number of atoms such a state, to a good approximation, decays exponentially with a rate proportional to the number of atoms. We also find that the collective frequency shift resulting from repeated emission and reabsorption of short-lived virtual photons is proportional to the number of species in the sample. Furthermore, we examine how a position-dependent excitation phase affects the evolution of entanglement between two dipole-coupled qubits. It turns out that the coherence induced by position-dependent excitation phase slows down the otherwise fast decay of the two-qubit entanglement. We also show that it is possible to entangle two spatially separated and uncoupled qubits via interaction with correlated photons in a cavity quantum electrodynamics setup. Finally, we analyze how quantum coherence can be used to generate continuous-variable entanglement in quantum-beat lasers in steady state and propose possible implementation in quantum lithography.

[pt] O bunching de fótons é um dos mais celebrados efeitos de interferência de dois fóotons, associado à tendéncia de fótons indistinguíveis de tomarem o mesmo caminho quando há uma superposição dos pacotes de onda em um combinador de feixes óptico simétrico. Nós exploramos o fenômeno de interferência de dois fótons e mostramos que: a característica espectral de uma fonte de luz pode ser determinar através da técnica de Espectroscopia de Transformada de Fourier de Poucos Fótons de alta resolução que se mostra como uma técnica útil para a caracterização espectral de fontes ópticas débeis abaixo do limite coberto por técnicas clássicas de batimento heteródino; uma fonte de fótons com estatística sub-Poisson, a Fonte de Fótons Anunciadas com Óptica Linear, pode ser construída baseada apenas em óptica linear e estados coerentes atenuados uma vez que os anúncios sejam sintonizados nos picos de coincidência de um interferograma de Hong-Ou-Mandei quando o interferômetro é alimentado com estados em frequências diferentes; uma modificação do interferômetro de Hong-Ou-Mandel produz um aumento no número de coincidências, ao invés de sua diminuição, quando os pacotes de onda estão perfeitamente superpostos no interferômetro e o anúncio de fótons sintonizados nesse pico gera um feixe com distribuição sub-Poisson. A descrição matemática de cada experimento é detalhada e uma revisão extensa das ferramentas teóricas e práticas necessárias para o entendimento dos resultados é apresentada. / [en] Photon bunching is one of the most celebrated effects of two-photon interference, related to the tendency of indistinguishable photons to take the same path when there is a wave-packet overlapping in a symmetric beam splitter. Photon antibunching, the counterpart of photon bunching is, on turn, a desired effect in many applications such as single-photon generation. We explore the two-photon interference phenomena and show that: the spectral characteristics of a light source can be determined with a high resolution Few-Photon Fourier Transform Spectroscopy which proves to be a useful asset for spectral characterization of faint optical sources below the range covered by classical heterodyne beating techniques; a sub-Poisson photon source, the Linear-Optic Heralded Photon Source, can be constructed based only on linear optics and weak coherent states by time-tuning a Hong-Ou-Mandel interferometer fed with frequency-displaced coherent states and yields a second-order correlation function at zero time below one; a modified version a the Hong-Ou-Mandel interferometer produces a peak of coincidences instead of dip when the wave-packets are perfectly overlapped and the announcement of photons time-tuned to this coincidence peak yield an antibunched photon stream. The mathematical description of each experiment is detailed and an extensive review of the most important theoretical and practical tools for understanding of the results is presented.

The present series of studies examine how jurors and public defenders evaluate different pieces of evidence and integrate them into a coherent conclusion within the context of a criminal case. Previous research has shown that in situations where both sides of the case are compelling, decision-makers nevertheless come to highly confident and polarized decisions, called coherence shifts (Simon, 2004). The present research sought to expand on coherence effects, improve upon the methodology of previous studies, and explore potential moderators of coherence. In Study 1, mock jurors (n = 306) read about a criminal case and evaluated multiple pieces of evidence at various points throughout the case. Results indicated that participants exhibited pronounced coherence shifts (i.e., their evaluations of the various pieces of evidence (a) became more consistent as the case progressed, and (b) were evaluated in line with their initial leanings) using an improved methodology that randomized evidence order and evidence valence. Furthermore, participants’ interim leanings of guilt or innocence biased their subsequent evaluations of ambiguous evidence. The direction and magnitude of participants’ coherence shifts were predicted by their pretrial dispositions towards prosecution and defense. Participants lacked awareness of how their perceptions of the evidence have shifted. Coherence shifts were not, however, moderated by asking mock jurors to justify their decisions, or by asking mock jurors to play devil’s advocate while considering each piece of evidence, underscoring the pervasiveness of this cognitive bias. Study 2 examined whether actual public defenders experience coherence shifts and how those shifts relate to the plea bargaining process; however, no coherence shifts were observed. Study 3 examined whether the timing of the defense’s presentation of their case could reduce coherence effects; results indicated that reading about the defense’s case immediately after the prosecution’s case (c.f. following a delay) marginally (p = .09) reduced coherence effects among jurors who acquitted the defendant, suggesting one potential strategy to mitigate this bias.