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We report on the generation of twin beams through a cascaded process of optical parametric oscillation in a doubly resonant second-harmonic generation system. These bright beams exhibit strong quantum correlations, enabling the observation of up to 5 dB of noise reduction in their intensity difference below the standard quantum limit.
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We report on the experimental realization and a systematic study of optical frequency comb generation in doubly resonant intracavity second harmonic generation (SHG). The efficiency of intracavity nonlinear processes usually benefits from the increasing number of resonating fields. Yet, achieving the simultaneous resonance of different fields may be technically complicated, all the more when a phase matching condition must be fulfilled as well. In our cavity we can separately control the resonance condition for the fundamental and its second harmonic, by simultaneously acting on an intracavity dispersive element and on a piezo-mounted cavity mirror, without affecting the quasi-phase matching condition. In addition, by finely adjusting the laser-to-cavity detuning, we are able to observe steady comb emission across the whole resonance profile, revealing the multiplicity of comb structures, and the substantial role of thermal effects on their dynamics. Lastly, we report the results of numerical simulations of comb dynamics, which include photothermal effects, finding a good agreement with the experimental observations. Our system provides a framework for exploring the richness of comb dynamics in doubly resonant SHG systems, assisting the design of chip-scale quadratic comb generators.
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By reducing both the internal and translational temperature of any species down to a few kelvins, the buffer-gas-cooling (BGC) technique has the potential to dramatically improve the quality of ro-vibrational molecular spectra, thus offering unique opportunities for transition frequency measurements with unprecedented accuracy. However, the difficulty in integrating metrological-grade spectroscopic tools into bulky cryogenic equipment has hitherto prevented from approaching the kHz level even in the best cases. Here, we overcome this drawback by an original opto-mechanical scheme which, effectively coupling a Lamb-dip saturated-absorption cavity ring-down spectrometer to a BGC source, allows us to determine the absolute frequency of the acetylene (ν1 + ν3) R(1)e transition at 6561.0941 cm-1 with a fractional uncertainty as low as 6 × 10-12. By improving the previous record with buffer-gas-cooled molecules by one order of magnitude, our approach paves the way for a number of ultra-precise low-temperature spectroscopic studies, aimed at both fundamental Physics tests and optimized laser cooling strategies.
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Optical frequency combs are one of the most remarkable inventions in recent decades. Originally conceived as the spectral counterpart of the train of short pulses emitted by mode-locked lasers, frequency combs have also been subsequently generated in continuously pumped microresonators, through third-order parametric processes. Quite recently, direct generation of optical frequency combs has been demonstrated in continuous-wave laser-pumped optical resonators with a second-order nonlinear medium inside. Here, we present a concise introduction to such quadratic combs and the physical mechanism that underlies their formation. We mainly review our recent experimental and theoretical work on formation and dynamics of quadratic frequency combs. We experimentally demonstrated comb generation in two configurations: a cavity for second harmonic generation, where combs are generated both around the pump frequency and its second harmonic and a degenerate optical parametric oscillator, where combs are generated around the pump frequency and its subharmonic. The experiments have been supported by a thorough theoretical analysis, aimed at modelling the dynamics of quadratic combs, both in frequency and time domains, providing useful insights into the physics of this new class of optical frequency comb synthesizers. Quadratic combs establish a new class of efficient frequency comb synthesizers, with unique features, which could enable straightforward access to new spectral regions and stimulate novel applications.
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We review the recent developments in precision ro-vibrational spectroscopy of buffer-gas-cooled neutral molecules, obtained using infrared frequency combs either as direct probe sources or as ultra-accurate optical rulers. In particular, we show how coherent broadband spectroscopy of complex molecules especially benefits from drastic simplification of the spectra brought about by cooling of internal temperatures. Moreover, cooling the translational motion allows longer light-molecule interaction times and hence reduced transit-time broadening effects, crucial for high-precision spectroscopy on simple molecules. In this respect, we report on the progress of absolute frequency metrology experiments with buffer-gas-cooled molecules, focusing on the advanced technologies that led to record measurements with acetylene. Finally, we briefly discuss the prospects for further improving the ultimate accuracy of the spectroscopic frequency measurement.
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Acetileno/química , Modelos Teóricos , Espectrofotometria Infravermelho , AlgoritmosRESUMO
We report on a widely (2.25 THz or 75 cm(-1)) and rapidly (4.5 THz/s) mode-hop-free (MHF) tunable mid-IR laser source at ~3.3 µm, consisting of a 5%-MgO:LiNbO(3) singly resonant optical parametric oscillator (SRO) pumped by an automated broadly MHF tunable extended-cavity diode laser (ECDL). The broad and rapid MHF tuning capability of the ECDL is readily transferred to the SRO idler wave owing to the quasi-noncritical pump spectral acceptance bandwidth of the quasi-phase-matching. Fast and broadband high-resolution Doppler spectroscopy measurements of the ν(3) band of CH(4) are presented to illustrate the performance of the mid-IR optical parametric oscillator spectrometer.
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We report a thorough analysis of the spectral properties of an ytterbium-doped fibre amplifier, seeded by a Nd:YAG laser, whose linewidth has been narrowed down to 1 Hz by locking the laser to an ultrastable reference cavity. We measured the phase noise contribution from the amplifier, showing that it does not depend on the amplification gain, nor on the seed laser linewidth. Moreover, the amplifier-induced phase noise does not affect the final linewidth, as verified by heterodyne linewidth measurement within the 0.2 Hz resolution bandwidth of our acquisition set-up. Preservation of spectral purity below Hz-level is promising for more demanding applications, from nonlinear optics to frequency/time-standard transfer over fibre links.
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Amplificadores Eletrônicos , Artefatos , Tecnologia de Fibra Óptica/instrumentação , Lasers de Estado Sólido , Desenho de Equipamento , Análise de Falha de Equipamento , Razão Sinal-RuídoRESUMO
A 16-year-old young man presented with an atypical Spitz tumour of the left buttock with involvement of the left inguinal sentinel node. After inguinal lymphadenectomy, none among the further 21 left inguinal lymph nodes excised was positive. The patient has been free of disease for 39 months. Reviewing published reports, 68 of 147 patients with atypical Spitz tumours having sentinel node mapping had positive nodes. Complete nodal dissection was performed in 66 of these 68 patients. All these patients with a positive sentinel node including this patient were alive and disease-free, with a mean follow-up of 35.8 months. Doubts about the exact nature of atypical Spitz tumours still persist. Although it does not seem to behave like conventional melanomas since prognosis is highly favourable despite a high incidence of sentinel node deposits, interpretations of these nodal involvements are still debated. A longer follow-up period of surveillance should be useful to definitively disclose this question. A literature review to provide an analysis of current knowledge regarding diagnosis, management, and treatment options was undertaken. Furthermore, current misconcepts leading to under-treatment as well as over-treatment, new trends in diagnosis, and surgical approach are discussed. The real biologic potential of the disease could not often be evaluated by sentinel lymph node status. Although this procedure may have a role, possibly being therapeutic for those patients who have malignant lesions, it produces morbidity and outcomes that are sometimes difficult to interpret in this type of pigmented lesions. Thus, it should be reserved to selected patients.
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Nevo de Células Epitelioides e Fusiformes/patologia , Neoplasias Cutâneas/patologia , Adolescente , Nádegas , Humanos , Imuno-Histoquímica , Excisão de Linfonodo , Masculino , Nevo de Células Epitelioides e Fusiformes/metabolismo , Biópsia de Linfonodo Sentinela , Neoplasias Cutâneas/metabolismoRESUMO
Primary malignant melanoma involving the nasal and paranasal sinus mucosa is a rare neoplasm, accounting for less than 1% of all melanomas. Being more aggressive than its cutaneous counterpart, it carries a poor prognosis. We report a case arising from the nasal septum mucosae in a 78-year-old man. We describe clinical features, diagnosis, and treatment of this rare disease along with a review of the pertinent literature. Endoscopic resection of the neoplasm was performed, enabling diagnosis of sinonasal mucosal melanoma involving the frontal sinus floor. Because the patient was too compromised to achieve radical surgical approach (craniofacial resection), he underwent radiation therapy. Through this article, we wish to emphasize that early diagnosis with a high index of suspicion is critical because this type of tumor is extremely aggressive. Its location and relatively nonspecific features frequently delay diagnosis, and its rarity avoids an optimal treatment guideline setting.
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Melanoma/diagnóstico , Septo Nasal/patologia , Neoplasias Nasais/diagnóstico , Idoso , Endoscopia , Evolução Fatal , Seio Frontal/patologia , Humanos , Masculino , Mucosa Nasal/patologia , Terapia Neoadjuvante , Invasividade Neoplásica , Neoplasias dos Seios Paranasais/diagnóstico , Radioterapia AdjuvanteRESUMO
We report on efficient cw high-power second harmonic generation in a periodically poled LiTaO3 crystal placed in a resonant enhancement cavity. We tested three configurations, differing in the coupling mirror reflectivity, and a maximum conversion efficiency of about 76%, corresponding to 6.1 W of green light with 8.0 W of fundamental power, was achieved. This is, to the best of our knowledge, the highest cw power ever reported using a periodically-poled crystal in an external cavity. We observed photo-thermal effect induced by photon absorption at the mirrors and in the crystal, which however does not affect stable operation of the cavity. A further effect arises for two out of the three configurations, at higher values of the input power, which degrades the performance of the locked cavity. We suggest this effect is due to the onset of competing nonlinearities in the same crystal.
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Iluminação/instrumentação , Lítio/química , Dispositivos Ópticos , Óxidos/química , Tantálio/química , Transferência de Energia , Desenho de Equipamento , Análise de Falha de Equipamento , Luz , Lítio/efeitos da radiação , Óxido de Magnésio/química , Óxido de Magnésio/efeitos da radiação , Óxidos/efeitos da radiação , Tantálio/efeitos da radiaçãoRESUMO
We report on a continuous-measurement campaign carried out in Vulcano (Aeolian islands, Sicily), devoted to the simultaneous monitoring of CO2 and H2O concentrations. The measurements were performed with an absorption spectrometer based on a semiconductor laser source emitting around a 2-microm wavelength. The emitted radiation was selectively absorbed by two molecular ro-vibrational transitions specific of the investigated species. Data for CO2 and H2O concentrations, and CO2 soil diffusive flux using an accumulation chamber configuration, were collected at several interesting sampling points on the island (Porto Levante beach- PLB, Fossa Grande Crater - FOG- and Valley of Palizzi, PAL). CO2/H2O values, measured on the ground, are very similar (around 0.019 (+/- 0.006)) and comparable to the previous discrete detected values of 0.213 (Fumarole F5-La Fossa crater rim) and 0.012 (Fumarole VFS - Baia Levante beach) obtaid during the 1977-1993 heating phase of the crater fumaroles. In this work much more homogeneous values are found in different points of the three sites investigated. The field work, although carried out in a limited time window (25th-28th August 2004), pointed out the new apparatus is suitable for continuous gas monitoring of the two species and their ratios, which are important geochemical indicators of volcanic activity, for which other reliable continuous monitoring systems are not yet available.