Abstract In this work, we describe an interferometric method to generate ultra-short pulses below the Fourier limit. It is done by extending concepts first developed in the spatial domain to achieve sub-diffractive beams through the addition of a spatial chirp in one of the arms of a Michelson interferometer using a spherical mirror. To experimentally synthesize sub-Fourier pulses, we replace the spherical mirror with a water cell, since it produces chirp in the temporal domain. We also present an alternative procedure, based on asymmetrical interference between the widened pulse and the original pulse where the peaks of both pulses exhibit a temporal delay achieving the narrowing of ultra-short pulses with sub-Fourier scales. To characterize the performance of the system, we performed a preliminary assessment considering the percentage of full width at half-maximum shrinking obtained for each scheme. By means of a symmetrical configuration, 7% and 12% pulse reductions were verified, both experimentally and analytically, while for the non-symmetrical configuration, 10% and 24% reductions were achieved corresponding to main lobe to side-lobe ratios of 10% and 30%. The experimental setup scheme is simple, versatile and able to work with high-power laser sources and ultra-short pulses with a broad bandwidth at any central wavelength. The results presented in this work are promising and help to enlighten new routes and strategies in the design of coherent control systems. We envision that they will become broadly useful in different areas from strong field domain to quantum information.
Abstract In this work, we describe an interferometric method to generate ultra-short pulses below the Fourier limit. It is done by extending concepts first developed in the spatial domain to achieve sub-diffractive beams through the addition of a spatial chirp in one of the arms of a Michelson interferometer using a spherical mirror. To experimentally synthesize sub-Fourier pulses, we replace the spherical mirror with a water cell, since it produces chirp in the temporal domain. We also present an alternative procedure, based on asymmetrical interference between the widened pulse and the original pulse where the peaks of both pulses exhibit a temporal delay achieving the narrowing of ultra-short pulses with sub-Fourier scales. To characterize the performance of the system, we performed a preliminary assessment considering the percentage of full width at half-maximum shrinking obtained for each scheme. By means of a symmetrical configuration, 7% and 12% pulse reductions were verified, both experimentally and analytically, while for the non-symmetrical configuration, 10% and 24% reductions were achieved corresponding to main lobe to side-lobe ratios of 10% and 30%. The experimental setup scheme is simple, versatile and able to work with high-power laser sources and ultra-short pulses with a broad bandwidth at any central wavelength. The results presented in this work are promising and help to enlighten new routes and strategies in the design of coherent control systems. We envision that they will become broadly useful in different areas from strong field domain to quantum information.
Interference has long been used for precision measurement of path-length changes. Since the advent of the laser, interference has become one of the most versatile tools in metrology. Specifically, ultra-short laser pulses allow unprecedented resolution in absolute length measurements. While ultra-short laser pulses lead to high resolution, for example in white-light interferometry, they are very susceptible to dispersion. \n \nQuantum resources have been proposed to overcome some of the problems related to distortions in the interferometric signal. For example, the Hong-Ou-Mandel (HOM) interferometer relies on frequency-entangled photon pairs and features automatic even-order dispersion cancellation and high interference visibility resilient to unbalanced loss. Quantum-OCT is a technique based on HOM interferometry, that promises to overcome Optical Coherence Tomography (OCT) a classical imaging technique based on low coherence light. Furthermore, straightforward modifications of the HOM interferometer can display several different interferometric signals, including the HOM peak, quantum beating, and phase super-resolution. However, the quantum resources required are hard to produce and dim, leading to long integration times and single-photon counting. \n \nIn this thesis, we introduce the theory behind Chirped-Pulse Interferometry (CPI), a new technique that combines all the advantages of Q-OCT, including even-order dispersion cancellation, but without the need for any quantum resources. We then experimentally implement CPI and demonstrate all the important characteristics shared by the HOM interferometer, but at dramatically larger signal levels. We show how CPI can be used to measure dispersion cancelled axial profiles of an optical sample and show the improvement in resolution over white-light interferometry. Finally, we show that by modifying CPI in analogous ways to HOM, CPI can also be made to produce interferometric signal identical to the HOM peak, quantum beating, and phase super-resolution.
Ultra-broadband frequency entangled biphotons have exceptionally short temporal duration and can achieve narrow Hong–Ou–Mandel (HOM) interference patterns, making them vital for quantum metrology applications. However, the bandwidth of previously demonstrated biphotons used for HOM interference has been limited to less than 400 nm, which is not wide enough to achieve ultra-high precision in quantum metrology. In order to push the precision to its limit, we have theoretically designed a 20-mm-long chirped periodically poled lithium niobate (CPPLN) crystal with type-II phase matching. Pumped by a 405 nm laser, the down-converted signal and idler photons can cover the wavelength range from 420 to 5200 nm, approaching the transparent upper bound of the LN crystal. In the simulated Hong–Ou–Mandel (HOM) interference, the full-width at half-maximum of the interference pattern is 965 attoseconds, with a visibility of 99.44%. Following a similar approach, we also designed a type-0 CPPLN crystal to achieve higher brightness. These ultra-broadband biphoton sources can generate ultra-narrow quantum interference patterns, which have the potential for attosecond-level high-precision quantum metrology.
We present here a theoretical analysis of the interaction between an ideal two-level quantum system and a super-oscillatory pulse, like the one proposed and successfully synthesized in Ref. this http URL. As a prominent feature, these pulses present a high efficiency of the central super-oscillatory region in relation to the unavoidable side-lobes. Besides, our study shows an increase of the global bandwidth of the pulse, in the super-oscillatory region, and not only the appearance of a frequency higher than its highest Fourier-frequency component, as in the usual description of the phenomenon of super-oscillations. Beyond introducing the concept of super-bandwidth, the presented results could be relevant for experimental applications and opening new perspectives for laser-matter interaction.
Throughout the past few decades, science has progressed towards the ability to probe many extremely fast processes and a large amount of research has been aimed at the area of few-femtosecond pulse generation. This thesis describes the generation of coherent broadband radiation through two-colour pumping of molecular hydrogen confined to a unidirectional ring cavity, and the subsequent synthesis of high peak power and few-femtosecond pulses. A set of normalised semi-classical field equations are derived in Bloch form describing the process of ultra-broadband multi-frequency Raman generation or UMRG, and a 3-wave gain suppression analysis is derived from a subset of the plane wave UMRG field equations which describes gain suppression within the ring cavity in terms of both medium and cavity parameters. The gain suppression analysis is further generalised to include finite levels of linear two-photon frequency detuning of the pump beams. Simulations of the plane wave ultra-broadband multi-frequency Raman (UMRG) equations show that a broad frequency spectrum of mutually coherent sideband can be generated. The inverse Fourier transform of spectra generated in this way yields a train of high power near Fourier limited pulses in the time domain which can range from a few-femtoseconds in duration to tens of attoseconds with repetition rates equal to the Raman transition frequency. Pulses synthesised in this way are limited only by the level of medium dispersion, the reflection bandwidth of the chosen coupling mirror and the chosen Raman medium. Simulations of the transverse UMRG equations within the ring cavity geometry have shown ring cavity enhanced UMRG to be resilient to transverse effects such as finite beam width, beam diffraction and the transverse beam separation of the applied pump beams.
We have studied sub-optical wavelength atomic gratings generated by the interference of atomic de Broglie waves in a time-domain interferometer. Three short optical standing- wave pulses, detuned from resonance with a cloud of approximately 100 (mu) K 85Rb atoms, act as phase gratings for atomic matter waves. Shortly after the first pulse, a modulation in the atomic density containing spatial harmonics of period (lambda) /2N appears ((lambda) is the optical wavelength, and N is any integer) and then rapidly vanishes due to the atomic thermal motion. The cloud maintains phase memory of this modulation, however, and the second pulse (applied at time T after the first one) results in a temporal sequence of atomic density gratings of periods (lambda) /2N. The appearance of a grating is referred to as an echo. The third pulse (and a subsequent traveling wave pulse) is used to detect these gratings. By this technique, we have created and detected in real time a grating with period (lambda) /4 at time 1.5T after the first pulse and observed new types of `echoes' caused by interaction of the de Broglie waves with all three phase gratings. This ability to produce sub-wavelength structures makes our techniques applicable to atomic beam lithography.
We introduce a new scheme for generating short-wavelength coherent broadband radiation with well-controlled spectral characteristics. It is based on shaping long-wavelength femtosecond pulse to coherently control atomic resonance-mediated (2+1) three-photon excitation to a broad far-from-resonance continuum. Here, the spectrum (central frequency and bandwidth) of deep-ultraviolet coherent broadband radiation generated in Na vapor is experimentally controlled by tuning the linear chirp we apply to the driving phase-shaped near-infrared femtosecond pulse. This is a first step in implementing the full scheme for producing shaped femtosecond pulses at wavelengths down-to the vacuum-ultraviolet range.