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Femtosecond

About: Femtosecond is a research topic. Over the lifetime, 35106 publications have been published within this topic receiving 691405 citations. The topic is also known as: 1 E-15 s & fs.


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Journal ArticleDOI
TL;DR: In this paper, the authors examined the damage threshold as a function of polarization and concluded that the fundamental mechanism is self-terminated Zener-impact ionization, and that the deterministic and uniform damage threshold throughout the sample threshold stems from the uniform valence-electron density found in good quality optical materials.
Abstract: A remarkable feature of material damage induced by short-pulsed lasers is that the energy threshold becomes deterministic for sub-picosecond pulses. This effect, coupled with the advent of kHz and higher repetition rate chirped pulse amplification systems, has opened the field of femtosecond machining. Yet the mechanism of optical breakdown remains unclear. By examining the damage threshold as a function of polarization, we find that, contrary to established belief, multiphoton ionization plays an insignificant role in optical breakdown. The polarization independence, combined with the observed precise and uniform dielectric breakdown threshold even for nanometer-scale features, leads us to conclude that the fundamental mechanism is ‘self-terminated’ Zener-impact ionization, and that the deterministic and uniform damage threshold throughout the sample threshold stems from the uniform valence-electron density found in good-quality optical materials. By systematically exploring optical breakdown near threshold, we find that we can consistently machine features as small as 20 nm, demonstrating great promise for applications ranging from Micro ElectroMechanical Systems (MEMS) construction and microelectronics, to targeted disruption of cellular structures and genetic material.

224 citations

Journal ArticleDOI
TL;DR: Femtosecond transition-state spectroscopy (FTS) as discussed by the authors is a real-time technique for probing chemical reactions, which allows direct observation of a molecule in the process of falling apart or in the formation.
Abstract: When a chemical bond is broken in a direct dissociationreaction, the process is so rapid that it has generally been considered instantaneous and therefore unobservable. But the fragments formed interact with one another for times on the order of 10^(−13) s after the photon has been absorbed. On this time scale the system passes through intermediate transition configurations; the totality of such configurations have been, in the recent literature, designated as "transition states." Femtosecond transition‐state spectroscopy (FTS) is a real‐time technique for probing chemical reactions. It allows the direct observation of a molecule in the process of falling apart or in the process of formation. In this paper, the first in a series on femtosecond real‐time probing of reactions, we examine the technique in detail. The concept of FTS is explored, and the interrelationship between the dynamics of chemical reactions and molecular potential energy surfaces is considered. The experimental method, which requires the generation of spectrally tunable femtosecond optical pulses, is detailed. Illustrative results from FTS experiments for several elementary reactions are presented, and we describe methods for relating these results to the potential energy surface(s).

224 citations

Journal ArticleDOI
TL;DR: A simple model is presented to describe mode locking in a laser coupled to a nonlinear resonator, which reveals a new mechanism for pulse shortening and shows that shortening does not rely on dispersion in the auxiliary cavity.
Abstract: A simple model is presented to describe mode locking in a laser coupled to a nonlinear resonator. It reveals a new mechanism for pulse shortening and shows that shortening does not rely on dispersion in the auxiliary cavity. Experimental results are given to support the basic predictions of the model.

223 citations

Journal ArticleDOI
TL;DR: In this article, the authors demonstrate a simple, yet effective, method for the direct generation of mid-infrared optical frequency combs in the region from 2.5 to 4.0μm from a conventional and compact erbium-fibre-based femtosecond laser in the telecommunication band.
Abstract: Mid-infrared optical frequency combs are of significant interest for molecular spectroscopy due to the large absorption of molecular vibrational modes on the one hand, and the ability to implement superior comb-based spectroscopic modalities with increased speed, sensitivity and precision on the other hand. Here, we demonstrate a simple, yet effective, method for the direct generation of mid-infrared optical frequency combs in the region from 2.5 to 4.0 μm (that is, 2,500–4,000 cm−1), covering a large fraction of the functional group region, from a conventional and compact erbium-fibre-based femtosecond laser in the telecommunication band (that is, 1.55 μm). The wavelength conversion is based on dispersive wave generation within the supercontinuum process in an unprecedented large-cross-section silicon nitride (Si3N4) waveguide with the dispersion lithographically engineered. The long-wavelength dispersive wave can perform as a mid-infrared frequency comb, whose coherence is demonstrated via optical heterodyne measurements. Such an approach can be considered as an alternative option to mid-infrared frequency comb generation. Moreover, it has the potential to realize compact dual-comb spectrometers. The generated combs also have a fine teeth-spacing, making them suitable for gas-phase analysis. The direct generation of mid-infrared optical frequency combs in the region 2.5–4.0 μm from a 1.55-μm conventional and compact erbium-fibre-based femtosecond laser is demonstrated via coherent dispersive wave generation in silicon nitride nanophotonic waveguides.

223 citations

Journal ArticleDOI
TL;DR: In this article, the authors proposed the Fast CARS (femtosecond adaptive spectroscopic techniques for coherent anti-Stokes Raman spectroscopy) method.
Abstract: Airborne contaminants, e.g., bacterial spores, are usually analyzed by time-consuming microscopic, chemical, and biological assays. Current research into real-time laser spectroscopic detectors of such contaminants is based on e.g., resonance fluorescence. The present approach derives from recent experiments in which atoms and molecules are prepared by one (or more) coherent laser(s) and probed by another set of lasers. However, generating and using maximally coherent oscillation in macromolecules having an enormous number of degrees of freedom is challenging. In particular, the short dephasing times and rapid internal conversion rates are major obstacles. However, adiabatic fast passage techniques and the ability to generate combs of phase-coherent femtosecond pulses provide tools for the generation and utilization of maximal quantum coherence in large molecules and biopolymers. We call this technique FAST CARS (femtosecond adaptive spectroscopic techniques for coherent anti-Stokes Raman spectroscopy), and the present article proposes and analyses ways in which it could be used to rapidly identify preselected molecules in real time.

222 citations


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Performance
Metrics
No. of papers in the topic in previous years
YearPapers
20231,403
20223,116
20211,239
20201,571
20191,715
20181,651