Chirped Beams Research Articles

Pulse front distortions in focused spatially chirped beams

A numerical analysis of spatially chirped beams produced by single-pass grating pairs is presented. It is shown that focused pulse structures can deviate significantly relative to standard linear spatial chirp approximations depending upon the pulse bandwidth, the angle of incidence, and groove density of the gratings used.

Attosecond x-ray free-electron lasers utilizing an optical undulator in a self-selection regime

Accelerator-based x-ray free-electron lasers (XFELs) are the latest addition to the revolutionary tools of discovery for the 21st century. The two major components of an XFEL are an accelerator-produced electron beam and a magnetic undulator, which tend to be kilometer-scale long and expensive. A proof-of-principle demonstration of free-electron lasing at 27 nm using beams from compact laser wakefield accelerators was shown recently by using a magnetic undulator. However, scaling these concepts to x-ray wavelengths is far from straightforward as the requirements on the beam quality and jitters become much more stringent. Here, we present an ultracompact scheme to produce tens of attosecond x-ray pulses with several GW peak power utilizing a novel aspect of the FEL instability using a highly chirped, prebunched, and ultrabright tens of MeV electron beam from a plasma-based accelerator interacting with an optical undulator. The FEL resonant relation between the prebunched period and the energy selects resonant electrons automatically from the highly chirped beam which leads to a stable generation of attosecond x-ray pulses. Furthermore, two-color attosecond pulses with subfemtosecond separation can be produced by adjusting the energy distribution of the electron beam so that multiple FEL resonances occur at different locations within the beam. Such a tunable coherent attosecond x-ray sources may open up a new area of attosecond science enabled by x-ray attosecond pump/probe techniques. Published by the American Physical Society 2024

Radar Forward-Looking Imaging Based on Chirp Beam Scanning

Radar Forward-Looking Imaging Based on Chirp Beam Scanning

Ideal spatio-temporal pulse distribution for exawatt-scale lasers based on simultaneous chirped beam and chirped pulse amplification.

This paper presents the ideal spatio-temporal pulse structure that is required to produce exawatt-scale pulses based on simultaneous chirped beam and chirped pulse amplification in a Nd:Mixed-glass laser system. It is shown, that a 100 fs Fourier transform-limited pulse is created from a 20 ns duration stretched beam-pulse after propagating through an appropriate six-grating compressor arrangement. Quantitative results, from a ray-tracing model of the six-grating compressor, provide the detailed spatio-spectral and spatio-temporal pulse distributions of the stretched pulse along with the higher-order phase distortions compensated by this pulse compression scheme.

Time-stretch-based multidimensional line-scan microscopy

Time-stretch tomography imaging with ultrahigh frame rate is a breathtaking optical imaging method for acquiring large data sets for detection and classification of rare events. However, mechanical scans of both x and y dimensions are required to obtain tomography imaging. Here we introduce an ultrafast multidimensional time-stretch imaging method, only by one-dimensional scan, a multidimensional imaging can be obtained. An entire row of surface and depth information for a reflective sample is encoded onto the amplitude and frequency of a spatially dispersed ultrafast chirped beam, respectively. The present multidimensional line-scan microscopy approaches an ultrafast imaging system with micron level positioning accuracy in depth, three-dimensional surface information acquisition and tomography capability, which aimed at emerging applications for optical coherence tomography (OCT), light detection and ranging (LIDAR) and hyperspectral imaging.

The Nexawatt: A Strategy for Exawatt Peak Power Lasers Based on NIF and NIF-like Beam Lines

An exawatt-scale, short-pulse amplification architecture based upon a novel pulse compressor arrangement and amplification of long-duration chirped beam pulses is described. This architecture is capable of extracting the full, stored energy of a NIF or NIF-like beam line and in doing so produce from one beam line a near-diffraction-limited, laser pulse whose peak power would exceed 0.2 EW. The architecture is well suited to either low-f-number focusing or to multi-beam, dipole focusing concepts that in principle enable focused intensities in the range of 1026 W/cm2 or 5 orders of magnitude beyond that possible from present PW systems based on chirped pulse amplification.

Breakthroughs in Photonics 2014: Spatiotemporal Focusing: Advances and Applications

Exploiting the characteristics of spatially chirped ultrafast pulses has been an increasingly active area of research. In this paper, we review the developments in the past year of the microscopy, materials processing, and micromachining fields, where the spatiotemporal structure of these beams is important. We also summarize progress in theoretical and experimental work to better control and characterize spatially chirped beams.

Spatial chirp control of high-intensity 4D pulse focusing for laser-matter interactions

Spatial chirp can be manipulated to control the focusing conditions for materials processing. Our double-ABCD nonparaxial analysis helps to understand and exploit the mechanisms for intensity localization, pulse front tilt, and grating formation, and includes initial spectral phase and detuning of the wavelength crossing plane. We also present a novel method for creating high density, high intensity interference patterns with crossed beams that have no relative pulse front tilt. 1. Non-paraxial double ABCD tracing The properties of space-time focused beams are strongly dependent of the nature of the spatial overlap of the frequency components. The analysis of optical systems with spatial chirp is therefore critical both for understanding the unusual properties of these beams and for designing systems to exploit these properties for materials processing. In a recent paper, we developed an analytical approach to calculate the propagation of spatially chirped beams. A ray is traced that represents the central axis of the Gaussian beamlet for each frequency component. Since one form of the calculation is nonparaxial, the beamlet angles can be large and the calculation is valid over a wider range of conditions than direct Fresnel propagation. Our technique explains, for example, how the evolution of the beamlet radius of curvature leads to an axial variation of the spectral chirp through the focus, contributing to the axial intensity localization. It also allows the derivation of simple scaling properties of the beam, showing that the improvement of the localization over the confocal parameter of the focused beamlets depends primarily on the degree of spatial chirp, not on the initial pulse duration or the focal length.

Symmetrical fully-etched and chirped beam splitter based on a subwavelength binary blazed grating

A novel symmetrical chirped beam splitter based on a binary blazed grating is proposed, which adopts the fully-etched grating structure compatible with the current fabrication facilities for CMOS technology and convenient for integration and manufacture process. This structure can realize nearly equal-power splitting operation under the condition of TE polarization incidence. When the absolutely normal incidence occurs at the wavelength of 1580 nm, the coupling efficiencies of the left and the right branches are 43.627% and 43.753%, respectively. Moreover, this structure has the tolerances of 20 nm in etched depth and 3° in incident angle, which is rather convenient to manufacture facility.

Temporal shaping of ultrashort laser pulses by volume Bragg gratings

We propose a new method of temporal shaping of picosecond laser pulses using interference of chirped beams reflected from chirped volume Bragg gratings. This method is numerically simulated and experimentally tested. Quasi-rectangular picosecond pulses are experimentally obtained.

Frequency-Doubled Fiber Lasers for RF Spectrum Analysis in Spectral-Hole-Burning Media

We demonstrate an RF spectrum analyzer based on spectral-hole burning (SHB) that operates with unity probability of intercept and resolution under 100 kHz. An SHB crystal, which consists of rare-earth ions doped into a crystal host, records the power spectrum of an RF signal modulated onto an optical carrier as a series of spectral holes that persist for about 10 ms. While the crystal's homogeneous and inhomogeneous linewidths place the fundamental limits on resolution and bandwidth, respectively, the practical limits depend on the lasers used to interrogate the record stored in the crystal's absorption profile. Up to now, SHB spectrum analyzers have used chirped beams from externally modulated, stabilized lasers, which have linewidths of under 10 kHz but cannot chirp over much more than octave bandwidths, or directly modulated diode lasers, which can chirp over more than 20GHz but have linewidths of about 1 MHz. Switching to chirped fiber lasers, which have natural linewidths of under 2 kHz and chirping linewidths on the order of 10 kHz, produces a measurement with fine resolution without any laser stabilization. In addition, by chirping the fiber laser with a sufficiently fast piezo, the resulting chirp could extend over tens of gigahertz in under 10 ms, yielding both fine resolution and broad bandwidth without extraordinary stabilization schemes.

Dispersion properties of x-ray waveguides

We study the propagation of ultrashort pulses in x-ray waveguides (WGs) by addressing the problem of the temporal dispersion. Starting from basic equations, by means of numerical calculation we demonstrate that far from the absorption edges of the WGs the cladding's material dispersion is negligible. However, close to the absorption edge significant dispersion can take place. This behavior could in principle be exploited to manipulate incoming chirped beams. Moreover, using the two coherent beams produced by the WG in the second (and higher) order of resonance suggests the use of the WC as a dispersion-free beam splitter, which can facilitate x-ray pump-probe experiments in the femtosecond temporal range without the need for external sources.