Phased-array grating compression for high-energy chirped pulse amplification lasers

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.

Cross-fringe piston sensor for segmented optics

This paper presents a simple slit-mask-based sensing scheme that can be applied to a robust piston error sensor for segmented optical systems, even in space. Utilizing crossed fringes generated from multiple double-slit pairs, the sensor simultaneously detects multiple points in a segmented optical system in one shot. The experiments tested six pistons of a single-ring segmented mirror. The results showed measurement stability better than 15 nm in the range of 0-5 µm and absolute accuracy of λ/20. The theoretical perspective of applicability for larger piston measurement and N-ring segmented systems is also discussed, with simulation results for a two-ring system presented.

Effect of the measuring mirror surface shape error on ruled groove straightness and the grating diffraction wavefront

Measuring mirror requirements and their impact on groove errors are related to the error compensation strategy for a ruling engine. We analyze why the measuring mirror of the CIOMP-6 engine affects the groove straightness and the grating diffraction wavefront. We study a theoretical model of the relationship between the measuring mirror's surface shape error and the grating wavefront, propose a requirement for the measuring mirror surface shape error, and reprocess the measuring mirror. Comparative ruling experiments prove that the grating's wavefront quality at the diffraction order along the groove direction improved significantly after reprocessing of the measuring mirror.

Ruling engine using adjustable diamond and interferometric control for high-quality gratings and large echelles

A concept for position adjustment of the diamond in a ruling engine to enable nanoscale groove positioning is proposed. Based on this concept, we fabricate a diamond carriage, design an optical path, and propose an appropriate control method. Several high-quality gratings are ruled for spectrometer or interferometer applications. After implementation of the improvements, the maximum intensity of ghosts and scattered light of the echelle grating with 79 grooves/mm is reduced to half of that before the improvement, and the highest achievable groove density is increased from 6000 grooves/mm to 8000 grooves/mm. The grating ruling results indicate that the proposed concept and the related improvements to the engine significantly improve the accuracy of the CIOMP-6 ruling engine.

Method for calculation and analysis of the weights of grating mosaic errors

A method to calculate the weight of grating mosaic errors is proposed based on an analytical hierarchy process. An accurate mosaic error tolerance calculation formula is also presented that is useful for large-size grating fabrication by the mosaic method. The grating mosaic error weights and tolerances are analyzed for mosaic echelle gratings. The analytical error weight and tolerance results agree well with the experimental results. The mosaic grating's far-field intensity is 95.8%, which is higher than the 94% value from the simulation results.

Analysis and removal of five-dimensional mosaicking errors in mosaic grating

Combining the mathematical relationships between the grating wavefront and surfaces with the spatial relationships between the two grating wavefront, a mathematical model of the mosaicking errors is established to mosaic gratings. The five-dimensional mosaicking errors will respectively be calculated and then removed by the adjustment mechanisms. Mosaicking experiments are performed by using two gratings. First, by using zeroth order, the longitudinal offset is calculated and removed. Second, by using the diffraction order, the in-plane angle and grating spacing are calculated and removed, while the tip and tilt angles are calculated and removed. And then a mosaic grating is obtained.

Stable and near Fourier-transform-limit 30fs pulse compression with a tiled grating compressor scheme

The fabrication of meter-sized-gratings limits the rapid development of worldwide femtosecond ultra-intense lasers with 10PW or higher peak power, and the grating tiling method is an alternative to this problem. But the unreliability and complexity of the traditional grating tiling, which has already been widely used in picosecond Petawatt lasers, challenges its application in femtosecond ultra-intense lasers for wider bandwidth and more sensitive grating attitude. In this paper, we demonstrate an experiment to compress an 800nm centered nanosecond deep-chirped-pulse to around 30fs by an object-image-grating self-tiling compressor, to the best of our knowledge, which is the shortest pulse compressed by a tiled grating compressor. Both the compression pulse and the focal spot are stable and close to the theoretical limits. We believe it is a feasible solution to the grating-size-limited problem for recent femtosecond 10PW Ti:sapphire or OPCPA laser projects.

Littrow angle based autocollimation method for precision online monitoring three-dimensional angular drifts of chirped-pulse compression-gratings

A simple optical method for online precisely monitoring three-dimensional (3D) angular drifts of chirped-pulse compression-gratings in chirped-pulse amplification (CPA) lasers is proposed. Monitoring objects include all dimensional angular drifts of a grating, especially the grating groove in-plane-rotation. Monitoring contents contain direction and amount. And monitoring results are obtained by detecting the direction and the amount of 2D relative offsets of three focal spots formed by a ternary monitoring beam line. The theoretical model of the proposed method is set up using a matrix ray-tracing method, and a simplified monitoring equation is concluded based on numerical simulations. And the validity of this method is verified by a simple demonstration experiment. Besides, monitoring error and reliability discussion of the method are presented, as well.

Research on potential problems of object image grating self-tiling for applications in large aperture optical systems

Object image grating self-tiling reduces difficulties of obtaining an ideal grating tiling condition by eliminating three tiling errors in six within a tiled grating. However, this may bring two potential problems: higher requirements of adjustment accuracy and maintaining stability. To examine the application values of this grating tiling configuration, the performance of object image grating self-tiling and traditional grating tiling configurations on accuracy and stability are compared theoretically and experimentally. Adjustment accuracy requirements of two grating tiling configurations are calculated, a comparative experiment of long-term stabilities is demonstrated, and relevant theoretical simulation analyses are developed to explain the experiment results.

Object-image-grating self-tiling to achieve and maintain stable, near-ideal tiled grating conditions

We propose and demonstrate an object-image-grating self-tiling method for doubling the effective aperture of a grating by tiling it with its image to form an object-image-grating pair. With the aid of the object-image relation, the line-density variation, angular tip, and longitudinal piston errors within a tiled grating no longer exist. The method helps achieve and maintain a near-ideal tiled grating by using a simple far-field method. Because one tiled grating requires only one beam line, a single probe laser can be used for first-installation adjustments and long-term maintenance monitoring, with no wavelength or incident angle limitations.

Spectrally resolved and phase-sensitive far-field measurement for the coherent addition of laser pulses in a tiled grating compressor

We describe a method that can be used for the coherent addition of laser pulses. As different laser pulses are initially generated in a laser-pulse compressor equipped with a tiled grating, such a coherent addition is indispensable in order to maximize the intensity in the laser far field. We present measurements in this context where, up to now, an unavoidable difference in the grating constants between the phased gratings reduced the maximum achievable intensity. The method significantly facilitates the high-precision alignment of a tiled grating compressor and could also be used for a coherent addition of laser pulses.

Demonstration of large-aperture tiled-grating compressors for high-energy, petawatt-class, chirped-pulse amplification systems

Two large-aperture tiled-grating (1.5 m) compressors, each consisting of four sets of tiled-grating assemblies, have been built for the OMEGA EP high-energy petawatt-class laser system. The techniques used for tiling individual tiled-grating assemblies and for optimizing the overall performance of a tiled-grating compressor are described. Both compressors achieved subpicosecond pulse duration without tiling-induced temporal degradation. A ray-tracing model predicted that the static wavefront of the grating tiles dominated focal-spot degradations when submicroradian tiling accuracy is achieved. The tiled-grating compressors delivered a tighter focal spot compared with subaperture grating compressors with single central tiles.

Large-aperture grating tiling by interferometry for petawatt chirped-pulse-amplification systems

A tiled-grating assembly with three large-scale gratings is developed with real-time interferometric tiling control for the OMEGA EP Laser Facility. An automatic tiling method is achieved and used to tile a three-tile grating assembly with the overall wavefront reconstructed. Tiling-parameters sensitivity and focal-spot degradation from all combined tiling errors are analyzed for a pulse compressor composed of four such assemblies.

Tiled-grating compression of multiterawatt laser pulses

High-energy petawatt lasers require large diffraction gratings for pulse compression. As an alternative to meter-sized gratings, we demonstrate the capability of a tiled-grating system to compress multiterawatt subpicosecond laser pulses. Using a 100 TW-class Nd:glass chirped-pulse amplification laser facility, we report on the performance of a two-grating mosaic to compress high-energy pulses to 2.5 J, 450 fs (5.5 TW) in air with a beam size of 50 mm and energy transmission of 63%. Stability of the grating mosaic alignment was realized by use of an accurate nanopositioning optomechanical system. The output Gaussian spectrum was preserved from grating-gap spectral clipping and was free of modulation.