For reducing both extreme ultraviolet attosecond pulses energy loss in the focusing reflection process and measurement error caused by pulse focusing aberration, as well as improving the operability of pulse spectroscopy monitoring, a combined focusing and flat-field spectrometer analysis system for attosecond pulse is proposed and designed through step-by-step performance optimization. The focusing and spectrum-analyzing components are gold- coated grazing incidence to roidal mirror and grazing incidence concave focusing grating, respectively. The characteristic parameters of the system are given in details. The system proposed can find application in research platform of attosecond spectroscopy using high energy short attosecond pulse as basic probe tool.
With the mature of carrier-envelop phase (CEP) stabilized few cycle laser technology, the strong field optics is now shifting from the stage of perturbative to extreme (or nonperturbative) nonlinear optical mechanism, of which one of the most exciting achievements is the establishment of new light source―single isolated attosecond laser pulse in extreme ultraviolet (XUV) or even X-ray electromagnetic spectrum based on strong field high-order harmonic generation (1 attosecond = 1as = 10−18 s) [
In this paper, we proposed a combined focusing and flat-field spectrum-ana- lyzing system based on a grazing incidence toroidal focusing mirror and toroidal concave grating. The toroidal instead of spherical mirror helps reduce the reflection energy loss and suppress the focusing aberrations. The simulated results related are given, together with the characteristic system parameters.
The proposed system is shown in
The toriodal mirror used is gold-coated from ARW Optical Corporation, of which the two characteristic radiusas shown in
Rh = 3230 mm, with both radius tolerance smaller than ±1% and surface smooth accuracy better than l/2@632.8 nm. The focus characteristics of toroidal mirror can be decomposed into that in both meridian and sagittal planes, shown in
To eliminate the focus astigmatism, rh = rv must be met. Thus one can get the characteristic incidence angle of
As for the grating, its curvature radius is Rg = 13,450 mm and the line density distribution in its concave surface is as following:
Here, d0 = 1200 l/mm refers to central grating linear density, w is the perpendicular distance from given grating line midpoint to the grating surface vertex normal, d1, d2, and d3arecontrol parameters,d1 = −3.546 mm−2, d2 = 8.656 ´ 10−3 mm−3, d3 = −2.209 ´ 10−5 mm−4. The grazing incidence flat-field grating spectrometer is shown in
For a grazing incidence concave grating, rg(l) and β(l) meet the following conditions:
where
This material presents a combined focusing and spectrum-analysis system for XUV attosecond pulse, in which the focusing and spectrum-analyzing components are gold-coated grazing incidence toroidal mirror and grazing incidence concave focusing grating, respectively. It possesses the feature of reducing both attosecond pulses energy loss in the focusing reflection process and measurement error caused by attosecond pulse focusing aberration measurement, as well as improving the operability of attosecond pulse spectroscopy monitoring. Through step-by-step performance optimization, the structure and characteristic parameters are given in details. The system proposed can find application in research platform of attosecond spectroscopy using high energy short attosecond pulse as basic probe tool. The simulated results are given, together with the characteristic system parameters.
Y. K. thanks the National Natural Science Foundation of China (Grant No. 11505289). C. W. thanks the National Natural Science Foundation of China (Grant No. 11675258) and the project support from Ministry of Personnel of Shaanxi Province.
Kang, Y.F. and Wang, C. (2017) Combined Focusing and Flat-Field Spectrometer System for Extreme Ultraviolet Pulse. Optics and Photonics Jour- nal, 7, 14-19. https://doi.org/10.4236/opj.2017.78B003