Compact x-ray microscope for the water window based on a high brightness laser plasma source

Herbert Legall ,H Sipma,J Luttmann,G Blobel,H Stiel,W Diete,W Sandner,M Höfer,U Wiesemann,M Wirtz,Dale Martz ,Torsten Feigl ,Per Takman ,Ulrich Vogt ,Hans M Hertz ,Hans-Dieter Hoffmann ,Peter Guttmann ,Gerd Schneider ,Dominik Esser ,Mårten Selin ,Stefan Rehbein ,Christian Seim ,Sergiy Yulin

doi:10.1364/oe.20.018362

Abstract

We present a laser plasma based x-ray microscope for the water window employing a high-average power laser system for plasma generation. At 90 W laser power a brightness of 7.4 x 10(11) photons/(s x sr x μm(2)) was measured for the nitrogen Lyα line emission at 2.478 nm. Using a multilayer condenser mirror with 0.3 % reflectivity 10(6) photons/(μm(2) x s) were obtained in the object plane. Microscopy performed at a laser power of 60 W resolves 40 nm lines with an exposure time of 60 s. The exposure time can be further reduced to 20 s by the use of new multilayer condenser optics and operating the laser at its full power of 130 W.

Highlights

Soft x-ray microscopy in the spectral range of the water window between 2.3 and 4.4 nm is ideally suited for the investigation of carbon containing structures in wet or frozen samples [1]
We present a laser plasma based x-ray microscope for the water window employing a high-average power laser system for plasma generation
A further reduction of recording times is already available by using a new multilayer condenser mirror with 0.6 % peak reflectivity

Summary

Introduction

Soft x-ray microscopy in the spectral range of the water window between 2.3 and 4.4 nm is ideally suited for the investigation of carbon containing structures in wet or frozen samples [1]. Micro zone plate based soft x-ray microscopes for investigations of 3-dimensional structures of biological specimens with nanometer resolution are operated with bright synchrotron radiation sources [4, 5]. The only worldwide existing soft X-ray fullfield microscope at an undulator beamline at BESSY II in Berlin employs a spherical grating monochromator beamline to illuminate an elliptically shaped mirror as condenser With this setup the spectral resolution is λ /Δλ = 10.000 and the condenser efficiency is 80% [6]. Note that the undulator TXM operates at an order of magnitude better spectral resolution with similar photon densities than the bending magnet TXM. A handful of high resolution zone plate based laboratory x-ray microscopes in the water window are in operation worldwide [13,14,15]. The characteristic parameters of the laboratory setup are shown and the performance of the table top x-ray microscope in the water window is demonstrated

Experimental arrangement

Results and discussion

Conclusions and future directions