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We demonstrate the feasibility of phase-contrast imaging with an ultrafast laser-based hard x-ray source. Hard x rays are generated during the interaction of a high-intensity femtosecond laser pulse (10 TW, 60 fs, 10 Hz) focused onto solid target in a very small spot (3 μm diam). Such a novel x-ray source has a number of advantages over other sources previously used for phase-contrast imaging: It is very compact and much cheaper than a synchrotron, it has higher power and better x-ray spectrum control than a microfocal x-ray tube, and it has much higher repetition rate than an x-pinch source. The Kα line at 17 keV produced using a solid Mo target, and the in-line imaging geometry have been utilized in this study. Phase-contrast images of test objects and biological samples have been realized. The characteristics of the images are the significant enhancement of interfaces due to an x-ray phase shift that reveal details that were hardly observable, or even undetectable, in absorption images and suppression of optically dense structures well defined in the absorption images. Our study indicates that the absorption and the phase-contrast images obtained with an ultrafast laser-based x-ray source provide complementary information about the imaged objects, thus enriching our arsenal of research tools for laboratory or clinic-based biomedical imaging. [ABSTRACT FROM AUTHOR]

Interaction of intense Ti:sapphire laser with solid targets has been studied experimentally by measuring hard x-ray and hot electron generation. Hard x-ray (8–100 keV) emission spectrum and Kα x-ray conversion efficiency (ηK) from plasma have been studied as a function of laser intensity (1017–1019 W/cm2), pulse duration (70–400)fs, and laser pulse fluence. For intensity I>1×1017 W/cm2, the Ag ηK increases to reach a maximum value of 2×10-5 at an intensity I=4×1018 W/cm2. Hot electron temperature (KTh) and ηK scaling laws have been studied as a function of the laser parameters. A stronger dependence of KTh and ηK as a function of the laser fluence than on pulse duration or laser intensity has been observed. The contribution of another nonlinear mechanism, besides resonance absorption, to hard x-ray enhancement has been demonstrated via hot electron angular distribution and particle-in-cell simulations. [ABSTRACT FROM AUTHOR]