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The interaction of intense (>1016 W/cm2), femtosecond laser pulses with metallic surfaces produces a high-densityplasma at the point of impact. This not only provides an opportunity for studying of high energy density physics, butalso facilitates the design of novel, micron-sized, femtosecond x-ray, electron and ion sources. There is tremendousinterest in such table-top pulsed x-ray sources for probing ultrafast reaction dynamics, micro-scale imaging andlithography. In an attempt to achieve maximal coupling of laser light to the solid target, we have shown that the useof nanostructured solid surfaces enhances the x-ray yield by a factor of 10 to 15 [1]. The enhanced x-ray productionis a consequence of the modification of local electric fields near nanoparticles [2]. Ion emission from nanostructuredmetallic surfaces excited by fs laser pulses is more complicated. Such surfaces produce twice as many ions as planarsurfaces in the moderate energy regime (16–75 keV), but their yield in the higher energy range (75–2000 keV) issubstantially lower [3,4].
Recently, we have observed a 40-50 fold enhancement in the hard x-ray emission (100–300 keV range) from Cunanorod arrays (as compared with an optically polished Cu surface) excited by 30 fs, 800 nm laser pulses at anintensity of 1016 W/cm2. The hot electrons which emit these x-rays show an 11-fold increase in temperature. Weshow that the higher yield arises from enhanced laser absorption due to the extremely high local electric fields aroundthe nanorod tips. Particle-in-cell plasma simulations reproduce these observations and provide pointers to furtheroptimization of the x-ray emission [5].
REFERENCES:
1. Metal nanoplasmas as bright sources of hard x-ray pulses; P P Rajeev, P Taneja, P Ayyub, A S Sandhu and G R Kumar: Phys. Rev. Lett. 90 (2003) 115002
2. Nanostructures, local fields and enhanced absorption in intense light–matter interaction; P P Rajeev, P Ayyub, S Bagchi, and G R Kumar, Optics Lett. 29 (2004) 2662
3. Hot ion generation from nanostructured surfaces under intense, femtosecond laser irradiation; S Bagchi, P Prem Kiran, M K Bhuyan, S Bose, P Ayyub, M Krishnamurthy and G R Kumar: App. Phys. Lett. 90 (2007) 141502
4. Fast ion beams from intense, femtosecond laser irradiated nanostructured surfaces; S Bagchi, P Prem Kiran, M K Bhuyan, S Bose, P Ayyub, M Krishnamurthy and G R Kumar: App. Phys. B 88 (2007) 167
5. Highly enhanced hard x-ray emission from oriented metal nanorod arrays excited by intense, femtosecond laser pulses; S Mondal, I Chakraborty, S Ahmad, D Carvalho, P Singh, A D Lad, V Narayanan, PAyyub, G R Kumar, J Zheng and Z M Sheng: Phys. Rev. B (2010) submitted
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