High harmonic generation is a well-established optical method to produce coherent short-wavelength light in the ultraviolet and soft-X ray range. This nonlinear conversion process requires ultrashort pulse lasers of strong intensity exceeding the threshold of 10¹³ Wcm^-2 to ionize noble gas atoms. Chirped pulse amplification (CPA) is popularly used to increase the intensity power of a femtosecond laser produced from an oscillator. However, CPA requires long cavities for multi-staged power amplification, restricting its practical uses due to hardware bulkiness and fragility. Recently, we successfully exploited the phenomenon of localized surface plasmon resonance for high harmonic generation, which enables replacing CPA with a compact metallic nanostructure. Surface plasmon resonance induced in a well-designed nanostructure allows for intensity enhancement of the incident laser field more than 20 dB. For experimental validation, a 2D array of gold bowtie nanostructure was fabricated on a sapphire substrate by the focused-ion-beam process. By injection of argon and xenon gas atoms onto the bowtie nanostructure, high harmonics up to 21^st order were produced while the incident laser intensity remains at only 10¹¹ Wcm^-2. In conclusion, the approach of exploiting surface plasmons resonance offers an important advantage of hardware compactness in high harmonic generation.

Date Published: 2 September 2009
PDF: 11 pages
Proc. SPIE 7394, Plasmonics: Metallic Nanostructures and Their Optical Properties VII, 73940U (2 September 2009); doi: 10.1117/12.826645

Published in SPIE Proceedings Vol. 7394:
Plasmonics: Metallic Nanostructures and Their Optical Properties VII
Mark I. Stockman, Editor(s)