Experimental generation of high-contrast Talbot images with an ultrashort laser pulse G. Mı ´nguez-Vega a , O. Mendoza-Yero a , M. Ferna ´ndez-Alonso a , P. Andre ´s b , V. Climent a , J. Lancis a, * a GROC, Departament de Fı ´sica, Universitat Jaume I, 12080 Castello ´ , Spain b Departament d’O ` ptica, Universitat de Vale `ncia, 46100 Burjassot, Spain Received 5 June 2007; received in revised form 17 September 2007; accepted 21 September 2007 Abstract A femtosecond Ti:sapphire laser oscillator emitting pulses with 800 nm central wavelength, 10.9 fs pulse width, and 75 MHz repetition rate, combined with a dispersion-compensated diffractive system, was used to implement a large-area, high-contrast, broadband optical interference technique based on the Talbot effect. Chromatic artifacts associated with the huge spectrum of the optical source (approx- imately 150 nm) are compensated for with an air-separated hybrid diffractive–refractive lens doublet. The spatial resolution of the chro- matically compensated Talbot images under femtosecond illumination is nearly identical to that achieved under continuous wave monochromatic illumination. Furthermore, the temporal width of the signal at the Talbot planes is limited by the group-delay-dispersion coefficient which is shown to be small. High-contrast one-dimensional periodic structures of 96.1 lm spacing generated by Talbot dif- fractometry are experimentally demonstrated. Ó 2007 Elsevier B.V. All rights reserved. PACS: 42.79.Ci; 42.79.Dj; 42.62.b 1. Introduction Large-area patterning of periodic microstructures pro- vides a well-suited technique for the fabrication of bi- dimensional (2D) and three-dimensional (3D) photonic crystals (PhCs). Femtosecond laser interference (FLI) offers an elegant solution to this challenge [1]. FLI can pro- duce a periodically modulated light intensity distribution with a period in the order of the wavelength that is subse- quently transferred to a photoreactive material. Fabrica- tion of 3D PhCs, diffractive optical elements [2], and dot matrix, comb, and nanowire structures [3,4] by femtosec- ond laser ablation has been demonstrated. Both a refrac- tive beam splitter in conjunction with an optical delay line [5] and a diffractive beam splitter (DBS) with a confo- cal imaging system [6,7] have been employed in order to achieve the spatial and the temporal interference of the femtosecond pulses. Diffractive beam splitting leads to a simple optical setup and temporal overlap is achieved with- out any further adjustment. Coherent diffraction lithography (CDL) has emerged as a low-cost, large-area lithographic technique, compatible with precision multilevel alignment, and hence suitable for fabricating both 2D and 3D photonics crystals [8]. It is based on the self-imaging or Talbot effect [8]. In short, a mask, which contains a periodic pattern, generates posi- tive and negative self-images. A positive self-image is a Fresnel diffraction pattern whose amplitude distribution is identical to that of the object grating. On the other hand, the amplitude distribution of a negative self-image is iden- tical to that of the object except for the fact that is laterally displaced by half a period. It is well-known that under par- allel monochromatic illumination with angular frequency 0030-4018/$ - see front matter Ó 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.optcom.2007.09.058 * Corresponding author. Tel.: +34 964728055; fax: +34 964729218. E-mail address: lancis@fca.uji.es (J. Lancis). www.elsevier.com/locate/optcom Available online at www.sciencedirect.com Optics Communications 281 (2008) 374–379