Erez Gershgoren

Achieving λ/20 Resolution by One-Color Initiation and Deactivation of Polymerization

Subwavelength Patterning Microscopists have recently achieved fluorescence imaging at subwavelength resolution by focusing one beam of light in a halo around another beam, thereby quenching the glow of fluorescent dyes in all but the very center of the illuminated spot. Three studies have now adapted this approach to photolithography (see the Perspective by Perry). Andrew et al. (p. 917, published online 9 April) coated a photo-resist with molecules that, upon absorbing the ultraviolet etching beam, isomerized to a transparent layer but returned to the initially opaque form upon absorption of visible light. Applying an interference pattern with ultraviolet peaks superimposed on visible nodes restricted etching to narrow regions in the center of these nodes, yielding lines of subwavelength width. Scott et al. (p. 913, published online 9 April) used a central beam to activate polymerization initiators, while using a halo-shaped surrounding beam to trigger inhibitors that would halt polymerization. Li et al. (p. 910, published online 9 April) found that use of a different initiator molecule allowed both beams to share the same wavelength (800 nanometers), with a relatively weak quenching beam lagging a highly intense initiating beam slightly in time. Both the latter techniques produced three-dimensional features honed to subwavelength dimensions. Polymerization activated by a pulsed light beam was halted by a continuous beam of the same color in a surrounding halo. In conventional photolithography, diffraction limits the resolution to about one-quarter of the wavelength of the light used. We introduce an approach to photolithography in which multiphoton absorption of pulsed 800-nanometer (nm) light is used to initiate cross-linking in a polymer photoresist and one-photon absorption of continuous-wave 800-nm light is used simultaneously to deactivate the photopolymerization. By employing spatial phase-shaping of the deactivation beam, we demonstrate the fabrication of features with scalable resolution along the beam axis, down to a 40-nm minimum feature size. We anticipate application of this technique for the fabrication of diverse two- and three-dimensional structures with a feature size that is a small fraction of the wavelength of the light employed.

Nanoscale photothermal and photoacoustic transients probed with extreme ultraviolet radiation

We demonstrate the use of extreme ultraviolet (EUV) light for time-resolved measurements of the photothermal and photoacoustic response of materials. By using wavelengths that are 20× shorter than visible light, we demonstrate the potential for dramatically increased sensitivity and signal levels, in some cases by almost two orders of magnitude compared with visible light. This approach will enable probing of surface acoustic dynamics on nano-scale spatial dimensions of 50nm and below, using a small scale coherent EUV sources employing high-harmonic generation.

Use of a simple cavity geometry for low and high repetition rate modelocked Ti:sapphire lasers

We demonstrate a general procedure for varying the repetition rate of a modelocked Ti:sapphire laser using an asymmetric focusing geometry. Using this procedure, we have made an extended length cavity with a repetition rate of 45 MHz, and a reduced length cavity with a repetition rate of 275 MHz, each of which generates sub-20 fs pulses. This procedure allows the repetition rate of the laser to be more precisely tailored for a variety of applications without compromise in performance.

Probing of Thermo-Acoustic Transients in Materials Using EUV Radiation

The first application of EUV high-harmonic light to probe the nonlinear optical photoacoustic response of a sample is reported. This will enable measurements of thermal and acoustic transients in materials with sub-100nm resolution and wavelength.

Achieving resolution far beyond the diffraction limit with RAPID photolithography

A method to scale the resolution in photolithographic fabrication is introduced, in which one laser beam is used to initiate multiphoton absorption polymerization in a negative-tone photoresist while a second, phase-shaped laser beam is used to deactivate the polymerization. This approach allows for fabrication of polymeric nanostructures with λ/20 resolution.

Detection of thermal and acoustic transients in materials using heterodyned euv radiation

Nonlinear optical photoacoustic techniques have been extended from the visible to the EUV using high harmonics for the first time. This will enable measurements of thermal and acoustic transients in materials with sub-100 nm spatial resolution

Simplified setup for high-resolution spectroscopy using ultrashort pulses

Using a broadband femtosecond laser and simple optics, we demonstrate narrow-bandwidth tunable selective vibrational excitation in liquids. The resolution obtained is 80 times higher than the laser bandwidth-the highest obtained from a femtosecond laser to date.