Hard x-ray scanning microscopy relies on small and intensive nanobeams. Refractive x-ray lenses are well suited to generate hard x-ray beams with lateral dimensions of 100 nm and below. The diffraction limited beam size of refractive x-ray lenses mainly depends on the focal length and the attenuation inside the lens material. The numerical aperture of refractive lenses scales with the inverse square root of the focal length until it reaches the critical angle of total reflection. We have used nanofocusing refractive x-ray lenses made of silicon to focus hard x-rays at 8 and 20 keV to (sub-)100 nm dimensions. Using ptychographic scanning coherent diffraction imaging we have characterized these nanobeams with high accuracy and sensitivity, measuring the full complex wave field in the focus. This gives access to the full caustic and aberrations of the x-ray optics.
A hard x-ray free-electron laser (XFEL) provides an x-ray source with an extraordinary high peak-brilliance, a time structure with extremely short pulses and with a large degree of coherence, opening the door to new scientific fields. Many XFEL experiments require the x-ray beam to be focused to nanometer dimensions or, at least, benefit from such a focused beam. A detailed knowledge about the illuminating beam helps to interpret the measurements or is even inevitable to make full use of the focused beam. In this paper we report on focusing an XFEL beam to a transverse size of 125nm and how we applied ptychographic imaging to measure the complex wavefield in the focal plane in terms of phase and amplitude. Propagating the wavefield back and forth we are able to reconstruct the full caustic of the beam, revealing aberrations of the nano-focusing optic. By this method we not only obtain the averaged illumination but also the wavefield of individual XFEL pulses.
Zone plates are circular diffraction gratings that can provide diffraction-limited nano-focusing of x-ray radiation. When
designing zone plates for X-ray Free Electron Laser (XFEL) sources special attention has to be made concerning the high
intensity of the sources. Absorption of x-rays in the zone material can lead to significant temperature increases in a single
pulse and potentially destroy the zone plate. The zone plate might also be damaged as a result of temperature build up
and/or temperature fluctuations on longer time scales. In this work we simulate the heat transfer in a zone plate on a
substrate as it is exposed to XFEL radiation. This is done in a Finite Element Method model where each new x-ray pulse
is treated as an instantaneous heat source and the temperature evolution between pulses is calculated by solving the heat
equation. We use this model to simulate different zone plate and substrate designs and source parameters. Results for
both the 8 keV source at LCLS and the 12.4 keV source at the European XFEL are presented. We simulate zone plates
made of high Z metals such as gold, tungsten and iridium as well as zone plates made of low Z materials such as
diamond. In the case of metal zone plates we investigate the influence of substrate material by comparing silicon and
diamond substrates. We also study the effect of different cooling temperatures and cooling schemes. The results give
valuable indications on the temperature behavior to expect and can serve as a basis for future experimental investigations
of zone plates exposed to XFEL radiation.
We present a technology for miniaturized, chip-based liquid dye lasers, which may be integrated with microfluidic networks and planar waveguides without addition of further process steps. The microfluidic dye lasers consist of a microfluidic channel with an embedded optical resonator. The lasers are operated with Rhodamine 6G laser dye dissolved in a suitable solvent, such as ethanol or ethylene glycol, and optically pumped at 532 nm with a pulsed, frequency doubled Nd:YAG laser. Both vertically and laterally emitting devices are realized. A vertically emitting Fabry-Perot microcavity laser is integrated with a microfluidic mixer, to demonstrate realtime wavelength tunability. Two major challenges of this technology are addressed: lasing threshold and fluidic handling. Low threshold, in-plane emission and integration with polymer waveguides and microfluidic networks is demonstrated with distributed feed-back lasers. The challenge of fluidic handling is addressed by hybridization with mini-dispensers, and by applying capillary filling of the laser devices.
We present a polymer lab-on-a-chip (LOC) microsystem with integrated optics, fabricated by thermal nanoimprint lithography (NIL) in a cyclic olefin copolymer, Topas from Ticona. The LOC contains microfluidic channels and mixers, an absorbance cell, optical waveguides, a microfluidic dye laser, and Fresnel lenses to couple light in and out of the waveguides. The polymer structure is embedded between two glass substrates. By this device we exploit the excellent chemical, mechanical and optical properties of Topas, and demonstrate the fabrication of millimeter to micrometer sized structures in one lithographic step. In addition, the NIL approach allows for addition of nanometer-scale features, limited only by the stamp fabrication. The silicon stamp for the imprint process is fabricated by standard UV-lithography and silicon deep reactive ion etching (DRIE). The sidewall roughness of the DRIE process is reduced to below 15 nm by thermal oxidation and subsequent oxide etching. Prior to imprint the stamp is coated with an anti-sticking coating from a perfluorodecyltrichlorosilane precursor by molecular vapor deposition. Topas, in our case grade 8007, dissolved in toluene is spin coated onto a SiO2 substrate. The imprint temperature is 200 °C, at an imprint force of 15000 N on a 4 inch wafer, imprint time is 5 min. Finally the imprinted structure is bonded to a pyrex wafer with a second layer of Topas in our case grade 9506. Bonding temperature is 70 °C, at a bonding force of 5000 N on a 4 inch wafer. Bonding time is 5 min.
We present a microcavity solid polymer dye laser based on a single
mode planar waveguide. The all-polymer device is self contained in
the photo definable polymer SU-8 and may therefore easily be
placed on any substrate, and integrated with polymer-based optical
or microfluidic systems. As the active medium for the laser we use
the commercially available laser dye Rhodamine 6G which is
incorporated into the SU-8 polymer matrix. The single mode slab
waveguide is formed by a 3-step spin coating deposition: a buffer
layer of un-doped SU-8, a core layer of SU-8 doped with Rhodamine,
and a cladding layer of un-doped SU-8. The refractive index
increases with Rhodamine concentration, and the difference between
the un-doped buffer and cladding layers and the doped core layer
is fine tuned to 0.001, allowing a large gain volume.
The integration of optical transducers is generally considered a key issue in the further development of lab-on-a-chip microsystems. We present a technology for the integration of miniaturized, polymer based lasers, with planar waveguides, microfluidic networks and substrates such as structured silicon. The flexibility of the polymer
patterning process, enables fabrication of laser light sources and other optical components such as waveguides, lenses and prisms, in the same lithographic process step on a polymer. The optically functionalised polymer layer can be overlaid on any reasonably flat substrate, such as electrically functionalised Silicon containing
photodiodes. This optical and microfluidic overlay, interfaces optically with the substrate through the polymer-substrate contact plane. Two types of integrable laser source devices are demonstrated: microfluidic- and solid polymer dye lasers. Both are based on laser resonators defined solely in the polymer layer. The polymer laser sources are optically pumped with an external laser, and emits light in the chip plane, suitable for coupling into chip waveguides. Integration of the light sources with polymer waveguides, micro-fluidic networks and photodiodes embedded in a Silicon substrate is shown in a device designed for measuring the time resolved absorption of two fluids mixed on-chip. The feasibility of three types of polymers is demonstrated: SU-8, PMMA and a cyclo-olefin co-polymer (COC) -- Topas. SU-8 is a negative tone photoresist, allowing patterning with conventional UV lithography. PMMA and Topas are thermoplasts, which are patterned by nanoimprint lithography (NIL).
The integration of optical transducers is generally considered a key issue in the further development of lab-on-a-chip Microsystems. We present a technology for miniaturized, polymer based lasers, suitable for integration with planar waveguides and microfluidic networks. The lasers rely on the commercial laser dye Rhodamine 6G as active medium, and the laser resonator is defined in a thin film of polymer on a low refractive index substrate. Two types of devices are demonstrated: solid and microfluidic polymer based dye lasers. In the microfluidic dye lasers, the laser dye is dissolved in a suitable solvent and flushed though a microfluidic channel, which has the laser resonator embedded. For solid state dye lasers, the laser dye is dissolved in the polymer forming the laser resonator. The miniaturized dye lasers are optically pumped by a frequency doubled, pulsed Nd:YAG laser (at 532 nm), and emit at wavelengths between 560 nm and 590 nm. The lasers emit in the plane of the chip, and the emitted light is coupled into planar polymer waveguides on the chip. The feasibility of three types of polymers is demonstrated: SU-8, PMMA and a cyclo-olefin co-polymer (COC) - Topas. SU-8 is a negative tone photoresist, allowing patterning with conventional UV lithography. PMMA and Topas are thermoplasts, which are patterned by nanoimprint lithography (NIL). The lasing wavelength of the microfluidic dye lasers can be coarse tuned over 30 nm by varying the concentration of laser dye, and fine tuned by varying the refractive index of the solvent. This is utilized to realize a tunable laser, by on-chip mixing of dye, and two solvents of different index of refraction. The lasers were also integrated with waveguides and microfluidic networks.