E.-B. Kley

Short-pulse optical parametric chirped-pulse amplification for the generation of high-power few-cycle pulses

We report ultrabroadband optical parametric chirped-pulse amplification (OPCPA) with an output pulse energy of up to 250 μJ from an OPCPA stage pumped by short pulses of ~100 fs duration at 395 nm wavelength. In order to generate ultrahigh-power pulses in the few-cycle regime, such a short-pulse-pumped OPCPA scheme appears to be a promising route, by virtue of its inherently advantageous features. Firstly, the stretching and compression fidelity as well as the pulse contrast are increased due to the short pump- and seed-pulse durations. Additionally, the higher pump powers allow for using thinner OPA crystals, thereby increasing the amplification bandwidth that will support even shorter pulse durations. We present experimental results where the effective bandwidth of the seed pulses was increased in the OPCPA process resulting in a shortened transform-limited pulse duration in addition to the energy gain. The amplified pulses from OPCPA have been compressed to the sub-10-fs, few-cycle range by using chirped mirrors. Scaling of this short-pulse-pumped OPCPA technique for few-cycle-pulse generation to the highest (TW–PW) power levels is also planned (Petawatt Field Synthesizer project at the Max-Planck-Institut fur Quantenoptik).

Optical characterization of ultrahigh diffraction efficiency gratings

We report on the optical characterization of an ultrahigh diffraction efficiency grating in a first-order Littrow configuration. The apparatus used was an optical cavity built from the grating under investigation and an additional high-reflection mirror. The measurement of the cavity finesse provided precise information about the gratings diffraction efficiency and its optical loss. We measured a finesse of 1580 from which we deduced a diffraction efficiency of (99.635+/-0.016)% and an overall optical loss due to scattering and absorption of just 0.185%. Such high-quality gratings, including the tool used for their characterization, might apply for future gravitational wave detectors. For example, the demonstrated cavity itself presents an all-reflective, low-loss Fabry-Perot resonator that might replace conventional arm cavities in advanced high-power Michelson interferometers.

New approach for antireflective fused silica surfaces by statistical nanostructures

In this work we present a new technique in order to create antireflective surfaces with the help of statistical nanostructures on fused silica. A specific plasma etching process was found to serve this purpose, as thereby nanostructures are created through self-masking. Under specific etching conditions the micro-contaminations create pillars on the surface with dimensions down to 20 nm, which act as an antireflective nanostructure. Those structures raise the transmission of fused silica in the wavelength range from 370 nm to 500 nm to more than 99.5% (both sides etched). Within the close UV range (from 200 nm up to 400 nm) the transmission can be raised by 4.8% to 97.1% on average.

Dispersion properties of photonic crystal waveguides with a low in-plane index contrast

We investigate dispersion properties of photonic crystal waveguides in a low-index material system. The modes above the light line, of a waveguide consisting of one row of missing holes (W1), exhibit high losses due to out-of-plane radiation. In contrast, the index-guided modes below the light line show moderate losses and we demonstrate both theoretically and experimentally that high dispersion is possible. Furthermore we investigate wider defect waveguides operated within the photonic band gap, where a mini-stopband with a very large suppression of transmission was found. The dispersion properties of these waveguides are discussed.

Power-recycled michelson interferometer with a 50/50 grating beam splitter

We designed and fabricated an all-reflective 50/50 beam splitter based on a dielectric grating. This beam splitter was used to set up a power-recycled Michelson interferometer with a finesse of about FPR ≈ 880. Aspects of the diffractive beam splitter as well as of the interferometer design are discussed.

Near-Field-Holography with a two dimensional phase mask for fabrication of two dimensional structures in a single exposure step

We present a technique for the fabrication of small period structures using a near field holography setup. Using a two-dimensionally structured phase mask, the creation of two-dimensional hole or dot arrays was possible with one single exposure step. In order to get a high contrast interference pattern, the mask parameters were optimized by rigorous calculation to achieve equal transmission efficiency in the respective diffraction orders. The mask generation was done by electron beam lithography and ion beam etching. We have made exposures with two different setups. The first setup is an exposure with normal incidence, where the interference of the four first diffraction orders is used. The second setup uses the zeroth and first diffraction order interference of a conical incident beam.

Refractive beam shaping elements

Summary form only given. The well-known advantages of refractive micro optical elements-high efficiency and low wavelength aberration-can be used for microlenses as well as in beam shaping applications, such as producing different top-hat intensity distributions.

Upper limit to the transverse to longitudinal motion coupling of a waveguide mirror

Waveguide mirrors possess nano-structured surfaces which can potentially provide a significant reduction in thermal noise over conventional dielectric mirrors. To avoid introducing additional phase noise from motion of the mirror transverse to the reflected light, however, they must possess a mechanism to suppress the phase effects associated with the incident light translating across the nano-structured surface. It has been shown that with carefully chosen parameters this additional phase noise can be suppressed. We present an experimental measurement of the coupling of transverse to longitudinal displacements in such a waveguide mirror designed for 1064 nm light. We place an upper limit on the level of measured transverse to longitudinal coupling of one part in seventeen thousand with 95% confidence, representing a significant improvement over a previously measured grating mirror.

Transmission properties of a free-standing lithium niobate photonic crystal waveguide

Transmission spectra of photonic crystal waveguides in freestanding lithium niobate membranes fabricated by means of ion-beam enhanced etching have been measured by scanning near-field optical microscopy show good agreement with 3DFDTD calculations.

Fabrication of high aspect ratio photonic crystal structures in lithium niobate

This article presents the ion beam etching technology for photonic crystal structures in lithium niobate. This new fabrication technique is able to create sub micrometer size elements in lithium niobate with a depth of up to 500 nm.