Towards cavity cooling of a molecular beam

Die Fähigkeit, kalte Moleküle mit hoher räumlicher Dichte herzustellen, eröffnet völlig neuartige Möglichkeiten in diversen Forschungsdisziplinen. Die direkte Anwendung der sehr erfolgreichen Kühl- und Fallen-Techniken für Atome auf Moleküle ist bisher nicht möglich. Nicht-resonantes Laserkühlen mit Hilfe optischer Resonatoren (Cavity Kühlen) eröffnet eine neue Perspektive kalte Moleküle herzustellen. Im Prinzip ist diese Methode auf jedes polarisierbare Teilchen anwendbar, welches das Kühllicht bei der gewählten Wellenlänge zwar streut, aber möglichst wenig absorbiert. Die Verwendung von nicht-resonantem Licht resultiert zum einen in einer \break schwachen Absorption, zum anderen in einer schwachen Kopplung zwischen \break Molekül und elektrischem Feld. Erreicht man jedoch eine kritische Laserleistung und molekulare Teilchendichte, so kann die schwache Molekül-Feld Kopplung ausgeglichen werden. Nichts desto weniger stellt das Cavity-Kühlen von Molkülen eine große Herausforderung dar. Bis heute konnte noch keine (Cavity-) Laser-Kühlmethode auf irgendein Molekül erfolgreich angewendet werden. Das Ziel dieses Experiments ist es, Moleküle zum allerersten Mal mit Hilfe von Licht zu kühlen. Durch Nutzung der vorteilhaften Eigenschaften eines Molekularstrahls, der verbesserten Molekül-Feld Kopplung in einem Resonator mit \break hochgradig entarteter Modenstruktur und der Verstärkung des Laser-Pumpfeldes in einer zweiten high-finesse Cavity ist dieses lang ersehnte Ziel durch diese Diplomarbeit in experimenteller Reichweite. Bisher wurde der gesamte Versuch geplant und aufgebaut. Die zwei high-finesse Resonatoren wurden hergestellt und charakterisiert, die Vakuum-Kammer, die darin enthaltene Molekül-Quelle und Detektion sind voll funtkionstüchtig und das optische Setup ist justiert. Somit können die ersten Messungen dieser neuartigen Kühlmethode für Moleküle beginnen.The ability to provide dense samples of cold molecules offers great opportunities in various different research fields. Unfortunately, the successful techniques available for cooling and trapping of atoms cannot be applied to molecules. Off-resonant cavity cooling is a very promising candidate to cool molecules even to ultracold temperatures. This method can be, in principle, applied to every polarizable particle, which is non-absorptive at the wavelength that is used. Using off-resonant light results in low absorption, but also in weak molecule-field coupling. Fortunately, above a critical laser intensity threshold the low coupling can be compensated by a high particle density. Nevertheless, the requirements for cavity cooling of molecules are challenging. Until now (cavity assisted) laser cooling of molecules has not been realized for any molecular species anywhere in the world. The aim of this experiment is to achieve the first optical cooling of molecules ever. By utilizing the features of a molecular beam, by enhancing the molecule-field coupling in a highly degenerate cavity mode structure and by amplifying the pump laser in a second high-finesse cavity this major goal has come into the reach based on the present Diploma thesis. By now the whole experiment has been designed and constructed. The high-finesse cavities have been manufactured and characterized, the vacuum chamber including the molecule source and detection are fully functional and the optical setup is aligned. Therefore the first experiments exploring this novel molecular cooling scheme are about to begin

Cavity-assisted manipulation of freely rotating silicon nanorods in high vacuum

Optical control of nanoscale objects has recently developed into a thriving field of research with far-reaching promises for precision measurements, fundamental quantum physics and studies on single-particle thermodynamics. Here, we demonstrate the optical manipulation of silicon nanorods in high vacuum. Initially, we sculpture these particles into a silicon substrate with a tailored geometry to facilitate their launch into high vacuum by laser-induced mechanical cleavage. We manipulate and trace their center-of-mass and rotational motion through the interaction with an intense intra-cavity field. Our experiments show optical forces on nanorotors three times stronger than on silicon nanospheres of the same mass. The optical torque experienced by the spinning rods will enable cooling of the rotational motion and torsional opto-mechanics in a dissipation-free environment.Comment: 8 page

Fetal eye movements on magnetic resonance imaging.

OBJECTIVES: Eye movements are the physical expression of upper fetal brainstem function. Our aim was to identify and differentiate specific types of fetal eye movement patterns using dynamic MRI sequences. Their occurrence as well as the presence of conjugated eyeball motion and consistently parallel eyeball position was systematically analyzed. METHODS: Dynamic SSFP sequences were acquired in 72 singleton fetuses (17-40 GW, three age groups [17-23 GW, 24-32 GW, 33-40 GW]). Fetal eye movements were evaluated according to a modified classification originally published by Birnholz (1981): Type 0: no eye movements; Type I: single transient deviations; Type Ia: fast deviation, slower reposition; Type Ib: fast deviation, fast reposition; Type II: single prolonged eye movements; Type III: complex sequences; and Type IV: nystagmoid. RESULTS: In 95.8% of fetuses, the evaluation of eye movements was possible using MRI, with a mean acquisition time of 70 seconds. Due to head motion, 4.2% of the fetuses and 20.1% of all dynamic SSFP sequences were excluded. Eye movements were observed in 45 fetuses (65.2%). Significant differences between the age groups were found for Type I (p = 0.03), Type Ia (p = 0.031), and Type IV eye movements (p = 0.033). Consistently parallel bulbs were found in 27.3-45%. CONCLUSIONS: In human fetuses, different eye movement patterns can be identified and described by MRI in utero. In addition to the originally classified eye movement patterns, a novel subtype has been observed, which apparently characterizes an important step in fetal brainstem development. We evaluated, for the first time, eyeball position in fetuses. Ultimately, the assessment of fetal eye movements by MRI yields the potential to identify early signs of brainstem dysfunction, as encountered in brain malformations such as Chiari II or molar tooth malformations

MR-based morphometry of the posterior fossa in fetuses with neural tube defects of the spine.

OBJECTIVES: In cases of "spina bifida," a detailed prenatal imaging assessment of the exact morphology of neural tube defects (NTD) is often limited. Due to the diverse clinical prognosis and prenatal treatment options, imaging parameters that support the prenatal differentiation between open and closed neural tube defects (ONTDs and CNTDs) are required. This fetal MR study aims to evaluate the clivus-supraocciput angle (CSA) and the maximum transverse diameter of the posterior fossa (TDPF) as morphometric parameters to aid in the reliable diagnosis of either ONTDs or CNTDs. METHODS: The TDPF and the CSA of 238 fetuses (20-37 GW, mean: 28.36 GW) with a normal central nervous system, 44 with ONTDS, and 13 with CNTDs (18-37 GW, mean: 24.3 GW) were retrospectively measured using T2-weighted 1.5 Tesla MR -sequences. RESULTS: Normal fetuses showed a significant increase in the TDPF (r = .956; p<.001) and CSA (r = .714; p<.001) with gestational age. In ONTDs the CSA was significantly smaller (p<.001) than in normal controls and CNTDs, whereas in CNTDs the CSA was not significantly smaller than in controls (p = .160). In both ONTDs and in CNTDs the TDPF was significantly different from controls (p<.001). CONCLUSIONS: The skull base morphology in fetuses with ONTDs differs significantly from cases with CNTDs and normal controls. This is the first study to show that the CSA changes during gestation and that it is a reliable imaging biomarker to distinguish between ONTDs and CNTDs, independent of the morphology of the spinal defect

Master Equation for the Motion of a Polarizable Particle in a Multimode Cavity

We derive a master equation for the motion of a polarizable particle weakly interacting with one or several strongly pumped cavity modes. We focus here on massive particles with complex internal structure such as large molecules and clusters, for which we assume a linear scalar polarizability mediating the particle-light interaction. The predicted friction and diffusion coefficients are in good agreement with former semiclassical calculations for atoms and small molecules in weakly pumped cavities, while the current rigorous quantum treatment and numerical assessment sheds a light on the feasibility of experiments that aim at optically manipulating beams of massive molecules with multimode cavities.Comment: 30 pages, 5 figure