A Kerr polarization controller.

Kerr-effect-induced changes of the polarization state of light are well known in pulsed laser systems. An example is nonlinear polarization rotation, which is critical to the operation of many types of mode-locked lasers. Here, we demonstrate that the Kerr effect in a high-finesse Fabry-Pérot resonator can be utilized to control the polarization of a continuous wave laser. It is shown that a linearly-polarized input field is converted into a left- or right-circularly-polarized field, controlled via the optical power. The observations are explained by Kerr-nonlinearity induced symmetry breaking, which splits the resonance frequencies of degenerate modes with opposite polarization handedness in an otherwise symmetric resonator. The all-optical polarization control is demonstrated at threshold powers down to 7 mW. The physical principle of such Kerr effect-based polarization controllers is generic to high-Q Kerr-nonlinear resonators and could also be implemented in photonic integrated circuits. Beyond polarization control, the spontaneous symmetry breaking of polarization states could be used for polarization filters or highly sensitive polarization sensors when operating close to the symmetry-breaking point.

Evidence of high harmonics from echo-enabled harmonic generation for seeding x-ray free electron lasers.

Echo-enabled harmonic generation free electron lasers hold great promise for the generation of fully coherent radiation in x-ray wavelengths. Here we report the first evidence of high harmonics from the echo-enabled harmonic generation technique in the realistic scenario where the laser energy modulation is comparable to the beam slice energy spread. In this experiment, coherent radiation at the seventh harmonic of the second seed laser is generated when the energy modulation amplitude is about 2-3 times the slice energy spread. The experiment confirms the underlying physics of echo-enabled harmonic generation and may have a strong impact on emerging seeded x-ray free electron lasers that are capable of generating laserlike x rays which will advance many areas of science.

Demonstration of the echo-enabled harmonic generation technique for short-wavelength seeded free electron lasers.

We report the first experimental demonstration of the echo-enabled harmonic generation technique, which holds great promise for generation of high-power, fully coherent short-wavelength radiation. In this experiment, coherent radiation at the 3rd and 4th harmonics of the second seed laser is generated from the so-called beam echo effect. The experiment confirms the physics behind this technique and paves the way for applying the echo-enabled harmonic generation technique for seeded x-ray free electron lasers.

Achievement of ultralow emittance beam in the accelerator test facility damping ring.

For high luminosity in electron-positron linear colliders, it is essential to generate low vertical emittance beams. We report on the smallest vertical emittance achieved in single-bunch-mode operation of the Accelerator Test Facility, which satisfies the requirement of the x-band linear collider. The emittances were measured with a laser-wire beam-profile monitor installed in the damping ring. The bunch length and the momentum spread of the beam were also recorded under the same conditions. The smallest vertical rms emittance measured at low intensity is 4 pm at a beam energy of 1.3 GeV, which corresponds to the normalized emittance of 1.0x1.0(-8) m. It increases by a factor of 1.5 for a bunch intensity of 10(10) electrons. The measured data agreed to the calculation of intrabeam scattering within much better than a factor of 2.

Regional expression of murine intestinal immune cells in normal and isografted intestine.

The spatial organization and differentiation of the gut immune system was studied using immunohistochemistry from Embryonic Day 15 until adulthood. Leukocyte common antigen-positive cells were detected first, followed by macrophages, B, and then T lymphocytes increasing in number and intensity of staining until adulthood. The adult mouse displays regional localization of gut immune cells with highest expression in proximal intestine, decreasing distally to ileum with the fewest cells present in colon. The role of intestinal contents, bone marrow, and thymus on maturation of the gut immune system during development was studied using an isograft model: small intestine from neonatal mice were implanted subcutaneously into SCID mice and developed into morphologically normal intestine. Injected syngeneic mononuclear cells recirculated to the isografted intestine and SCID host intestine with the same regional expression as normal adult. This model is useful to define the mechanisms that establish and maintain cellular and regional differentiation of the normal gut immune system.

Functional analysis of cryopreserved veins. Preliminary report.

Functional comparisons of cryopreserved and fresh canine vein endothelium, smooth muscle, and connective tissue were performed. Morphometric analysis of saphenous vein endothelium revealed no significant loss of endothelial integrity as a result of cryopreservation. Endothelial cell culture revealed similar numbers of clonogenic intimal cells from cryopreserved and fresh saphenous, cephalic, and jugular veins. Smooth muscle function was assessed by measurement of the isometric force generated by vein rings in response to norepinephrine, serotonin, and potassium chloride. There was no significant difference in the dose responses of cryopreserved and fresh saphenous veins to the reagents tested. Similar results were obtained for the cephalic and jugular vein experiments with norepinephrine. The maximum tensions generated in response to norepinephrine were 52% of fresh control segments. Connective tissue function was assessed by quantitation of 3H-proline incorporation. The results indicate that cryopreserved veins retained approximately 43.5% of values of fresh vein collagen synthesis. Finally, eight cryopreserved cephalic vein autografts were placed as femoral artery grafts and were removed electively after 1 to 8 weeks. All grafts were patent. Both light and electron microscopy demonstrated that the cryopreserved veins remained intact in vivo and that arteriolization occurred as described for fresh autografts in the literature. In conclusion, cryopreserved veins retain much of their cellular and tissue functions on thawing. Transplantation of cryopreserved veins suggests that cryopreservation does not change the sequence of histologic events associated with the use of autologous fresh vein as an arterial substitute.