115 research outputs found
Observation of Collective-Emission-Induced Cooling inside an Optical Cavity
We report the observation of collective-emission-induced, velocity-dependent
light forces. One third of a falling sample containing 3 x 10^6 cesium atoms
illuminated by a horizontal standing wave is stopped by cooperatively emitting
light into a vertically oriented confocal resonator. We observe decelerations
up to 1500 m/s^2 and cooling to temperatures as low as 7 uK, well below the
free space Doppler limit. The measured forces substantially exceed those
predicted for a single two-level atom.Comment: 10 pages, 5 figure
On Two Models of the Light Pulse Delay in a Saturable Absorber
A comparative analysis of two approaches to description of the light
modulation pulse delay in a saturable absorber is presented. According to the
simplest model, the delay of the optical pulse is a result of distortion of its
shape due to absorption self-modulation in the nonlinear medium. The second
model of the effect, proposed at the beginning of our century, connects the
pulse delay with the so-called "slow light" resulting from the group velocity
reduction under conditions of the coherent population oscillations. It is shown
that all the known experimental data on the light pulse delay in saturable
absorbers can be comprehensively described in the framework of the simplest
model of saturable absorber and do not require invoking the effect of coherent
population oscillations with spectral hole-burning and anomalous modifications
of the light group velocity. It is concluded that the effect of group velocity
reduction under conditions of coherent population oscillations has not received
so far any experimental confirmation, and the assertions about real observation
of the "slow light" based on this mechanism are groundless.Comment: Regretfully, the journal version of the paper (in Optics and
Spectroscopy) appeared to be strongly corrupted due to ignorant editing. In
particular, "coherent population oscillations" (CPO) was replaced by
"population coherent oscillations" (PCO), "bleaching" - by "clearing", and
"bleachable absorber " - by "clearable absorber". Here we present original
version of the pape
Polarization instabilities in a two-photon laser
We describe the operating characteristics of a new type of quantum oscillator
that is based on a two-photon stimulated emission process. This two-photon
laser consists of spin-polarized and laser-driven K atoms placed in a
high-finesse transverse-mode-degenerate optical resonator, and produces a beam
with a power of 0.2 W at a wavelength of 770 nm. We observe
complex dynamical instabilities of the state of polarization of the two-photon
laser, which are made possible by the atomic Zeeman degeneracy. We conjecture
that the laser could emit polarization-entangled twin beams if this degeneracy
is lifted.Comment: Accepted by Physical Review Letters. REVTeX 4 pages, 4 EPS figure
Gas Dynamic Virtual Nozzle for Generation of Microscopic Droplet Streams
As shown by Ganan-Calvo and co-workers, a free liquid jet can be compressed
in iameter through gas-dynamic forces exerted by a co-flowing gas, obviating
the need for a solid nozzle to form a microscopic liquid jet and thereby
alleviating the clogging problems that plague conventional droplet sources of
small diameter. We describe in this paper a novel form of droplet beam source
based on this principle. The source is miniature, robust, dependable, easily
fabricated, and eminently suitable for delivery of microscopic liquid droplets,
including hydrated biological samples, into vacuum for analysis using vacuum
instrumentation. Monodisperse, single file droplet streams are generated by
triggering the device with a piezoelectric actuator. The device is essentially
immune to clogging
2020 American College of Rheumatology Guideline for the Management of Reproductive Health in Rheumatic and Musculoskeletal Diseases
Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/154675/1/art41191.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/154675/2/art41191_am.pd
Rapid assessment of nonlinear optical propagation effects in dielectrics
Ultrafast laser processing applications need fast approaches to assess the nonlinear propagation of the laser beam in order to predict the optimal range of processing parameters in a wide variety of cases. We develop here a method based on the simple monitoring of the nonlinear beam shaping against numerical prediction. The numerical code solves the nonlinear Schrödinger equation with nonlinear absorption under simplified conditions by employing a state-of-the art computationally efficient approach. By comparing with experimental results we can rapidly estimate the nonlinear refractive index and nonlinear absorption coefficients of the material. The validity of this approach has been tested in a variety of experiments where nonlinearities play a key role, like spatial soliton shaping or fs-laser waveguide writing. The approach provides excellent results for propagated power densities for which free carrier generation effects can be neglected. Above such a threshold, the peculiarities of the nonlinear propagation of elliptical beams enable acquiring an instantaneous picture of the deposition of energy inside the material realistic enough to estimate the effective nonlinear refractive index and nonlinear absorption coefficients that can be used for predicting the spatial distribution of energy deposition inside the material and controlling the beam in the writing process
Resilient emotionality and molecular compensation in mice lacking the oligodendrocyte-specific gene Cnp1
Altered oligodendrocyte structure and function is implicated in major psychiatric illnesses, including low cell number and reduced oligodendrocyte-specific gene expression in major depressive disorder (MDD). These features are also observed in the unpredictable chronic mild stress (UCMS) rodent model of the illness, suggesting that they are consequential to environmental precipitants; however, whether oligodendrocyte changes contribute causally to low emotionality is unknown. Focusing on 2′-3′-cyclic nucleotide 3′-phosphodiesterase (Cnp1), a crucial component of axoglial communication dysregulated in the amygdala of MDD subjects and UCMS-exposed mice, we show that altered oligodendrocyte integrity can have an unexpected functional role in affect regulation. Mice lacking Cnp1 (knockout, KO) displayed decreased anxiety- and depressive-like symptoms (i.e., low emotionality) compared with wild-type animals, a phenotypic difference that increased with age (3–9 months). This phenotype was accompanied by increased motor activity, but was evident before neurodegenerative-associated motor coordination deficits (⩽9–12 months). Notably, Cnp1KO mice were less vulnerable to developing a depressive-like syndrome after either UCMS or chronic corticosterone exposure. Cnp1KO mice also displayed reduced fear expression during extinction, despite normal amygdala c-Fos induction after acute stress, together implicating dysfunction of an amygdala-related neural network, and consistent with proposed mechanisms for stress resiliency. However, the Cnp1KO behavioral phenotype was also accompanied by massive upregulation of oligodendrocyte- and immune-related genes in the basolateral amygdala, suggesting an attempt at functional compensation. Together, we demonstrate that the lack of oligodendrocyte-specific Cnp1 leads to resilient emotionality. However, combined with substantial molecular changes and late-onset neurodegeneration, these results suggest the low Cnp1 seen in MDD may cause unsustainable and maladaptive molecular compensations contributing to the disease pathophysiology
Gene expression biomarkers of response to citalopram treatment in major depressive disorder
There is significant variability in antidepressant treatment outcome, with ∼30–40% of patients with major depressive disorder (MDD) not presenting with adequate response even following several trials. To identify potential biomarkers of response, we investigated peripheral gene expression patterns of response to antidepressant treatment in MDD. We did this using Affymetrix HG-U133 Plus2 microarrays in blood samples, from untreated individuals with MDD (N=63) ascertained at a community outpatient clinic, pre and post 8-week treatment with citalopram, and used a regression model to assess the impact of gene expression differences on antidepressant response. We carried out technical validation of significant probesets by quantitative reverse transcriptase PCR and conducted central nervous system follow-up of the most significant result in post-mortem brain samples from 15 subjects who died during a current MDD episode and 11 sudden-death controls. A total of 32 probesets were differentially expressed according to response to citalopram treatment following false discovery rate correction. Interferon regulatory factor 7 (IRF7) was the most significant differentially expressed gene and its expression was upregulated by citalopram treatment in individuals who responded to treatment. We found these results to be concordant with our observation of decreased expression of IRF7 in the prefrontal cortex of MDDs with negative toxicological evidence for antidepressant treatment at the time of death. These findings point to IRF7 as a gene of interest in studies investigating genomic factors associated with antidepressant response
Ultrafast laser micro-nano structuring of transparent materials with high aspect ratio
Ultrafast lasers are ideal tools to process transparent materials because
they spatially confine the deposition of laser energy within the material's
bulk via nonlinear photoionization processes. Nonlinear propagation and
filamentation were initially regarded as deleterious effects. But in the last
decade, they turned out to be benefits to control energy deposition over long
distances. These effects create very high aspect ratio structures which have
found a number of important applications, particularly for glass separation
with non-ablative techniques. This chapter reviews the developments of
in-volume ultrafast laser processing of transparent materials. We discuss the
basic physics of the processes, characterization means, filamentation of
Gaussian and Bessel beams and provide an overview of present applications
- …