Search results for "Femtosecond"

Single crystal-like thin films of blue bronze

2021

Abstract Pulsed laser deposition technique was employed to grow thin films of K 0.3 M o O 3 on A l 2 O 3 (1-102) and S r T i O 3 (510) substrates. Structural and imaging characterization revealed good quality films with well oriented grains of few microns in length. Both non-selective (transport) and order-selective (femtosecond pump-probe spectroscopy) probes revealed charge density wave properties that are very close to those of the single crystals. The films exhibit metal-semiconductor phase transition in resistivity, pump-probe data show phase transition at the same temperature as the single crystal and the threshold for the photo-induced phase transition is approximately the same as in…

2020

Phytochrome proteins control the growth, reproduction, and photosynthesis of plants, fungi, and bacteria. Light is detected by a bilin cofactor, but it remains elusive how this leads to activation of the protein through structural changes. We present serial femtosecond X-ray crystallographic data of the chromophore-binding domains of a bacterial phytochrome at delay times of 1 ps and 10 ps after photoexcitation. The data reveal a twist of the D-ring, which leads to partial detachment of the chromophore from the protein. Unexpectedly, the conserved so-called pyrrole water is photodissociated from the chromophore, concomitant with movement of the A-ring and a key signaling aspartate. The chan…

2016

AbstractPhytochromes are a family of photoreceptors that control light responses of plants, fungi and bacteria. A sequence of structural changes, which is not yet fully understood, leads to activation of an output domain. Time-resolved serial femtosecond crystallography (SFX) can potentially shine light on these conformational changes. Here we report the room temperature crystal structure of the chromophore-binding domains of the Deinococcus radiodurans phytochrome at 2.1 Å resolution. The structure was obtained by serial femtosecond X-ray crystallography from microcrystals at an X-ray free electron laser. We find overall good agreement compared to a crystal structure at 1.35 Å resolution d…

Femtosecond structural dynamics drives the trans/cis isomerization in photoactive yellow protein

2016

Many biological processes depend on detecting and responding to light. The response is often mediated by a structural change in a protein that begins when absorption of a photon causes isomerization of a chromophore bound to the protein. Pande et al. used x-ray pulses emitted by a free electron laser source to conduct time-resolved serial femtosecond crystallography in the time range of 100 fs to 3 ms. This allowed for the real-time tracking of the trans-cis isomerization of the chromophore in photoactive yellow protein and the associated structural changes in the protein.Science, this issue p. 725A variety of organisms have evolved mechanisms to detect and respond to light, in which the re…

Ultrafast structural changes within a photosynthetic reaction centre

2021

Nature <London> / Physical science 589, 310 - 314 (2021). doi:10.1038/s41586-020-3000-7

Femtosecond Structural Dynamics of Proteins

2016

Proteins are the workhorses of living cells, providing essential functions such as structural support, signal transduction, enzymatic catalysis, transport and storage of small ligands. Atomic-resolution structures obtained with conventional X-ray crystallography show proteins essentially as static. In reality, however, proteins move and their motion is crucial for functioning. Although the structure and dynamics of proteins are intimately related, they are not equally well understood. A very large number of protein structures have been determined, but only a few studies have been able to monitor experimentally the dynamics of proteins in real time. In the last two decades, the availability …

Femtosecond up-conversion technique for probing the charge transfer in a P3HT : PCBM blend via photoluminescence quenching

2009

We report on an experimental study of the charge transfer dynamics in a P3HT : PCBM blend by means of a femtosecond fluorescence up-conversion technique. Using two-photon excitation we probe the exciton dynamics in P3HT and a P3HT : PCBM blend with a weight ratio of 1 : 1 at excitation densities of up to 6 × 1018 cm−3. In both samples we find strongly nonexponential decay traces compatible with (i) diffusion-limited exciton–exciton annihilation and (ii) diffusion-limited donor–acceptor charge transfer in the polymer blend. Additionally, our results indicate that in the P3HT : PCBM blend about 50% of the photogenerated excitons undergo a prompt charge transfer process on a time scale of abou…

Single versus double femtosecond laser pass for incomplete laser in situ keratomileusis flap in contralateral eyes: Visual and optical outcomes

2011

Purpose To evaluate visual acuity, refractive outcomes, and anterior corneal higher-order aberrations (HOAs) after myopic laser in situ keratomileusis (LASIK) with uneventful single femtosecond laser pass versus double pass performed for intraoperative suction loss. Setting Private refractive surgery center, Valencia, Spain. Design Cohort study. Methods After the LASIK flap was created with a single pass of an Intralase femtosecond laser in 1 eye and a double pass in the fellow eye, the ablation was performed with a Visx S2 laser. At 12 months, the refraction, uncorrected (UDVA) and corrected (CDVA) distance visual acuities, and anterior corneal HOAs were measured with 4.0 mm and 6.0 mm pup…

Femtosecond laser–assisted intrastromal corneal ring segment implantation for high astigmatism correction after penetrating keratoplasty

2013

PURPOSE: To assess the visual and refractive outcomes of femtosecond laser-assisted implanta- tion of Ferrara-type intrastromal corneal ring segments (ICRS) in post-penetrating keratoplasty (PKP) eyes. SETTING: Instituto OftalmolFernOviedo, Spain. DESIGN: Cohort study. METHODS: Patients with previous PKP had ICRS implantation after femtosecond laser tunnel creation. The uncorrected (UDVA) and corrected (CDVA) distance visual acuities and residual refractive errors were recorded before and 6 months after ICRS implantation. The power vector method was used to analyze refractive errors preoperatively and postoperatively. RESULTS: This study enrolled 32 eyes of 30 patients. The mean UDVA (Snell…

Effects of LASIK on Corneal Endothelium Using the 15-kHz IntraLase Femtosecond Laser

2011

PURPOSE: To assess the effects of LASIK with the 15-kHz IntraLase femtosecond laser on corneal endothelium. METHODS: In a prospective, single-center clinical trial, 138 patients (mean age: 32.0±7.1 years [range: 21 to 42 years]) underwent femtosecond LASIK for the correction of myopia −0.75 to −9.00 diopters (D) and cylinder up to 3.25 D. Patients were divided into two groups: contact lens group (n=76) and non-contact lens group (n=62). Pre- and 12-month postoperative specular microscopy of the central corneal endothelium was performed. The integrity of the central endothelium was assessed in terms of endothelial cell density and percentage of hexagonality. RESULTS: In the contact lens gro…