Beat-frequency-resolved two-dimensional electronic spectroscopy: disentangling vibrational coherences in artificial fluorescent proteins with sub-10-fs visible laser pulses.

We perform a beat-frequency-resolved analysis for two-dimensional electronic spectroscopy using a high-speed and stable 2D electronic spectrometer and few-cycle visible laser pulses to disentangle the vibrational coherences in an artificial fluorescent protein. We develop a highly stable ultrashort light source that generates 5.3-fs visible pulses with a pulse energy of 4.7 µJ at a repetition rate of 10 kHz using multi-plate pulse compression and laser filamentation in a gas cell. The above-5.3-fs laser pulses together with a high-speed multichannel detector enable us to measure a series of 2D electronic spectra, which are resolved in terms of beat frequency related to vibrational coherence. We successfully extract the discrete vibrational peaks behind the inhomogeneous broadening in the absorption spectra and the vibrational quantum beats of the excited electronic state behind the strong incoherent population background in the typical 2D electronic spectra.

Real-time observation of the Woodward-Hoffmann rule for 1,3-cyclohexadiene by femtosecond soft X-ray transient absorption.

The stereochemistry of pericyclic reactions is explained by orbital symmetry conservation, referred to as the Woodward-Hoffmann (WH) rule. Although this rule has been verified using the structures of reactants and products, the temporal evolution of the orbital symmetry during the reaction has not been clarified. Herein, we used femtosecond soft X-ray transient absorption spectroscopy to elucidate the thermal pericyclic reaction of 1,3-cyclohexadiene (CHD) molecules, i.e., their isomerization to 1,3,5-hexatriene. In the present experimental scheme, the ring-opening reaction is driven by the thermal vibrational energy induced by photoexcitation to the Rydberg states at 6.2 eV and subsequent femtosecond relaxation to the ground state of CHD molecules. The direction of the ring opening, which can be conrotatory or disrotatory, was the primary focus, and the WH rule predicts the disrotatory pathway in the thermal process. We observed the shifts in K-edge absorption of the carbon atom from the 1s orbital to vacant molecular orbitals around 285 eV at a delay between 340 and 600 fs. Furthermore, a theoretical investigation predicts that the shifts depend on the molecular structures along the reaction pathways and the observed shifts in induced absorption are attributed to the structural change in the disrotatory pathway. This confirms that the orbital symmetry is dynamically conserved in the ring-opening reaction of CHD molecules as predicted using the WH rule.

100-mJ class, sub-two-cycle, carrier-envelope phase-stable dual-chirped optical parametric amplification.

Based on dual-chirped optical parametric amplification (DC-OPA) and type-I BiB3O6 (BiBO) crystals, the generation of >100 mJ, 10.4 fs, 10 Hz, carrier-envelope phase (CEP)-stable laser pulses, which are centered at 1.7 µm, was demonstrated producing a peak power of 10 TW. CEP-dependent high harmonic generation (HHG) was implemented to confirm the sub-two-cycle pulse duration and CEP stabilization of infrared (IR) laser pulses. As far as we know, the obtained pulse energy and peak power represented the highest values for sub-two-cycle CEP-stable IR optical parametric amplification. Additionally, the prospects of achieving high-energy water window isolated attosecond pulses (IAPs) via our developed laser source were discussed.

Optical parametric amplification of phase-stable terahertz-to-mid-infrared pulses studied in the time domain.

We report optical parametric amplification (OPA) of low-frequency infrared pulses in the intermediate region between terahertz (THz) frequency and mid-infrared (MIR), i.e., from 16.9 to 44.8 THz (6.7-17.8 µm). The 255-fs laser output of the Yb:KGW regenerative amplifier is compressed to 11-fs pulses using a multi-plate broadening scheme, which generates THz-to-MIR pulses with a spectrum extending to approximately 50 THz by intra-pulse differential frequency generation (DFG) in GaSe. The THz-to-MIR pulses are further amplified using a two-stage OPA in GaSe. The temporal dynamics and photocarrier effects during OPA are characterized in the time domain. Owing to the intra-pulse DFG, the long-term phase drift of the THz-to-MIR pulses after two-stage OPA is as small as 16 mrad during a 6-h operation without any active feedback. Our scheme using the intra-pulse DFG and post-amplification proposes a new route to intense THz-to-MIR light sources with extreme phase stability.

Generation and compression of an intense infrared white light continuum in YAG irradiated by picosecond pulses.

An intense white light (WL) continuum from 1600 to 2400 nm is generated in a 20-mm-long YAG irradiated by 1-ps, 1030-nm pulses. Long filamentation formed in the YAG is proven to be responsible for the enhancement of the longer-wavelength spectral part of the WL. The WL is compressed down to 24.6 fs ( 3.9 cycles at 1900 nm) after optical parametric chirped-pulse amplification in a lithium niobate crystal near degeneracy, confirming that its spectral phase is well behaved. The pulse compression experiment reveals that the group delay introduced in the WL generation process is dominated by the dispersion of YAG.

Broadband operation of a synchronously pumped optical parametric oscillator with a spatially dispersed beam.

We demonstrate the broadband operation of a synchronously pumped optical parametric oscillator (SPOPO) with a spatially dispersed beam and a fan-out type MgO-doped periodically poled LiTaO3 (MgO:PPLT). Spatial dispersion was generated using a glass prism placed in the SPOPO cavity. The poling period was designed to match the spatial dispersion and phase matching in MgO:PPLT, and the spectral dispersion in the cavity was compensated for using a fused silica plate, which had a negative dispersion at a signal wavelength of 1500-1600 nm. We succeeded in generating signal pulses with a pulse length of 81 fs, which was approximately 1/5 of the pump pulse length.

Generation of wavelength-tunable few-cycle pulses in the mid-infrared at repetition rates up to 10 kHz.

We demonstrate a compact and tunable mid-infrared light source that provides carrier-envelope-phase (CEP)-locked pulses at repetition rates from 500 Hz to 10 kHz. The seed pulses were generated by intra-pulse difference frequency mixing of the output of an Yb:KGW regenerative amplifier that had been spectrally broadened by continuum generation using multiple plates. Then, a two-stage optical parametric amplifier was used to obtain output energies of about 100 µJ/pulse for center wavelengths between 2.8 and 3.5 µm. Owing to the intense pulse energies, it was possible to compress the multi-cycle pulses down to two-cycle pulses using YAG and Si plates.

Investigation of inspiratory intercostal muscle activity in patients with spinal cord injury: a pilot study using electromyography, ultrasonography, and respiratory inductance plethysmography.

[Purpose] The respiratory function in patients with cervical spinal cord injury is influenced by inspiratory intercostal muscle function. However, inspiratory intercostal muscle activity has not been conclusively evaluated. We evaluated the inspiratory intercostal muscle activity in patients with cervical spinal cord injury by using inspiratory intercostal electromyography, respiratory inductance plethysmography, and ultrasonography. [Participants and Methods] Three patients with cervical spinal cord injury were assessed. The change in mean amplitude (rest vs. maximum inspiration) was calculated by using intercostal muscle electromyography. Changes in intercostal muscle thickness (resting expiration and maximum inspiration) were also evaluated on ultrasonography. The waveform was converted to spirometry ventilation with respiratory inductance plethysmography, and the waveform at the xiphoid was considered to determine the rib cage volume. Each index was compared with the inspiratory capacities in each case. [Results] Intercostal muscle electromyography failed to measure the notable myoelectric potential in all the patients. The rib cage volume was higher at higher inspiratory capacities. The changes in muscle thickness were not significantly different between the patients. [Conclusion] The rib cage volume (measured with inductance plethysmography) was greater in the patients with cervical spinal cord injury when inspiratory intercostal muscle activity was high. Respiratory inductance plethysmography can capture inspiratory intercostal muscle function in patients with cervical spinal cord injury.

Optical parametric amplification of carrier-envelope phase-stabilized mid-infrared pulses generated by intra-pulse difference frequency generation.

We report on a wavelength-tunable optical parametric amplifier (OPA) from 2.7 to 3.8 µm seeded with carrier-envelope phase (CEP) stabilized pulses generated by intra-pulse difference frequency generation (DFG) using a commercial Yb:KGW chirped-pulse amplifier. The Yb:KGW laser's output pulses are spectrally broadened in two-stage multi-plate pulse compression from 0.8 to 1.25 µm, which are compressed down to a sub-two-cycle duration of 6.5 fs using chirp mirrors. CEP-stabilized mid-infrared pulses are produced in intra-pulse DFG of the spectrally broaden pulses around 1.03 µm and parametrically amplified in KTiOAsO 4 crystals. The output energy and temporal duration of the OPA output pulses range from 31 to 56 µJ and from 102 to 203 fs, respectively. The root mean square value of their CEP errors is measured to be 101 mrad.

All-optical characterization of the two-dimensional waveform and the Gouy phase of an infrared pulse based on plasma fluorescence of gas.

The characterization of the temporal waveform of few-cycle laser pulses is an indispensable part in strong-field physics and attosecond science. Recently, a simple waveform-characterization technique called TIPTOE (tunneling ionization with a perturbation for the time-domain observation of an electric field) has been demonstrated for measuring linearly polarized few-cycle pulses. We theoretically and experimentally show that TIPTOE can be extended to resolve more characteristics of an optical waveform: the two-dimensional polarization and the Gouy phase. Based on the plasma fluorescence of a gaseous medium, we achieve all-optical and spatially resolved measurements of the waveform of an infrared pulse. This detection method enables the remote characterization of a waveform without the need to place an apparatus near the focal point of the laser beam. The proposed approach represents a simple and powerful method for conducting waveform diagnostics on few-cycle laser sources.

Nonlinear propagation effects in high harmonic generation in reflection and transmission from gallium arsenide.

High harmonic spectroscopy in solids is emerging as a new tool to investigate ultrafast electron dynamics in the presence of strong optical fields. However, the observed high harmonic spectra do not usually reflect the microscopic origin of high harmonic generation (HHG) because of nonlinear and/or linear propagation effects. Here, we systematically investigate the HHG in reflection and transmission from gallium arsenide exposed to intense mid-infrared optical pulses. In transmission geometry, we find that the properties of high harmonics are drastically changed by nonlinear effects during the propagation of even tens of micrometers. Especially, the nonlinear absorption and/or nonlinearly induced ellipticity of the drive pulses as well as a cascade nonlinear mixing significantly alter the high harmonic signals in the case of the transmission geometry, making an extraction of the microscopic electron dynamics of gallium arsenide difficult. On the contrary, in reflection geometry, we obtain HHG spectra that are free from propagation effects, opening a general approach for high harmonic spectroscopy.

Generation of sub-two-cycle CEP-stable optical pulses at 3.5 µm from a KTA-based optical parametric amplifier with multiple-plate compression.

We demonstrate the generation of 21 fs (1.8 optical cycle), 45-µJ, carrier-envelope phase (CEP)-stable optical pulses with an octave-spanning spectrum from 2.2 to 4.9 µm. Multi-cycle output pulses (120 fs, 149 µJ, 3.5 µm, and 300 Hz) from a KTA-based optical parametric amplifier are compressed down to the sub-two-cycle regime using YAG and Si plates. The single-shot CEP stability of the compressed pulses is measured to be 283 mrad for 500 s. This robust and compact scheme realizes a field strength of 282 MV/cm with f/11 focusing, opening a new regime of attosecond strong-field physics in solids.

Polarization-Resolved Study of High Harmonics from Bulk Semiconductors.

The polarization property of high harmonics from gallium selenide is investigated using linearly polarized midinfrared laser pulses. With a high electric field, the perpendicular polarization component of the odd harmonics emerges, which is not present with a low electric field and cannot be explained by the perturbative nonlinear optics. A two-dimensional single-band model is developed to show that the anisotropic curvature of an energy band of solids, which is pronounced in an outer part of the Brillouin zone, induces the generation of the perpendicular odd harmonics. This model is validated by three-dimensional quantum mechanical simulations, which reproduce the orientation dependence of the odd-order harmonics. The quantum mechanical simulations also reveal that the odd- and even-order harmonics are produced predominantly by the intraband current and interband polarization, respectively. These experimental and theoretical demonstrations clearly show a strong link between the band structure of a solid and the polarization property of the odd-order harmonics.

Oxygen cost of thoracic and diaphragmatic breathing during hyperventilation in healthy males.

[Purpose] It is unclear whether diaphragmatic breathing (DB) results in lower respiratory muscle oxygen consumption during dynamic exercise. The purpose of this study was to compare oxygen consumption in the respiratory muscles (VO2rm) with thoracic breathing (TB) and with DB, in healthy males during hyperventilation. [Subjects and Methods] Ten healthy men participated in this study. The subjects sat on a chair with the backrest reclined at an angle of 60 degrees. Respiratory parameters were measured breath by breath, using an expired gas analyzer. Oxygen consumption was measured for three minutes during quiet breathing. Measurements during TB and DB were performed for one minute each, after connecting a rebreather loading device. The breathing pattern was analyzed by inductance plethysmography, using transducer bands placed over the chest and abdomen that recorded thoracoabdominal movements. [Results] Both ΔVO2/body weight and VO2rm decreased significantly with DB when compared to that with TB, during hyperventilation. [Conclusion] DB results in less respiratory muscle oxygen consumption, even during dynamic exercise.

Generation of carrier-envelope phase-stable mid-infrared pulses via dual-wavelength optical parametric amplification.

Carrier-envelope phase-stable mid-infrared pulses spanning from 5 µm to 11 µm with a pulse energy of 5 µJ were produced by difference frequency generation of two-color near-infrared pulses that were produced in a novel inline optical parametric amplifier. The mid-infrared electric waveform was characterized by electro-optic sampling using 6.5-fs pulses at 620 nm.

Wavefront analysis of high-efficiency, large-scale, thin transmission gratings.

Large-scale (180 × 60 × 1 mm(3)) transmission gratings with groove densities of 1250 and 1740 lines/mm have been developed, resulting in diffraction efficiencies above 95%. The throughput of a folded pulse compressor with two large-scale transmission gratings was approximately 80% in a 20-fs Ti:sapphire chirped-pulse amplification (CPA) laser. The parabolic bending of the transmission grating due to anti-reflection (AR) coating was minimized to 2.9 λ at 633 nm by improving the evaporation process. By a simple analysis, we explain why this level of bending does not induce a wavefront distortion through the transmission grating near the Littrow condition while the wavefront from a reflection grating is distorted to nearly twice the bending of the grating. The calculation based on the measured bending shows that both the group delay difference relative to the ideally flat grating from 750 to 850 nm and the spatial pulse front distortion over a 60-mm-diameter input beam are negligible, even when the dispersive beam covers ~140 mm on the grating. The spatial pulse front distortion measured after the compressor was less than the measurement limit (1.5 fs) for a 20-mm-diameter beam, where the beam size in the dispersive direction on the grating was 85 mm.

Rib cage contributions to inspiratory capacity in patients with cervical spinal cord injury.

Background: Cervical spinal cord injury (CSI) often leads to impaired respiratory function, affecting the overall well-being of patients. This study aimed to investigate the influence of rib cage motion on inspiratory capacity in CSI patients. Methods: We conducted a study with 11 CSI patients, utilising respiratory inductance plethysmography (RIP). We measured ventilatory volume by spirometry concurrently with RIP. Participants were instructed to perform maximal inspiratory efforts. Inspiratory capacity (IC) was calculated from spirometry waveforms. We converted the respiratory waveforms of the chest and abdomen into inspiratory volume measured by a spirometer. The inspiratory volume measured by the chest sensor was defined as VRIP-rib cage (VRIP-rc), and the inspiratory volume measured by the abdominal sensor was defined as VRIP-abdomen (VRIP-ab). Subsequently, the relationships of IC with VRIP-rc and VRIPab were assessed. Results: The mean IC was 1.828 ± 0.459 L, with the mean VRIP-rc at 1.343 ± 0.568 L and the mean VRIP-ab at 0.485 ± 0.427 L. A significant correlation was observed between IC and VRIP-rc (r = 0.67, p = 0.02), indicating that rib cage motion significantly influences IC in CSI patients. Conclusion: This study highlights the importance of rib cage motion in assessing inspiratory capacity in patients with CSI.

MicroRNA-1826 directly targets beta-catenin (CTNNB1) and MEK1 (MAP2K1) in VHL-inactivated renal cancer.

The aim of this project is to identify new therapeutic microRNAs (miRNAs) for von Hippel-Lindau (VHL)-inactivated renal cancer cells. We initially identified several potential miRNAs targeting CTNNB1 and MEK1 using several targets scan algorithms. Only miR-1826 was found to target CTNNB1 and MEK1. Therefore, we focused on miRNA-1826 and performed 3' untranslated region (UTR) luciferase assay, functional analyses and association study between miR-1826 expression and renal cancer patient outcomes. miR-1826 expression was significantly lower in renal cancer tissues compared with non-neoplastic areas and lower expression was significantly associated with overall shorter survival and earlier recurrence after radical nephrectomy. Following miR-1826 transfection, 3' UTR luciferase activity and protein expression of beta-catenin and MEK1 were significantly downregulated in renal cancer cells. Introduction of miR-1826 also inhibited renal cancer cell proliferation, invasion and migration. Additionally, miR-1826 promoted apoptosis and G(1) arrest in VHL-inactivated renal cancer cells. Knockdowns of CTNNB1 and MEK1 by small interfering RNAs reproduced the tumor-suppressive effect of miR-1826. Our data suggest that the miR-1826 plays an important role as a tumor suppressor by downregulating beta-catenin and MEK1 in VHL-inactivated renal cancers.

Generation of soft x-ray and water window harmonics using a few-cycle, phase-locked, optical parametric chirped-pulse amplifier.

Multimillijoule, few-cycle, carrier-envelope-phase (CEP)-locked, near-IR pulses at 750 nm from an optical parametric chirped-pulse amplifier are applied to the generation of CEP-dependent, soft x-ray high harmonics around the boron K-edge at 188 eV. The dependence on the CEP manifests the phase coherence of high harmonics preserved in the highest-photon energy ever reported. Multimillijoule optical pulses also allow the extension of the cutoff energy up to 325 eV, exceeding the carbon K-edge of the water window. However, in this spectral range, the CEP dependence of harmonic spectra is not observed, suggesting the degradation of temporal coherence due to the heavy ionization of helium atoms.

Effects of breathing control using visual feedback of thoracoabdominal movement on aerobic exercise.

PURPOSE: To clarify whether voluntary respiratory movement control strategy is sustainable during exercise and to determine its effect on aerobic exercise. MATERIAL AND METHODS: Ten healthy men were enrolled in this study. We developed a device that can convert information on thoracoabdominal changes from an inductance plethysmograph and display the Konno-Mead diagram on the monitor in real time for each breath. On the first day, an incremental load test (ILT) was performed under two conditions. On the second day, a constant load test (CLT) was performed under two conditions using the load 1 min before the anaerobic threshold (AT). RESULTS: In the ILT, a significant prolongation of AT time was observed with voluntary respiratory movement control. In the CLT, carbon dioxide excretion showed no significant interaction, but the gas exchange ratio did. CONCLUSION: Voluntary respiratory movement control using a combination of chest band and visual feedback of thoracoabdominal movements may be a respiratory strategy to enhance aerobic exercise.