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A 2D spacer (2TEAI) has been synthesized and deposited on PVSCs, which led to a significant increase in the efficiency from 21.7% to 23.6%, as well as 21.32% for the up-scaled device (2.25 cm2).

Hydrogen bonding plays an essential role in biological processes by stabilizing proteins and lipid structures as well as controlling the speed of enzyme catalyzed reactions. Dimethyl sulfoxide-water (DMSO-H2O) solution serves as a classical model system by which the direct and indirect effects of hydrogen bonding between water hydrogens and the sulfoxide functional group can be explored. The complex transition from self-bonding to heterogeneous bonding is important, and multiple spectroscopic approaches are needed to provide a detailed assessment of those interactions. In this report, for the first time, hyper-Raman scattering was successfully employed to investigate molecular interactions in DMSO-H2O system. We measured the improper blueshift of the C–S and C–H stretching modes of DMSO caused by partial charge transfer and enhanced bond polarization. By detecting differences in the frequency shifts of C–S and C–H modes for low DMSO concentrations (

Floquet modulation has been widely used in optical lattices for coherent control of quantum gases, in particular for synthesizing artificial gauge fields and simulating topological matters. However, such modulation induces heating which can overwhelm the signal of quantum dynamics in ultracold atoms. Here we report that the thermal motion, instead of being a noise source, provides a new control knob in Floquet-modulated superradiance lattices, which are momentum-space tight-binding lattices of collectively excited states of atoms. The Doppler shifts combined with Floquet modulation provide effective forces along arbitrary directions in a lattice in frequency and momentum dimensions. Dynamic localization, dynamic delocalization and chiral edge currents can be simultaneously observed from a single transport spectrum of superradiance lattices in thermal atoms. Our work paves a way for simulating Floquet topological matters in room-temperature atoms and facilitates their applications in photonic devices., Comment: 7 pages, 4 figures

Hydrogen bonding plays an essential role in biological processes. In this report we apply hyper-Raman scattering spectroscopy to probe the effects of the alkyl groups on hydrogen bonding in mixtures of DMSO-methanol. We characterize the dependence of hyper-Raman spectra on concentration and observe suppression of the hyper-Raman responses of the methanol alkyl group at intermediate concentrations. In addition, small frequency shifts in the vibrational frequencies of DMSO and methanol were detected. These results provide new insights into the nature of the hydrogen bonding in solution and into the details of the hydrogen bond’s interaction with the alkyl groups.

Considering the thermodynamical fluid mechanics in the gain medium and laser kinetic processes, a three-dimensional theoretical model of an exciplex-pumped Cs vapor laser with longitudinal and transverse gas flow is established. The slope efficiency of laser calculated by the model shows good agreement with the experimental data. The comprehensive three-dimensional distribution of temperature and particle density of Cs is depicted. The influence of pump intensity, wall temperature, and fluid velocity on the laser output performance is also simulated and analyzed in detail, suggesting that a higher wall temperature can guarantee a higher output laser power while causing a more significant heat accumulation in the cell. Compared with longitudinal gas flow, the transverse flow can improve the output laser power by effectively removing the generated heat accumulation and alleviating the temperature gradient in the cell.

By measuring the decoherence times and peak shifts of CC vibration of acetone, we experimentally demonstrated a novel coherent time-resolved Infrared spectroscopy technique to study hydrogen bond in acetone and water mixture.

A theoretical model is established to describe the kinetic processes and laser mechanism for a nanosecond-pulse exciplex pumped Cs vapor laser (XPCsL). A new simulation method is proposed to solve a set of non-stationary rate equations considering high energy levels and the results of simulation are consistent with the experimental data. The effects of cell temperature, pump energy and buffer gas on the output laser pulses are presented and analyzed in detail, which reveal the unique properties of nanosecond-pulse XPCsL.

The optical activity of Raman scattering provides insight into the absolute configuration and conformation of chiral molecules. Applications of Raman optical activity (ROA) are limited by long integration times due to a relatively low sensitivity of the scattered light to chirality (typically 10-3 to 10-5). We apply ROA techniques to hyper-Raman scattering using incident circularly polarized light and a right-angle scattering geometry. We explore the sensitivity of hyper- Raman scattering to chirality as compared to spontaneous Raman optical activity. Using the excitation wavelength at around 532 nm, the photobleaching is minimized, while the hyper-Raman scattering benefits from the electronic resonant enhancement. For S/R-2-butanol and L/D-tartaric acid, we were unable to detect the hyper-Raman optical activity at the sensitivity level of 1%. We also explored parasitic thermal effects which can be mitigating by varying the repetition rate of the laser source used for excitation of hyper-Raman scattering.

Taking into account the beam radii of pump light and seed laser along the entire length of the cell and their intensities in the cross section, a physical model with ordinary differential equation methods for alkali vapor amplifiers is established. Applied to the reported optically pumped Rb and diode-pumped Cs vapor amplifiers, the model shows good agreement between the calculated and measured dependence of amplified power on the seed power. A larger width of the spontaneous emission region as compared to the widths of pump absorption and laser emission regions, which will result in very high energy losses, is observed in the cell. Influence of pump and seed beam waists on output performance is calculated, showing that the pump and seed beam should match each other not only in shape but also in size, thus an optimal combination of beam radii is very important for efficient operation of alkali vapor amplifiers.

Combining the kinetic and fluid dynamic processes in static and flowing-gas diode-pumped alkali vapor lasers, a comprehensive physical model with three cyclically iterative algorithms for simulating the three-dimensional pump and laser intensities as well as temperature distribution in the vapor cell of side-pumped alkali vapor lasers is established. Comparison with measurement of a static side-pumped cesium vapor laser with a diffuse type hollow cylinder cavity, and with classical and modified models is made. Influences of flowed velocity and pump power on laser power are calculated and analyzed. The results have demonstrated that for high-power side-pumped alkali vapor lasers, it is necessary to take into account the three-dimensional distributions of pump energy, laser energy and temperature in the cell to simultaneously obtain the thermal features and output characteristics. Therefore, the model can deepen the understanding of the complete kinetic and fluid dynamic mechanisms of a side-pumped alkali vapor laser, and help with its further experimental design.

Combining the first-order ordinary differential equations of pump and laser power and the second-order ordinary differential equation of temperature, an optical model for diode-pumped alkali vapor lasers in two pumped configurations, is reported. This model, taking into account the axial distributions of pump and laser beam radii and the radial distributions of intensities and temperature, shows good agreement between the calculated and experimental results. An observed maximum temperature rise of ~58 K corresponding to a pump power of 20 W is reproduced, and a wide region of heat source density of quenching is predicted by the model. The heat production of relaxation and of quenching are demonstrated to be within an order of magnitude, indicating that quenching is as important as relaxation in the temperature calculation. It can also be deduced that the peak of the temperature profile is mainly dominated by relaxation, whereas its width can be attributed to thermal diffusion and quenching. In addition, dependencies of laser and thermal power on the pump beam waist are calculated, and an optimal ratio of 0.7 between the pump and laser beam waist is obtained.

On the basis of analysis of kinetic and thermodynamic processes of extremely high power CW exciplex pumped alkali vapor laser (XPAL), we establish a physical model to calculate and analyze 2-D and 3-D distributions of temperature as well as the intensity of laser beam in cavity with a different flowing velocity in the cell. Comparison between the simulated results of temperature distribution and laser characters of single-end and double-end scheme is drawn, demonstrating the advantages of double-end flow scheme, which actually means more homogeneous distributions of temperature and alkali atoms resulting in higher optical–optical efficiency. Enhancing pressure of argon to ~10 atm, with optimized pumped intensity of ${2.54\times 10}^{5}$ W/cm2 and optimized cavity length of 80 cm, we obtain more detailed simulated results of broadband pumped XPAL with four or five-level system.

Dimethyl sulfoxide (DMSO) is a biologically important solvent in part due to its dual miscibility with hydrophilic and hydrophobic molecules. Binary solutions of DMSO-water display non-ideal thermodynamics properties such as high viscosity and low freezing point due to hydrogen bonding. The unusual properties of DMSO-water solutions have been exploited to disrupt the formation of secondary structures of proteins during polymerase chain reaction assays and to act as a cryoprotectant for tissues. The exact coordination of the DMSO and water molecules remains unknown. Hyper- Raman scattering was employed for the first time to investigate binary systems of DMSO with water (H2O). As a part of this study, hyper-Raman and Raman spectra of pure solutions were first acquired and compared against existing Raman and IR spectroscopic data. Then the corresponding measurements were taken with deuterated DMSO-d6 and heavy water (D2O) to validate the analysis and to isolate overlapping spectral features. The permissive selection rules of hyper- Raman scattering provide new insight into disruptions of the self-hydrogen bonded networks of DMSO and water and the establishment of hydrogen bonded networks.

Raman spectroscopy is an essential optical tool for molecular fingerprints. The vibrational modes of biologically important molecules including proteins, nucleic acids and lipids have been studied to provide insight into their structure as well as insight into the metabolic processes and biomarker expression of cells. To explore hyper-Raman scattering as a complementary technique to Raman scattering, we build a laser system that can perform Raman and hyper-Raman scattering studies using a single setup. Using three amplification stages we are able to generate 8 ps, 1064 nm pulses at repetition rates up to 30 MHz. Converting the 1064 nm source laser to 532 nm, we achieve fast hyper-Raman detection and collect our spectrum with a commercial spectrometer and CCD. Using a single optical setup, we collect and compare Raman spectra at 532 nm to hyper-Raman spectra at 266 nm for water, ethanol and L-tartaric acid. Furthermore, we observe changes in the hyper-Raman peak intensities of an aqueous L-tartaric acid solution when selecting different laser repetition rates highlighting the need to control laser power and repetition rate to identify and mitigate thermal effects in biomolecules.

Analysis of two new pump-couplings: semi-ring and trapezoid LD side-pumped configurations in alkali vapor lasers is reported, which mainly includes the numerical approaches for evaluation of the pump intensity and temperature distribution in the cell of these two configurations. Comparison between the simulated results of the semi-ring and trapezoid LD side-pumped Cs vapor lasers and the experimental results of the single-side pumped Cs vapor lasers with a cylindrical white diffuse reflector and a stable or unstable resonator is made. Dependencies of laser power on pump power and flowed velocity for semi-ring, trapezoid, single and double side-pumped configurations are calculated, demonstrating the advantages of the semi-ring and trapezoid LD side-pumped configurations. Thus the model is very helpful for designing high-power side-pumped alkali vapor lasers.

Combining the kinetic and fluid dynamic processes in static and flowing-gas diode-pumped alkali vapor amplifiers, a comprehensive physical model with a cyclic iterative approach for calculating the three-dimensional temperature distribution of the vapor cell is established. Taking into account heat generation, thermal conductivity and convection, the excitation of the alkali atoms to high electronic levels, and their losses due to ionization in the gain medium, the thermal features and output characteristics have been simultaneously obtained. The results are in good agreement with those of the measurement in a static rubidium vapor amplifier. Influences of gas velocity on radial and axial temperature profiles are simulated and analyzed. The results have demonstrated that thermal problems in gaseous gain medium can be significantly reduced by flowing the gain medium with sufficiently high velocity.

A time dependent 3D model for pulsed diode-pumped Rb vapor laser is established by using the methods of circular cutting and alternating-direction implicit (ADI). The model is validated by comparing with Zhao’s experiment. The spatiotemporal distributions of intensities of pump light and laser, and population densities of different energy levels are presented and discussed in a single-pulse diode-pumped Rb vapor laser. The lasing dynamics and characteristics of a multi-pulse diode-pumped Rb vapor laser are also calculated and analyzed, and results show that higher peak power and average power of each laser pulse can be obtained if the pump power is greater. Moreover, for constant pump pulse width, the peak power of subsequent laser pulses (in addition to the first pulse) increases with increasing time interval between two adjacent pump pulses. For constant time interval between two adjacent pump pulses, the large pump pulse width is not conducive to improving the peak power of subsequent laser pulses.

A theoretical model is established to describe the thermal dynamics and laser kinetics in a static pulsed exciplex pumped Cs–Ar laser (XPAL). The temporal behaviors of both the laser output power and temperature rise in XPALs with a long-time pulse and multi-pulse operation modes are calculated and analyzed. In the case of long-time pulse pumping, the results show that the initial laser power increases with a rise in the initial operating temperature, but the laser power decreases quickly due to heat accumulation. In the case of multi-pulse operation, simulation results show that the optimal laser output power can be obtained by appropriately increasing the initial temperature and reducing the thermal relaxation time.

A physical model for a flowing four-side pumped alkali vapor laser MOPA system, which considers the saturation effect and amplified spontaneous emission (ASE) and cross-sectional temperature distribution, is established to simulate the output performance of the cesium vapor amplifier. According to the experimental parameters, the simulated result agrees well with the experiment, which demonstrates the validity of this model. Influences of the seed power, the flowing velocity, and the cell length on the amplified power are simulated and analyzed, and a set of optimal operating parameters are obtained. Thus, the model can provide an effective way for designing an efficient side-pumped flowing-gas alkali vapor amplifier.

A new method of pump-coupling in diode-pumped alkali vapor amplifier is reported, which uses ring-LD to tightly surround the alkali vapor cell for directly coupled side-pumping. The kinetic and fluid dynamic modeling, numerical approaches of the ring-LD side-pumped configuration are proposed and applied to the static and the flowing-gas Cs vapor amplifiers. Pump intensity and temperature distribution in the cell are simulated. Influences of some important factors on laser power are calculated and analyzed. Comparisons of different pumped configurations are made, demonstrating the highest utilizing efficiency of pump power of the ring-LD side-pumped configuration. Thus the model is very helpful for designing high-power side-pumped alkali vapor amplifiers.

Considering spectrally resolved absorption and temperature distribution, a physical model is established to describe the laser kinetic and thermodynamic processes of an exciplex pumped Rb vapor laser. A comparison with Carroll's model is made. Influences of pump intensity, temperature, reflectivity of output coupler, and number density of Kr on the performance of CW Rb-Kr XPAL with uniform temperature distribution are calculated and analyzed. Besides, with the heat accumulation considered, the temperature distribution was calculated, and the maximal optical-to-optical efficiency about 5.7% can be achieved at the condition of pump intensity I0 = 5.2 × 1010 W/m2 and flow velocity u = 250 m/s.

Calculations on the influence of compressible gas effects on the performances of exciplex pumped alkali vapor lasers (XPALs) with supersonic flow system are made. Modified configuration of experimental apparatus for XPALs is designed in this paper as well. On the basis of fluid mechanics and thermodynamics, theoretical derivations for the boundary of temperature gradient which actually is the position of shock wave plane are firstly deduced and presented. And our simulated results show that XPALs have broadband of not only in absorption spectrum but also in pump power, which will be helpful for researchers to find the way to make very high-power gas lasers. In addition, the simulating method to obtain the operating temperature of XPALs is given, and predicted the value, at the conditions of this paper, is 1500K with optimized parameters of Pp = 3×106 W, Tstag=513 K, initial Mach number = 2.5.

A physical model combining rate, power propagation, and transient heat conduction equations for diode-pumped alkali vapor lasers (DPAL) is applied to a pulsed Rb-CH4 DPAL, which agrees well with the time evolution of laser power and temperature measured by K absorption spectroscopy. The output feature and temperature rise of a multi-pulse DPAL are also calculated in the time domain, showing that if we energize the pump light when the temperature rise decays to 1/2, rather than 1/e of its maximum, we can increase the duty cycle and obtain more output energy. The repetition rate of >100Hz is high enough to achieve QCW (quasi-continuous-wave) laser pulses.