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We present the spectroscopic and laser characteristics of a 3 at.% Tm:Y2O3 transparent ceramic at cryogenic temperatures. An absorption cross section of 4.7 × 10−21 cm2 with a bandwidth of 0.7 nm centered at 793.3 nm and an emission cross section of 29.0 × 10−21 cm2 centered at 1930.9 nm were estimated at 80 K. Continuous-wave laser operation was achieved using broadband and VBG stabilized laser diodes emitting around 793 nm as pump sources. With the VBG pump diode, a maximum output power of 6.4 W was achieved at 80 K corresponding to a slope efficiency of 52.0% with respect to absorbed power. [ABSTRACT FROM AUTHOR]

We performed first experiments to evaluate the potential of photoluminescence spectroscopy to detect microplastics using a 405 nm laser diode for sample excitation. A set of nine bulk plastic samples and nine samples of natural materials typically found in the marine environment were examined and compared. The plastic and non-plastic materials could be differentiated based on the shape of the acquired photoluminescence spectra. Our results show that photoluminescence spectroscopy holds the potential for reliable characterization of environmental samples regarding the microplastic content. [ABSTRACT FROM AUTHOR]

Hydroxyl radical (OH) is a key intermediate reactive species during combustion processes relevant to power production, transportation, and manufacturing. We demonstrate an OH sensor based on in situ laser absorption spectroscopy for deployment in industrial conditions. The sensor relies on telecommunications-fiber-coupled, tunable-diode-laser absorption spectroscopy of an OH transition near 1491 nm. By employing wavelength modulation spectroscopy, the sensor is capable of in situ, quantitative detection of OH down to mole fraction values of 10−5 over a 75-cm pathlength. To increase the accuracy of the OH sensor, we perform the first dual-comb spectroscopy measurement above a flame and use the results to create an absorption database of water vapor transitions from 1489.2 to 1492.5 nm at temperatures up to 2165 K. The database is included in the analysis procedure for the tunable diode laser sensor to account for the water vapor absorption that overlaps with the OH absorption. The utility of the laser sensor is demonstrated by characterizing the concentration of OH radical above a catalytic combustor under different operating conditions. [ABSTRACT FROM AUTHOR]

Lasing on different spectral lines belonging to a giant pulse of multi-line Q-switched CO laser was experimentally studied. The Q-switched CO laser emitted a giant microsecond pulse that consisted of about one hundred subpulses corresponding to different rotational-vibrational transitions. Amplitude, time delay and duration were measured for such a laser subpulse, and processes affecting formation of the CO laser giant pulse spectrum were analyzed. These data were taken into account to correctly estimate peak power and the number of spectral lines of radiation formed under sum frequency conversion of the CO laser radiation in nonlinear ZnGeP crystal. [ABSTRACT FROM AUTHOR]

The plasmonic analogy from Fano resonance to Autler-Townes splitting (ATS) in mid-infrared spectral range is observed assisted by a dual parallel graphene-coated grating structure. The analytical derivation exhibits a height-dependent resonance which is crucial for discerning Fano resonance from ATS. The mechanism of generating a transparency window seeks a trade-off between Fano resonance and ATS at threshold height. While within the critical height, Fano resonance dominates. The Akaike Information Criterion test is used to discern these two effects quantitatively. Moreover, the device pronounces a good tunability accompanied with a slowing light application. Our ideas open up a new insight view of designing or constructing highly integrated, multi-functional graphene-based metamaterials in nanoscale. [ABSTRACT FROM AUTHOR]

Ratios of the 2nd and 1st harmonics at the line center are very sensitive to absorbance, but not to line profiles when the modulation index is set to 0.94. Based on this characteristic, we proposed a method which uses the 1st and 2nd harmonics to measure the absolute absorbance, and then obtain gas pressure and concentration. Some transitions of CO and HO molecules near 6980 cm are selected to verify this method. The satisfactory agreement between measurement results and theoretical values validates the proposed method. [ABSTRACT FROM AUTHOR]

We report on a novel pseudothermal light source based on laser light coupled into an optical multimode fiber. The setup is simple, low cost, exhibits inherently high directional light emission and allows for a flexible arrangement. By measuring the photon statistics and spatial two point intensity correlations in the far field we show that the setup exhibits all characteristics of a Gaussian random source. [ABSTRACT FROM AUTHOR]

The cascade system has played an important role in contemporary research areas related to fields like Rydberg excitation, four wave mixing and non-classical light generation, etc. Depending on the specific objective, co or counter propagating pump-probe laser experimental geometry is followed. However, the stepwise excitation of atoms to states higher than the first excited state deals with increasingly much fewer number of atoms even compared to the population at first excited level. Hence, one needs a practical indicator to study the complex photon-atom interaction of the cascade system. Here, we experimentally analyze the case of rubidium 5S → 5P → 5D as a specimen of two-step excitation and highlight the efficacy of monitoring one branch, which emits ~420 nm, of associated cascade decay route 5D → 6P → 5S, as an effective monitor of the coherence in the system. [ABSTRACT FROM AUTHOR]

The origin of light emission during low-temperature combustion in a light-duty IC engine is investigated by high-speed spectroscopy in both HCCI and PPC regimes. Chemiluminescence and thermal radiation are expected to be the dominant sources of light emission during combustion. A method has been developed to distinguish chemiluminescence from thermal radiation, and different chemiluminescing species could be identified. Different combustion modes and global equivalence ratios are analyzed in this manner. The results indicate that the spectral signature (270-540 nm range) of the combustion is highly dependent on the stratification level. A significant broadband chemiluminescence signal is detected and superimposed on all spectra. This broadband chemiluminescence signal can reach up to 100 percent of the total signal in HCCI combustion, while it drops to around 80 percent for stratified combustion (PPC). We show that this broadband signal can be used as a measure for the heat release rate. The broadband chemiluminescence did also correlate with the equivalence ratio quite well in both HCCI and PPC regimes, suggesting that the total emission in the spectral region of 330-400 nm can serve as a proxy of equivalence ratio and the rate of heat release. Regarding C* chemiluminescence, we see two different chemical mechanisms for formation of C* in the PPC regime: first during the early stage of combustion by the breakup of bigger molecules and the second during the late stage of combustion when soot particles are forming. [ABSTRACT FROM AUTHOR]

We present a new cavity ring-down spectroscopy system which was developed for variable-temperature absorption measurements (220-290 K) of atmospheric gases. This laser spectrometer was developed in the framework of the NASA Orbiting Carbon Observatory-2 project to improve our understanding of line shape parameters for carbon dioxide and oxygen. The apparatus consists of a monolithic, fixed-mirror ring-down cavity within a temperature-regulated enclosure, which is interrogated by a tunable, single-frequency diode laser. We experimentally characterize and model the dependence of the spectrum detuning axis at each setpoint temperature, and show that absolute frequencies are stable to within 200 kHz over several hours, corresponding to temperature stabilities better than 1 mK. We measure the R16e (30013-0001) CO transition and carry out multi-spectrum analyses using two line profiles incorporating speed-dependent (quadratic approximation) and Dicke narrowing (hard collision assumption) effects. The resulting broadening coefficient and temperature exponent are in excellent agreement (0.05% level) with previous high-resolution Fourier-transform spectroscopy measurements, and the speed dependent broadening parameter is within 3% of the theoretical value. [ABSTRACT FROM AUTHOR]

Chiroptical methods facilitating enantioselective quantitative measurements with good temporal and spatial resolution are highly desirable for process monitoring, e.g., during the production of pharmaceuticals. The recently proposed enantioselective Raman (esR) spectroscopy has a great potential in this respect. The a priori knowledge of how the settings of the experimental parameters will affect the measurement is crucial to avoid systematic errors and to build an optimized setup. This work presents a ray tracing-based model for the simulation of light scattering experiments and uses it to investigate the effects of experimental parameters in esR spectroscopy. The main advancement to the previous work is that the model is implemented in 3D and takes a large variety of effects into account. The laser beam is considered as a Gaussian beam. The light scattered from the different volume elements illuminated by the laser is traced through the optical components of the signal collection system. The results indicate that the enantioselective characteristics of the method that were proposed for 1D are still valid in a 3D geometry. The contrast and sharpness in the polarization-resolved intensity distributions are moderately reduced compared to the idealized case. This is very promising for the practical application of the esR technique. The results confirm that it can be applied for a broad range of settings and substances. [ABSTRACT FROM AUTHOR]

Novel single-ended sensor arrangements are demonstrated for in situ absorption spectroscopy in combustion and related test articles. A single-ended optical access technique based on back-reflection from a polished test article surface is presented. HO vapor absorption spectra were measured at 10 kHz in a homogeneous-charge compression-ignition engine using a sensor of this design collecting back-reflection from a polished piston surface. The measured spectra show promise for high-repetition-rate measurements in practical combustion devices. A second sensor was demonstrated based on a modification to this optical access technique. The sensor incorporates a nickel retroreflective surface as back-reflector to reduce sensitivity to beam steering and misalignment. In a propane-fired furnace, HO vapor absorption spectra were obtained over the range 7315-7550 cm at atmospheric pressure and temperatures up to 775 K at 20 Hz using an external-cavity diode laser spectrometer. Gas properties of temperature and mole fraction were obtained from this furnace data using a band-shape spectral fitting technique. The temperature accuracy of the band-shape fitting was demonstrated to be ±1.3 K for furnace measurements at atmospheric pressure. These results should extend the range of applications in which absorption spectroscopy sensors are attractive candidates. [ABSTRACT FROM AUTHOR]

We report in situ measurements of non-uniform temperature, HO and CO concentration distributions in a premixed methane-air laminar flame using tunable diode laser absorption spectroscopy (TDLAS). A mid-infrared, continuous-wave, room-temperature interband cascade laser (ICL) at 4183 nm was used for the sensitive detection of CO at high temperature.The HO absorption lines were exploited by one distributed feedback (DFB) diode laser at 1343 nm and one ICL at 2482 nm to achieve multi-band absorption measurements with high species concentration sensitivity, high temperature sensitivity, and immunity to variations in ambient conditions. A novel profile-fitting function was proposed to characterize the non-uniform temperature and species concentrations along the line-of-sight in the flame by detecting six absorption lines of CO and HO simultaneously. The flame temperature distribution was measured at different heights above the burner (5-20 mm), and compared with the thermocouple measurement with heat-transfer correction. Our TDLAS measured temperature of the central flame was in excellent agreement (<1.5% difference) with the thermocouple data.The TDLAS results were also compared with the CFD simulations using a detailed chemical kinetics mechanism (GRI 3.0) and considering the heat loss to the surroundings.The current CFD simulation overpredicted the flame temperature in the gradient region, but was in excellent agreement with the measured temperature and species concentration in the core of the flame. [ABSTRACT FROM AUTHOR]

We present an echelle spectrograph that is optimized for characterization of frequency combs for astronomical applications (astro-combs). In spite of its very compact and cost-efficient design, it allows viewing the spectrum of a frequency comb in nearly the same way as a full-sized high-resolution echelle spectrograph as used at astronomical observatories. This is of great value for testing and characterizing astro-combs during their assembly phase. The spectrograph can further be utilized to effectfully demonstrate the remarkable capabilities of astro-combs. [ABSTRACT FROM AUTHOR]

Transient energy transfer effect might occur in femtosecond pump-probe optical Kerr gate (OKG) measurements. Using time- and frequency-resolved two-dimensional pump-probe imaging spectroscopy, we are able to obtain the OKG spectra as a function of the delay time between pump and probe pulses. By analyzing the pump power dependence of the OKG spectra at different delay time, we find that due to the effect of transient energy transfer, the short-wavelength components of the OKG spectra are enhanced when the delay of the probe to pump pulse is positive, while the long-wavelength components increase when the delay is negative. [ABSTRACT FROM AUTHOR]

This paper reports on the development of the tunable diode laser absorption spectroscopy sensor near 4350 cm (2298 nm) for measurements of CO and HO mole fractions and soot volume fraction under gasification conditions. Due to careful selection of the molecular transitions [CO ( υ″ = 0 → υ′ = 2) R34-R36 and HO at 4349.337 cm], a very weak (negligible) sensitivity of the measured species mole fractions to the temperature distribution inside the high-temperature zone (1000 K < T < 1900 K) of the gasification process is achieved. The selected transitions are covered by the tuning range of single diode laser. The CO and HO concentrations measured in flat flames generally agree better than 10 % with the results of 1-D flame simulations. Calibration-free absorption measurements of studied species in the reactor core of atmospheric pilot-scale entrained-flow gasifier operated at 0.1 MW power are reported. Soot concentration is determined from the measured broadband transmittance. The estimated uncertainties in the reactor core CO and HO measurements are 15 and 20 %, respectively. The reactor core average path CO mole fractions are in quantitative agreement with the µGC CO concentrations sampled at the gasifier output. [ABSTRACT FROM AUTHOR]

The hyperfine structure of the 5 d6 sD → 5 d6 s6 pF transition of the radioactive isotope Lu has been investigated by laser photoionization spectroscopy. Measured spectra permitted the determination of hyperfine magnetic dipole constants and electric quadrupole constants for ground and excited state as well as the isotope shift of the Lu isotope. The data obtained were used to confirm the selective photoionization of Lu from a neutron-irradiated sample that initially had a natural isotope composition. A concentration for Lu of 50 % was achieved, and the photoionization efficiency was estimated as suitable for technological application. [ABSTRACT FROM AUTHOR]

To decrease the risk of bilirubin encephalopathy and minimize the need for exchange transfusions, we report a novel design for light source of light-emitting diode (LED)-based neonatal jaundice therapeutic device (NJTD). The bilirubin absorption spectrum in vivo was regarded as target. Based on spectral constructing theory, we used commercially available LEDs with different peak wavelengths and full width at half maximum as matching light sources. Simple genetic algorithm was first proposed as the spectral matching method. The required LEDs number at each peak wavelength was calculated, and then, the commercial light source sample model of the device was fabricated to confirm the spectral matching technology. In addition, the corresponding spectrum was measured and the effect was analyzed finally. The results showed that fitted spectrum was very similar to the target spectrum with 98.86 % matching degree, and the actual device model has a spectrum close to the target with 96.02 % matching degree. With higher fitting degree and efficiency, this matching algorithm is very suitable for light source matching technology of LED-based spectral distribution, and bilirubin absorption spectrum in vivo will be auspicious candidate for the target spectrum of new LED-based NJTD light source. [ABSTRACT FROM AUTHOR]

The high-harmonic generation in a two-color laser field, consisting of a 30-fs Ti:Sapphire laser pulse and its second harmonic, could be enhanced by installing an extra gas medium of Ar in front of the harmonic generation medium of He. The effects of the extra medium were examined by analyzing harmonic spectra taken under different experimental conditions. The observed characteristics of enhanced harmonic generation were explained in terms of the profile modification of the two-color laser beam. The 34th harmonic at 23.5 nm and 38th harmonic at 21.5 nm were enhanced 2.5 and 2 times, respectively. [ABSTRACT FROM AUTHOR]

We report the development of a three-beam spectral-domain Doppler optical coherence tomography setup that allows single interferometer-based measurement of absolute flow velocity. The setup makes use of galvo-based phase shifting to remove complex conjugate mirror artifact and a beam displacer in the sample arm to avoid cross talk image. The results show that the developed approach allows efficient utilization of the imaging range of the spectral-domain optical coherence tomography setup for three-beam-based velocity measurement. [ABSTRACT FROM AUTHOR]

The influence of the surrounding gas conditions on the surface integrity in the micro-drilling of silicon carbide was experimentally investigated using ns pulsed laser of 266 nm wavelength. Moreover, micro-machining characteristics were observed using high-speed shutter and video cameras in the micro-drilling of silicon carbide. The size and intensity of the laser-induced plasma were larger, and the plasma affected area was larger and deeper in argon than that in air. Although the intensity of the plasma was lower in helium than that in other gases, the surface around the drilled hole was roughened by the spread of the plasma in the vicinity of the drilled hole. Debris was removed along the flow field generated by laser shot in the opposite direction to the laser irradiation. The gas flow behavior and the spectrum and intensity of the laser-induced plasma were influenced by the surrounding gas type and pressure. The appearance of plasma generation affected the surface integrity at the circumference of the drilled hole, and the surface integrity was improved by reducing the pressure. [ABSTRACT FROM AUTHOR]

Optical feedback frequency-stabilized cavity ring-down spectroscopy (OFFS-CRDS) is a near-shot-noise-limited technique combining a sensitivity of $$2\times 10^{-13}\,{\mathrm {cm^{-1}/\sqrt{Hz}}}$$ with a highly linear frequency axis and sub-kHz resolution. Here, we give an in-depth review of the key elements of the experimental setup encompassing a highly stable V-shaped reference cavity, an integrated Mach-Zehnder modulator and a tightly locked ring-down cavity with a finesse of 450,000. Carrying out a detailed analysis of the spectrometer performance and its limitations, we revisit the photo-electron shot-noise limit in CRDS and discuss the impact of optical fringes. We demonstrate different active schemes for fringe cancelation by varying the phase of parasitic reflections. The proof-of-principle experiments reported here include a broadband high-resolution spectrum of carbon dioxide at 1.6 µm and an isolated line-shape measurement with a signal-to-noise ratio of 80,000. Beyond laboratory-based absorption line metrology for fundamental research, OFFS-CRDS holds a considerable potential for field laser measurements of trace gas concentrations and isotopic ratios by virtue of its small sample volume and footprint, the robust cavity-locking scheme and supreme precision. [ABSTRACT FROM AUTHOR]

We demonstrate mid-infrared dual-comb spectroscopy with an optical parametric oscillator (OPO) toward real-time field measurement. A singly resonant OPO based on a MgO-doped periodically poled lithium niobate (PPLN) crystal is demonstrated. Chirped mirrors are used to compensate the dispersion caused by the optical cavity and the crystal. A low threshold of 17 mW has been achieved. The OPO source generates a tunable idler frequency comb between 2.7 and 4.7 μm. Dual-comb spectroscopy is achieved by coupling two identical Yb-fiber mode-locked lasers to this OPO with slightly different repetition frequencies. A measured absorption spectrum of methane is presented with a spectral bandwidth of $$300\,\hbox {cm}^{-1}$$ , giving an instrumental resolution of $$0.4\,\hbox {cm}^{-1}$$ . In addition, a second OPO containing two MgO-doped PPLN crystals in a singly resonant ring cavity is demonstrated. As such, this OPO generates two idler combs (average power up to 220 mW), covering a wavelength range between 2.7 and 4.2 μm, from which a mid-infrared dual-comb Fourier transform spectrometer is constructed. By detecting the heterodyned signal between the two idler combs, broadband spectra of molecular gases can be observed over a spectral bandwidth of more than $$350\,\hbox {cm}^{-1}$$ . This special cavity design allows the spectral resolution to be improved to $$0.2\,\hbox {cm}^{-1}$$ without locking the OPO cavity, indicating that this OPO represents an ideal high-power broadband mid-infrared source for real-time gas sensing. [ABSTRACT FROM AUTHOR]

The design and characterization of a near-IR Chirped Laser Dispersion Spectroscopy (CLaDS) sensor for atmospheric methane detection are reported. The near-IR CLaDS system exhibits the benefits of the prior mid-IR CLaDS systems implemented for open-path sensing while taking advantage of the robust fiber-optic components available in the near-IR. System noise, long-term stability, and comparison with existing technology for methane detection are presented. [ABSTRACT FROM AUTHOR]

An analytical propagation formula for a focused polychromatic partially coherent flat-topped beam with circular symmetry is derived in a tensor form that is based on the alternative flat-top beams model proposed by Li (Opt Lett 27:1007, ). The dependence of the relative spectral shift on the flat-top order N is investigated numerically in detail. It is shown that the on-axis maximum relative spectral shift occurs at the back focal plane, while the no spectral shift observes at the image plane. Furthermore, we report the experimental generation of a polychromatic partially coherent FT beam. The on-axis and off-axis spectral measurement verifies the theoretical study. [ABSTRACT FROM AUTHOR]

We report on the storage of orbital angular momentum (OAM) of light of a Laguerre-Gaussian mode in an ensemble of cold cesium atoms and its retrieval along an axis different from the incident light beam. We employed a time-delayed four-wave mixing (FWM) configuration to demonstrate that at small angle (2°), after storage, the retrieved beam carries the same OAM as the one encoded in the input beam. A calculation based on mode decomposition of the retrieved beam over the Laguerre-Gaussian basis is in agreement with the experimental observations done at small angle values. However, the calculation shows that the OAM retrieving would get lost at larger angles, reducing the fidelity of such storing-retrieving process. In addition, we have also observed that by applying an external magnetic field to the atomic ensemble the retrieved OAM presents Larmor oscillations, demonstrating the possibility of its manipulation and off-axis retrieval. [ABSTRACT FROM AUTHOR]

In this paper , we present a technique for the precise measurement of electric dipole-allowed transitions in trapped ions. By applying a probe and a cooling laser in quick succession, the full transition can be probed without causing distortion from heating the ion. In addition, two probes can be utilized to measure a dispersion-like signal, which is well suited to stabilizing the laser to the transition. We have fully characterized the parameters for the measurement and find that it is possible to measure the line center to better than 100 kHz with an interrogation time of 30 s. The long-term stability of the spectroscopy signal is determined by employing two independent ion trap systems. The first ion trap is used to stabilize the spectroscopy laser. The second ion trap is then employed to measure the stability by continuously probing the transition at two frequencies. From the Allan variance, we obtained a frequency instability of $$1\cdot 10^{-10}$$ for an interrogation time of 1,000 s. [ABSTRACT FROM AUTHOR]

We propose an approach for absolute velocity measurement where the use of a beam displacer provides two orthogonal linearly polarized beams to probe the sample simultaneously at two different incidence angles. The approach helps remove the cross talk image and facilitates single detector-based Fourier domain Doppler velocity measurement. The system has been characterized by quantifying absolute flow velocity in a flow phantom. [ABSTRACT FROM AUTHOR]

We present measurements of the absorption and emission cross-sections for Yb:YAG, Yb:LuAG and Yb:CaF as a function of temperature between 80 and 340 K. The cross-sections are determined by the combination of the McCumber relation and the Fuchtbauer-Ladenburg (FL) equation to achieve reliable results in spectral regions of high and low absorption. The experimental setup used for the fluorescence measurements minimizes re-absorption effects due to the measurement from small sample volume, providing nearly undisturbed raw data for the FL approach. The retrieved cross-sections together with the spectral characteristics of the tested materials provide important information for the design of energy efficient, high-power laser amplifiers. [ABSTRACT FROM AUTHOR]

We report on diode-pumped laser operation of Pr,Mg:SrAlO at lasing wavelengths of λ = 724.4 nm, λ = 643.5 nm, and λ = 622.8 nm. Furthermore, the laser threshold could be reached in the green spectral range. By pumping the crystal longitudinally from each side with two polarization beam combined InGaN laser diodes, a total pump power of ≈4 W was available. In the deep red spectral range, a maximum output power of 564 mW was achieved with a maximum slope efficiency of 50 % with respect to the absorbed pump power. The maximum possible internal losses were estimated to ≈1 %. Beam quality factors M were in the range of 1.2-1.5. [ABSTRACT FROM AUTHOR]

An asymmetric chiral metamaterial (CMM) circular polarizer based on bilayer twisted split-ring resonator structure was proposed and investigated. Both numerical simulations and experiments reveal that when a y-polarized wave is incident on this CMM propagating along backward (− z) direction, the two linear components of the transmitted wave have nearly equal amplitudes and 90°(−90°) phase difference at the resonant frequencies. This means that the right-hand circular polarization and left-hand circular polarization are realized in transmission at 6.4 and 8.1 GHz, respectively. The surface current distributions are studied to illustrate the transformation behavior for both circular polarizations. Further, the influences of the structural parameters of the circular polarizer to the transformation transmissions spectra have been investigated numerically. [ABSTRACT FROM AUTHOR]

The polarized absorption, emission spectra and decay time measurements of Pr-doped CaYAlO single crystal have been performed at room temperature. Based on the Judd-Ofelt theory, the spectroscopic parameters $$\Upomega_{t} (t = 2,4,6)$$ , radiative transition probabilities, radiative lifetimes and branching ratios were obtained. The stimulated emission cross-section, fluorescence lifetimes and the quantum efficiency of the promising laser transition were also calculated and compared with other reported crystals. The results show that Pr:CaYAlO is a promising candidate for visible solid-state laser emission. [ABSTRACT FROM AUTHOR]

A Nd:NaLa(WO) crystal with dimensions of ϕ 17 × 30 mm was grown by the Czochralski method. The thermal expansion coefficients of Nd:NaLa(WO) crystal are 1.32 × 10 K along c-axis and 1.23 × 10 K along a-axis, respectively. The spectroscopic characteristics of Nd:NaLa(WO) crystal were investigated. The Judd-Ofelt theory was applied to calculate the spectral parameters. The absorption cross sections at 805 nm are 2.17 × 10cm with a full width at half maximum (FWHM) of 15 nm for π-polarization, and 2.29 × 10cm with a FWHM of 14 nm for σ-polarization. The emission cross sections are 3.19 × 10cm for σ-polarization and 2.67 × 10cm for π-polarization at 1,064 nm. The fluorescence quantum efficiency is 67 %. The quasi-cw laser of Nd:NaLa(WO) crystal was performed. The maximum output power is 80 mW. The slope efficiency is 7.12 %. The results suggest Nd:NaLa(WO) crystal as a promising laser crystal fit for laser diode pumping. [ABSTRACT FROM AUTHOR]

In this paper, tunable diode laser absorption spectroscopy humidity measurements with an ultra-compact measurement cell are presented. The optical path length is 2 cm. The system uses a vertical cavity surface emitting laser at 1.854 μm. The main limiting factor of the humidity resolution is not the noise but interference fringes produced by reflecting surfaces. Next to the system setup, a novel rejection method to eliminate these fringes, based on Fourier domain analysis of the absorption line, is described. In contrast to other fringe rejection methods, the presented method is able to handle fringes, whose free spectral range is in the range of the half width of the absorption line. The achievable humidity resolution for the presented cell is below 0.25 % relative humidity at room temperature. [ABSTRACT FROM AUTHOR]

Direct seeding with a high-harmonic generation (HHG) source can improve the spectral, temporal, and coherence properties of a free-electron laser (FEL) and shall reduce intensity and arrival-time fluctuations. In the seeding experiment sFLASH at the extreme ultraviolet FEL in Hamburg FLASH, which operates in the self-amplified spontaneous emission mode (SASE), the 21st harmonic of an 800 nm laser is refocused into a dedicated seeding undulator. For seeding, the external light field has to overcome the noise level of SASE; therefore, an efficient coupling between seed pulse and electron bunch is mandatory. Thus, an HHG beam with a proper divergence, width, beam quality, Rayleigh length, pointing stability, single-shot pulse energy, and stability in the 21st harmonic is needed. Here, we present the setup of the HHG source that seeds sFLASH at 38.1 nm, the optimization procedures, and the necessary diagnostics. [ABSTRACT FROM AUTHOR]

Two similar 4 K 22-pole trapping machines have been recently completed in our laboratory. As a first experimental test in one of them, CH and HO ions have been trapped in the presence of helium gas at 3.8 K and the kinetics and temperature dependence of He tagging investigated. A first shell closure with 5 and (3 + 2) attached He atoms, respectively, is observed for both species. Applying IR radiation in the 3 μm region, helium attachment to CH is hindered by exciting CH-stretches of CH prior to attachment. The resulting spectroscopic signal shows that the kinetic temperature of the stored CH ensemble is below 12 K. [ABSTRACT FROM AUTHOR]

Versatile methods for the manipulation of individual quantum systems, such as confined particles, have become central elements in current developments in precision spectroscopy, frequency standards, quantum information processing, quantum simulation, and alike. For atomic and some subatomic particles, both neutral and charged, a precise control of magnetic fields is essential. In this paper, we discuss possibilities for the creation of specific magnetic field configurations which find application in these areas. In particular, we pursue the idea of a magnetic bottle which can be switched on and off by transition between the normal and the superconducting phase of a suitable material in cryogenic environments, for example, in trap experiments in moderate magnetic fields. Methods for a fine-tuning of the magnetic field and its linear and quadratic components in a trap are presented together with possible applications. [ABSTRACT FROM AUTHOR]

The previous investigations on nanosecond laser pulse interactions with breakdown plasma in a gas medium confined in a microhole have been limited. This kind of plasma has been studied in this paper. Due to the significant measurement difficulty resulted from the very small spatial and temporal scales involved, a physics-based computational model has been employed as the investigation tool. The model is developed by solving gas dynamic equations numerically using the finite difference method based on an essentially non-oscillatory scheme. The gas dynamic equations are coupled with suitable equation of state, where the electron number density for plasma region is calculated through the Saha equation. Using the model, the spatial confinement effects of the microhole sidewall on the plasma evolution under laser radiation have been investigated. It has been found that under the studied conditions the hole sidewall confinement can greatly enhance the plasma temperature, pressure, and thrust (over the same surface area). The enhancement should be due to the sidewall’s restriction on the plasma lateral expansion and the sidewall’s reflection of the pressure wave induced by plasma. This study implies potential advantages of the breakdown plasma confined in a microhole in many relevant applications, such as laser propulsion and laser-induced breakdown spectroscopy. The developed model also provides a useful guiding tool for future fundamental research and practical applications in many areas related to laser interactions with gas breakdown plasma. [ABSTRACT FROM AUTHOR]

A new application of the Paul wavelet algorithm was presented to determine the refractive index dispersion of a dielectric film from transmittance spectrum in the visible and near infrared region. The developed algorithm was tested by simulated data and experimentally applied to a sample of mica. The obtained refractive index dispersion determined by the Paul wavelet algorithm was compared with the refractive index values determined by the envelope and fringe counting methods, and also with the established result. It was shown that the degree of the Paul wavelet has a major effect on the outcome of a refractive index determination. The noise immunity of the presented method was shown by the simulation study. [ABSTRACT FROM AUTHOR]

A new method named photothermal diffuse reflectance (PTDR) is presented. This method combines the diffuse reflectance spectroscopy with the photothermal technique and is particularly suited for the investigation of strongly scattering samples. This method takes advantage of the high spectral selectivity and absorption of the mid-infrared region with the larger scattering cross section and high detector sensitivity available in the near-infrared. A model describing the PTDR method is proposed and supported with experimental results. The potential of the PTDR technique is illustrated by experimental signals obtained from various scattering media like polymers, liquids and powders. [ABSTRACT FROM AUTHOR]

We show that the coherent manipulation of molecular wavepackets in the excited states of trp-containing dipeptides allows efficient discrimination among them. Optimal dynamic discrimination fails, however, for some dipeptide couples. When considering the limited spectral resources at play (3 nm bandwidth at 266 nm), we discuss the concept of discriminability, which appears uncorrelated to both static spectra and relaxation lifetimes. [ABSTRACT FROM AUTHOR]

We present a simple and efficient technique for the generation of ultrashort deep-ultraviolet pulses based on four-wave mixing of noncollinear laser pulses in a thin solid. Sub-30-fs pulses (Fourier-limit of 13 fs) centered at 270 nm, with energies up to 6 μJ, were obtained by mixing the fundamental and the second harmonic of a Ti:sapphire amplifier in fused silica. Temporal characterization was performed with a dispersionless self-diffraction FROG setup. Spectra as broad as 20 nm were also obtained that can in principle support sub-4-fs deep-ultraviolet pulses.The results are well described by two-dimensional numerical simulations. [ABSTRACT FROM AUTHOR]

Two multi-harmonic detection methods for wavelength modulation spectroscopy (WMS) systems are presented and compared. The two possibilities discussed in this paper are: simultaneous curve fitting of multiple harmonic spectra, and reconstruction of the transmission from harmonic coefficients. The optimum number of harmonics is four and 25 harmonics, respectively. Compared with standard single-harmonic curve fitting, the methods give about a factor of 3 better performance than standard second-harmonic curve fitting. Concluding, multi-harmonic detection is better than single-harmonic detection and should be used if the system bandwidth is high enough to allow for proper detection of the higher harmonics. [ABSTRACT FROM AUTHOR]

Detailed structural and spectroscopic characterizations of Pr:YO nanophosphor have been carried out. On ultraviolet light (at 266 nm) excitation, intense red emission along with weak emissions in blue, green and infrared regions have been observed. The phenomena for the observed emission have been thoroughly explained in the present work and it was finally concluded that the direct excitation through low-lying 4f5d band of Pr ions and through the conduction band of YO nanophosphor are the main channels for the observed emissions. The calculated quantum efficiency (QE) for the red emission is found to be ~80 % while the CIE coordinates are (0.65, 0.34) quite close to the standard values. These studies clearly indicate that Pr:YO nanophosphors are promising and futuristic red luminescent material for the development of various display devices and UV detectors. Time resolved spectroscopy has been further used to investigate luminescence dynamics. [ABSTRACT FROM AUTHOR]

Scintillation evaluations for Laguerre-Gaussian (LG) beams for slant paths are made using Rytov approximation. On- and off-axis scintillation is formulated and calculated up to several tens of kilometers of slant distances for different zenith angles. Scintillation index variations against radial receiver point and different source sizes are also investigated. In all cases evaluated, it is found that LG beams with higher radial mode numbers result in less scintillation than Gaussian beam. Kolmogorov spectrum function is utilized in the scintillation calculations. [ABSTRACT FROM AUTHOR]

We demonstrate experimentally that the resolution of amplitude noise spectrum in Cs atomic vapor can be enhanced by narrowing the absorption using velocity selective optical pumping technique. It is found that the steep atomic dispersion accompanied by high absorption leads to more conversion of laser phase noise to amplitude noise, when the field propagates throughout the atoms, and meanwhile the spectral resolution is improved. The effect of optical pumping intensity on the spectrum resolution is experimentally discussed, and a theoretical explanation for this phenomenon is given, which shows that the phase-to-amplitude noise conversion is directly proportional to the dispersion of medium. [ABSTRACT FROM AUTHOR]

The broadband spectral conversion from near-UV absorption into near-infrared emission around 1 μm is reported in the ZnO-LiYbO hybrid phosphor, which is the benefit from the efficient energy transfer from ZnO to the Yb ions that are specifically located at the interfacial diffusion regions between ZnO and LiYbO, rather than those in LiYbO crystals. The Li-related and Yb-related defect energy levels are formed inside the ZnO band gap in the ZnO-LiYbO hybrid phosphor; the former act as the quenching centers for the excitons in ZnO and meanwhile the efficient energy donors for Yb ions, and the latter are responsible for the red shift of ZnO visible emission when the excitation energy is lower than E. The excitation power dependence of Yb emission intensities is measured to investigate the number of photons that are involved in the energy transfer process, which reveals that there are two channels for the sensitizing of Yb: One is due to the energy transfer by the recombination of electrons and holes, which is a cooperative energy transfer process, and the other is via the energy feeding from the Li-related energy levels, which is a phonon-assistant energy transfer process. [ABSTRACT FROM AUTHOR]

In this work, we report the optical waveguide formation in LiTaO crystal via Ar ion irradiation at an energy of 180 MeV and a fluence of 2×10 cm. The surface damage behavior of LiTaO crystal and structure change along the ion trajectory are studied through Rutherford backscattering/channeling spectra and micro-Raman spectra, respectively. The modal profile measurement through end-face coupling proves that the LiTaO waveguide can effectively support multimode propagation in the visible (633 nm) and single-mode propagation in the near-infrared (1539 nm) telecommunication wavebands. The waveguide propagation loss at 633 nm is measured by the back-reflection method. [ABSTRACT FROM AUTHOR]

We present direct optical extinction measurements on free size filtered iron oxide nanoparticles in the size range between 3 nm and 10 nm diameter. The high number density of nanoparticles required for the cavity enhanced absorption spectroscopy (CEAS) measurements was achieved by combining a high intensity plasma synthesis source of iron oxide particles with an aerodynamic lens inlet into the vacuum system and radiofrequency particle guiding and storage devices. The extinction cross sections can be quantitatively explained using the bulk optical constants of hematite, which may exist in the form of nanoparticles in the mesosphere. [ABSTRACT FROM AUTHOR]

We investigated the generation of cascaded four-wave mixing (CFWM) sidebands by using two crossing chirped femtosecond pulses with the same central wavelength in tellurite glass (Te glass). Sidebands of broadband spectra, which contained non-degenerate and degenerate CFWM signals, were obtained at different delay time between two input pulses. The CFWM sidebands observed on different sides of input beams were flexibly controlled by adjusting the delay time. [ABSTRACT FROM AUTHOR]