The streak tube imaging light detection and ranging (LiDAR) is a new type of waveform sampling laser imaging radar whose echo signals are stripe images with a high frame rate. In this study, the morphological and statistical characteristics of stripe signals are analyzed in detail. Based on the concept of mathematical morphology denoising, connected domains are constructed in a noisecontaining stripe image, and the noise is removed using the difference in connected domains area between signals and noises. It is shown that, for stripe signals, the proposed denoising method is significantly more efficient than Wiener filtering.

•Energy transfer between PM567:Rh610 dye-mixture in MPMMA matrices studied.•Fluorescence intensity of acceptor was improved 9 fold due to the energy transfer.•Highest slope efficiency was 70.4%, 8 times of that of acceptor doped sample.•Energy transfer rate constants and efficiencies were investigated.•Dominant mechanism responsible for the energy transfer is radiative type.In this paper, solid dye samples were prepared by codoping laser dyes Pyrromethene 567 (PM567) as the energy donor and Rhodamine 610 (Rh610) as the energy acceptor into the ethanol modified poly (methyl methacrylate) matrix (MPMMA) to enhance the properties of the solid dye lasers. The fluorescence intensity of the acceptor was enhanced by up to 9 fold with the introduction of the donor molecules. The laser efficiency of the dye mixture doped samples was improved by up to 8 times relative to that of the samples solely doped with the acceptor, and the highest slope efficiency was obtained as 70.4%. The radiative and nonradiative energy transfer rate constants (KR and KNR) were calculated using the Stern–Volmer plots and the acceptor concentration dependence of the radiative and nonradiative transfer efficiencies were also obtained. The KR was three orders of magnitude higher than the KNR, indicating the dominance of the radiative energy transfer mechanism in the present system. The deviation of the Stern–Volmer plot from the linearity demonstrated that both the dynamic and transient quenching mechanism exist in the present energy transfer system.

The effects of pressure and laser energy on the excitation temperature, electron number density and spark energy of laser induced plasmas (LIPs) in nitrogen were investigated using an ungated spectrometer with an electron multiplying charge-coupled device (EMCCD) camera as the detector. The plasmas were generated in nitrogen of 1.2×104 Pa to 1.0×105 Pa by 532 nm output of a 10 Hz Q-switched Nd:YAG laser with pulse energy ranging from 20 mJ to 100 mJ. The excitation temperatures were found around 3 eV, and varied little with pressure and laser energy. The electron number densities increased from 5.8×1017 cm−3 to 4.7×1018 cm−3 when the pressure was increased from 1.2×104 Pa to 1.0×105 Pa, but varied little with laser energy. The spark energy increased linearly with the input laser energy, and saturated at 35–60% of the input energy. Comparisons with results of time-resolved measurements and of other authors indicate that the ungated spectrometer can give reasonable results on excitation temperature and electron number density of LIPs, although it suffers intrinsic limitations involved with its inability to be time-resolved, and can serve as an option to lower systematic cost for practical applications of laser induced plasmas.Highlights► Laser induced plasmas in nitrogen are characterized using an ungated spectrometer. ► Electron temperatures are ∼3.0 eV, and vary little with laser energy and pressure. ► Electron densities increase with pressure, but vary little with laser energy. ► Time-resolved measurement confirmed the reliability of the ungated measurements.

Based on ultrafast laser pulses, time-resolved resonance enhancement coherent anti-Stokes Raman scattering (RE-CARS) is applied to investigate wave-packet dynamics in gaseous iodine. The effects of air pressure on the wave-packet dynamics of iodine molecules are studied at pressures ranging from 1.5 Torr to 750 Torr. The RE-CARS signals are recorded in a gas cell filled with a mixture of about 0.3 Torr iodine in air buffer gas at room temperature. The revivals and fractional revival structures in the wave-packet signal are found to gradually disappear with rising air pressure up to 750 Torr, and the decay behaviors of the excited B-state and ground X-state become faster with increasing air pressure, which is due to the collision effects of the molecules and the growing complexity of the spectra at high pressures.Highlights► This study presents the wavepacket dynamics of iodine under different air pressures. ► Collision effects of the molecules on the wavepacket dynamics is investigated by the dramatic RE-CARS. ► The time-resolved tool vividly shows collision effects on the revivals and fractional revivals of the wavepacket.

We utilize femtosecond time-resolved electronic resonance-enhanced coherent anti-Stokes Raman scattering (ERE-CARS) to investigate new information for pyrromethene 650 (PM650) dye molecules. For this purpose, the vibrational properties of PM650 are registered in diluted solutions of several organisms. We observe a strong Raman vibrational mode with a wavenumber difference of about 48 cm− 1 in its organic solutions. This may be linked to the intramolecular electron transfer (ICT) process from the aromatic ring to the cyano group in PM650. The influence of the solvent effects on the vibrational dynamics of PM650 is also investigated. The vibrational properties of PM650 dye molecules diluted in polar organic solutions are light solvent-dependent.

We utilize femtosecond time-resolved electronic resonance-enhanced coherent anti-Stokes Raman scattering (ERE-CARS) to study the vibrational dynamics of cresyl violet 670 (CV670) dye molecules. For this purpose, the vibrational properties of CV670 are registered in diluted solutions of ethanol and methanol. By changing the timing (Δt > 0) of the laser pulses of this nondegenerate four wave mixing technique, the wavepacket dynamics on the electronically ground state can be detected as oscillations in the ERE-CARS signal. Two strong Raman vibrational modes with an average period of 0.401 and 0.423 ps in CV670–ethanol solutions are obtained simultaneously, and we observe a qualitative vibrational dephasing time difference of the Raman vibrational modes of CV670 in ethanol and methanol solvents (5 × 10–5 mol/L), which may be due to the influence of the formation of the supramolecular structures in CV670–ethanol and CV670–methanol mixtures on the Raman modes of CV670.

The molecular dynamics process is investigated in this paper using a broadband fs time-resolved coherent anti-Stokes Raman spectroscopy (CARS) technique. By varying the timing of laser pulses, low vibrational states are started and studied on both the electronically excited B(3Π0u+) state and ground X(1Σ0g+) state of iodine in the gas phase at room temperature. According to change the pump wavelength or Stokes pulse as well as the wavelength of the detection window for the CARS signal, dynamics on different potential-energy surfaces can be accessed and detected by the CARS spectroscopy. Results show that the period of the oscillation is decreased for the excited B(3Π0u+) state as the wavelength of the pump pulses is increased, while it is increased for the ground X(1Σ0g+) state with the increase of the Stokes wavelength.

In this paper, ultrafast time-resolved coherent degenerate four-wave-mixing (DFWM) spectroscopy is performed to investigate molecular dynamics in the gaseous phase. Laser pulses lasting for 40 fs are used to create and monitor different vibrational eigenstates of iodine at room temperature (corresponding to a low saturation pressure of about 35 Pa). Using an internal time delay in the DFWM process resonant with the transition between the ground X-state and the excited B-state, the vibrational states of both the electronically excited and the ground states are detected as oscillations in the DFWM transient signal. The dynamics of either the electronically excited or ground state of iodine molecules obtained are consistent with the previous high temperature studies on the femtosecond time-resolved DWFM spectroscopy.Highlights► We investigated the iodine molecular dynamics in different states at room temperature. ► We used an internal time delay in the DFWM process resonant with the transition between the ground X-state and the excited B-state. ► Increasing DWFM signal will increase signal-to-noise ratio. ► Decreasing iodine vapor pressure will decrease various cross terms and interferences. ► Environmental and atmospheric measurements depend on the low-concentration monitor technique about real-time detection.

The two-photon absorption (TPA) characteristics of PMMA discs doped with three different dyes were studied using an fs-pulsed Ti-Sapphire laser as the pump source, and employing the open-aperture Z-scan technique. TPA cross-sections obtained for PMMA doped with the dyes PM597, DCM and rhodamine 6G–rhodamine B (co-doped) were found to be equal to 24.7, 33.3 and 32.3 GM, respectively (1 GM=10−50 cm4 s phot−1 mol−1). Furthermore, two-photon fluorescence was measured for the samples containing DCM and rhodamine 6G–rhodamine B (co-doped). Compared to the one-photon fluorescence spectrum, the peaks in the two-photon fluorescence spectrum were red shifted and the extent of red shift increased with increasing doping concentration. We have also observed that the red shift in the two-photon fluorescence peak of the samples in the solid form is much larger than that in the solution state. This phenomenon could be explained by a twisted intra-molecular charge transfer model.