Μm Laser Excitation Research Articles

Tunable optical nonlinearities and surface plasmon resonance in Fe3O4 nanoparticles-decorated Ti3C2 MXene composite for ultrafast fiber lasers

In this work, the Ti3C2 MXene was modified with Fe3O4 nanoparticles to obtain a composite with in-plane optical anisotropy and surface plasmon properties. Based on a side-polished D-shaped fiber (DSF), this Fe3O4/Ti3C2 MXene (F/M) composite exhibits a tunable nonlinear optical (NLO) absorption response under 1.5 μm laser excitation with different polarization states. The modulation depths can be obtained from 0.9% to 12.1%. As an application, the ultrafast erbium-doped fiber laser (EDFL) with multiple pulsed laser operations was demonstrated using the F/M-DSF device as a saturable absorber (SA). Both stable Q-switching and mode-locking operations were demonstrated in the same all-fiber laser cavity, which generated pulsed laser with microsecond and sub-picosecond durations respectively. In addition, the bound state (BS) of solitons in harmonic mode-locked lasers with the pulse time interval of 3 ps and the highest order of 30th was also realized. This versatile and simple-structured all-fiber laser has great potential in various applications, such as optical communication. With the numerical simulations, the dynamic of F/M composite-based soliton mode-locking was also explored, illustrating the mechanism of soliton formation and propagation. This work not only expands the advanced applications of F/M composite in ultrafast photonics but also provides a new perspective for designing and optimizing its ultrafast modulating performance.

Comparative studies of long-wave laser-induced breakdown spectroscopy emissions excited at 1.064 µm and eye-safe 1.574 µm.

In this work, comparative long-wave infrared (LWIR) laser-induced breakdown spectroscopy (LIBS) emission studies of two excitation sources: conventional 1.064 μm and eye-safe laser wavelength at 1.574 μm were performed to analyze several widely-used inorganic energetic materials such as ammonium and potassium compounds as well as the organic liquid chemical warfare agent simulant, dimethyl methylphosphate (DMMP). LWIR LIBS emissions generated by both excitation sources were examined using three different detection systems: a single element liquid nitrogen cooled Mercury Cadmium Telluride (MCT) detector, an MCT linear array detection system with multi-channel preamplifiers + integrators, and an MCT linear array detection system with readout integrated circuit. It was observed that LWIR LIBS studies using an eye-safe pump laser generally reproduced atomic and molecular IR LIBS spectra as previously observed under 1.064 µm laser excitation.

Germanium-on-SOI waveguides for mid-infrared wavelengths.

We report on the development of Germanium-on-SOI waveguides for mid-infrared wavelengths. The strip waveguides have been formed in 0.85 and 2 μm thick Ge grown on SOI substrate with 220 nm thick Si overlayer. The propagation loss for various waveguide widths has been measured using the Fabry-Perot method with temperature tuning. The minimum loss of ~8 dB/cm has been achieved for 0.85 μm thick Ge core using 3.682 μm laser excitation. The transparency of these waveguides has been measured up to at least 3.82 μm.

Erbium-doped yttria thin films prepared by metal organic decomposition for up-conversion

Er:Y2O3 thin films have been obtained by spin coating process. Precursor solutions were prepared using nitrates as metal precursors and water as solvent. Citric, malic, and lactic acids were used as complexant. Investigations on resin compositions and on their coating parameters have been made, leading to crack-free thin films with citric and malic acids after direct deposition under standard room conditions (temperature, pressure and atmosphere). The films are homogeneous with a low root mean square roughness, less than 2.5nm. We demonstrated that the nature of the carboxylic acid is the key point to obtain high quality thin films on silicon substrates from 20nm up to 230nm thick, while the film porosity is related to the number of carbon in the acid molecule. All films exhibit up-conversion luminescence in the near infrared and in the visible range, under 1.54μm laser excitation. Furthermore, the up-conversion luminescence intensity increases with the applied annealing temperature on the films, due to an improvement of their crystallinity and to the total decomposition of organics.

Resonant excitation of precursor molecules in improving the particle crystallinity, growthrate and optical limiting performance of carbon nano-onions

A catalyst-free and highly efficient synthetic method for growing carbon nano-onions(CNOs) in open air has been developed through the laser resonant excitationof a precursor molecule, ethylene, in a combustion process. Highly concentricCNO particles with improved crystallinity were obtained at a laser wavelength of10.532 µm through the resonantexcitation of the CH2 wagging mode of the ethylene molecules. A higher growth rate up to2.1 g h − 1 was obtained, compared with that without a laser(1.3 g h − 1). Formation of the CNOs with ordered graphitic shells is ascribed tothe decomposition of polycyclic aromatic hydrocarbons (PAHs) intoC2 species. The optical limiting performances of the CNOs grownby the combustion processes were investigated. CNOs grown at10.532 µm laser excitation demonstrated improved optical limiting properties due to the improvedcrystallinity.

Effect of growth temperature on defect states of GaAsSbN intrinsic layer in GaAs∕GaAsSbN∕GaAs photodiode for 1.3μm application

A GaAsSbN layer closely lattice matched to GaAs was used as an intrinsic layer (i layer) in a GaAs∕GaAsSbN∕GaAs p-i-n photodiode with response up to 1.3μm. Deep level transient spectroscopy measurement on the GaAs∕GaAsSbN∕GaAs reveals two types of hole traps (HTs) in the GaAsSbN i layer; (i) HT1: a shallow N-related defect state (Ea∼0.10–0.12eV) and (ii) HT2: an AsGa point defect-related midgap defect state with Ea∼0.42–0.43eV. Reduction in growth temperature from 480to420°C reduces the HT2 trap concentration from 4×1015to1×1015cm−3, while increases the HT1 trap concentration from 1×1014to7×1014cm−3. Reduction in the HT2 trap concentration following growth temperature reduction was attributed to the suppression of AsGa point defect formation. Evidence of possible change of the AsGa midgap state to a shallow level defect due to the formation of (AsGa–NAs) pairs was also suggested to have increased the HT1 trap concentration and reduced the HT2 trap concentration. An ∼4dBm improvement in photoresponse under 1.3μm laser excitation and approximately eight times reduction in dark current at −8V reverse bias were attributed to the reduction in the overall trap concentration and mainly the reduction of the AsGa-related midgap trap concentration in the sample grown at 420°C.

Mechanisms of the IR laser initiation of combustion in a supersonic H2/O3/O2 flow

The ignition of a supersonic H2/O3/O2 flow by the λI = 9.7 μm laser excitation of asymmetric vibrations in O3 molecules is considered. The O3 molecules vibrationally excited by laser radiation dissociate more readily to generate active O atoms, thus accelerating the ignition/combustion process. Even at a low input of radiation energy (∼7 × 10−4 J/cm3), combustion in the supersonic flow can be initiated at a short distance (<1 m) from the irradiation zone and at a low gas temperature (∼300 K).

Highly resistive annealed low-temperature-grown InGaAs with sub-500fs carrier lifetimes

We have optimized low-temperature-grown In0.3Ga0.7As for use in ultrafast photoconductive devices. Using low temperature ex situ annealing techniques, we have produced a photoconductive material that is highly resistive (∼104Ωcm), has sub-500fs carrier trapping lifetimes, and is matched to 1.06μm laser excitation.

Terahertz pulsed imaging with 1.06 μm laser excitation

We report the operation of a pulsed terahertz (THz) imaging system that uses a 120 fs pulse-width laser operating at 1.06 μm, and photoconductive InGaAs emitters and detectors. THz images are presented of biological and nonbiological specimens. The signal-to-noise ratio and frequency range of this system are compared to those obtained from existing pulsed imaging systems based on 0.8 μm excitation.

High-quality germanium photodiodes integrated on silicon substrates using optimized relaxed graded buffers

The integration of Ge photodetectors on silicon substrates is advantageous for various Si-based optoelectronics applications. We have fabricated integrated Ge photodiodes on a graded optimized relaxed SiGe buffer on Si. The dark current in the Ge mesa diodes, Js=0.15 mA/cm2, is close to the theoretical reverse saturation current and is a record low for Ge diodes integrated on Si substrates. Capacitance measurements indicate that the detectors are capable of operating at high frequencies (2.35 GHz). The photodiodes exhibit an external quantum efficiency of η=12.6% at λ=1.3 μm laser excitation in the photodiodes. The improvement in Ge materials quality and photodiode performance is derived from an optimized relaxed buffer process that includes a chemical mechanical polishing step within the dislocated epitaxial structure.

Photoluminescence measurements on phosphorus implanted silicon: Annealing kinetics of defects

Room-temperature photoluminescence measurements are performed in order to study the effect of thermal annealing on phosphorus implanted silicon wafers. Measurements are carried out at near band gap excitation with a Nd:YAG laser operating at 1.06 μm. Photoluminescence measurements are also carried out with 0.488 μm laser excitation. It was found that implantation conditions (dose and energy) and annealing temperature strongly influence the intensity of the photoluminescence signal. Contribution from the bulk silicon and the effects from the ion implantation to the photoluminescence signal are discussed.

Novel heptamethine thiapyrylium infrared laser dyes of superior photostability tunable from 1.35 to 1.65 μm

Three new heptamethine thiapyrylium dyes containing a disubstituted amino group on the meso position in their bridged chain were investigated. 4.30 to 5.10% of the pump energy was converted to an intense infrared pulse with wavelength between 1.35 and 1.65 μm. The relation between lasing efficiency and dye concentration was also studied. These dyes show a remarkable photostability upon 1.06 μm laser excitation and excellent storage stability without degassing.

The non-charge transfer mechanism of surface enhanced Raman scattering of pyrazine and methyl viologen adsorbed on Ag and Au electrodes via 1.06 μm laser excitation: a study of bond polarizabilities as elucidated from the Raman intensities

Abstract The surface enhanced Raman scattering (SERS) of pyrazine and methyl viologen on Ag and Au electrodes via 1.06 μm laser excitation is studied through an algorithm which allows the bond polarizabilities to be elucidated from the SERS intensities. It is shown that under 1.06 μm excitation the relative bond polarizabilities of the adsorbates studied are very close to those in solution, suggesting the non-charge transfer process as contrasted with the case under 514.5 μm excitation where those bonds possessing the larger bond orders in HOMO and LUMO have larger bond polarizabilities which is interpreted as the charge transfer process. Various aspects of the non-charge transfer mechanism are discussed along with the response of the bond polarizabilities to the applied voltage on the Ag and Au electrodes. It is also demonstrated that under 1.06 μm excitation, the non-charge transfer process is not always capable of differentiating the otherwise equivalent bonds of the adsorbates due to the adsorption as far as the bond polarizability is concerned, suggesting that the interpretation of the adsorption configuration simply from the spectral appearance is not always correct.

Some Novel Infrared Laser Dyes of Superior Photostability Tunable From 1.30 to 1.52 µm

Three new heptamethine pyrylium dyes containing a disubstituted amino group on the meso position in their bridged chain were investigated. The solutions of the dyes in 1,2‐dichloroethane (DCE) of concentration ca. 10-3 M act as laser dyes transversely pumped by a Q‐switched Nd:YAG laser as a pumping source. 5.6 to 9.6% of the pump energy was converted to an intense infrared pulse with frequencies between 6580 cm-1 (1.52 µm) and 7690 cm-1 (1.30/µm). The relation between lasing efficiency and dye concentration was also studied. These dyes show a remarkable photostability upon 1.06 µm laser excitation and excellent storage stability without degassing.

Electron emission from insulator and semiconductor surfaces by multiphoton excitation below the optical damage threshold

Electron emission due to 1.06 and 0.35 μm laser excitation has been measured at several pulse lengths for a number of wide bandgap semiconductors and insulators. The dependence on fluence and wavelength is consistent with multiphoton excitation across the bandgap. The work functions of the materials investigated do not appear to influence the rate-limiting multiphoton excitation process.

Photoionization transition Cr3+ → Cr2+ in GaAs : Cr

The photoionization absorption spectrum of the strongly Cr-doped GaAs samples was measured in the energy region 5 500-11 000 cm-1 under hydrostatic pressure up to 9 kbar at 300 K and 77 K. The EPR measurements with 1.09 μm laser excitation shows that this absorption is due to the charge transfer Cr3+ → Cr 2+ transitions. The theoretical model which takes into account the lattice relaxation effect is used to fit the photoionization absorption curves. The values of optical ionisation energy EO, thermal ionization energy E T and their pressure dependence are obtained. The relaxation energy ER = EO - ET is found as about 0.17 eV and the absorption cross section as about 5 x 10 -17 cm2.