Design and construction of Q-switched Nd:YAG laser system for LIBS measurements

A passive, Q-switched pulsed, Nd:YAG laser system was designed and built, which can provide a potential compact robust laser source for portable laser induced breakdown spectroscopy systems.The developed laser system operates at 1064 nm. Each laser shot contains a train of pulses having maximum total output energy of 170 mJ. The number of pulses varies from 1–6 pulses in each laser shot depending on the pump energy. The pulse width of each pulse ranges from 20 to 30 ns. The total duration of the output pulse train is within 300 μs. The multi-pulse nature of the laser shots was employed to enhance the LIBS signal. To validate the system, LIBS measurements and analysis were performed on ancient ceramic samples collected from Al-Fustat excavation in Old Cairo. The samples belong to different Islamic periods in Egypt history. The results obtained are highly indicative that useful information can be provided to archeologists for use in restoring and repairing of precious archeological objects.     

High resolution scanning microanalysis on material surfaces using UV femtosecond laser induced breakdown spectroscopy

Femtosecond lasers together with high resolution optics have given us the ability to achieve submicron ablation spots which can play an important role in specific micromachining applications. Light emitted from the plasma at the sample surface created by a focused femtosecond laser pulse can also be used in laser induced breakdown spectroscopy (LIBS) and allows us to characterize the chemical composition of the target surface with micron-level lateral resolution. The spatial resolution using LIBS has often been defined by measuring the FWHM of the crater size. In this report, we study the application of femtosecond 266 nm laser pulses with very low energies of 10׳s of nanojoules. We have investigated spatial resolution using the detection of thin strips of chromium on silicon substrates and compared the actual width of the chromium versus the experimentally obtained width using LIBS detection. The variation of signal levels for low pulse energies is investigated on chromium surfaces. A spatial resolution of ~1 μm was obtained for detection of chromium from the emission.     

Dual frequency cavitation event sensor with iodide dosimeter

The inertial cavitation activity depends on the sonication parameters. The purpose of this work is development of dual frequency inertial cavitation meter for therapeutic applications of ultrasound waves. In this study, the chemical effects of sonication parameters in dual frequency sonication (40 kHz and 1 MHz) were investigated in the progressive wave mode using iodide dosimetry. For this purpose, efficacy of different exposure parameters such as intensity, sonication duration, sonication mode, duty factor and net ultrasound energy on the inertial cavitation activity have been studied. To quantify cavitational effects, the KI dosimeter solution was sonicated and its absorbance at a wavelength of 350 nm was measured. The absorbance values in continuous sonication mode was significantly higher than the absorbance corresponding to the pulsed mode having duty factors of 20–80% (p < 0.05). Among different combination modes (1 MHz_100% + 40 kHz_100%, 1 MHz_100% + 40 kHz_80%, 1 MHz_80% + 40 kHz_100%, 1 MHz_80% + 40 kHz_80%), the continuous mode for dual frequency sonication is more effective than other combinations (p < 0.05). The absorbance for this combined dual frequency mode was about 1.8 times higher than that obtained from the algebraic summation of single frequency sonications. It is believed that the optimization of dual frequency sonication parameters at low-level intensity (<3 W/cm²) by optically assisted cavitation event sensor can be useful for ultrasonic treatments.     

A ppb level sensitive sensor for atmospheric methane detection

A high sensitivity sensor, combining a multipass cell and wavelength modulation spectroscopy in the near infrared spectral region was designed and implemented for trace gas detection. The effective length of the multipass cell was about 290 meters. The developed spectroscopic technique demonstrates an improved sensitivity of methane in ambient air and a relatively short detection time compared to previously reported sensors. Home-built electronics and software were employed for diode laser frequency modulation, signal lock-in detection and processing. A dual beam scheme and a balanced photo-detector were implemented to suppress the intensity modulation and noise for better detection sensitivity. The performance of the sensor was evaluated in a series of measurements ranging from three hours to two days. The average methane concentration measured in ambient air was 2.01 ppm with a relative error of ± 2.5%. With Allan deviation analysis, it was found that the methane detection limit of 1.2 ppb was achieved in 650 s. The developed sensor is compact and portable, and thus it is well suited for field measurements of methane and other trace gases.     

Temperature sensing performance of dysprosium doped aluminum oxide powders

Dy³⁺-doped Al₂O₃ powders were prepared by combustion synthesis. Down-converted luminescence lines peaked at 451 and 471, 572, 660, 708 and 752 nm were obtained under 355 nm pulsed laser irradiation for as-prepared Dy³⁺ doping concentrations of 0.5, 1.0 and 2.0 wt.%. The fact that the relative intensities of the 451 and 471 nm luminescence bands changed with the samples temperature allowed the use of these emission lines for temperature sensing. We found that the maximum sensitivity of the temperature sensor based on the luminescence intensity ratio of those transitions changed with Dy³⁺ doping concentration indicating different coupling strengths between the crystal field and the rare-earth.     

Determination of Ca content of coral skeleton by analyte additive method using the LIBS technique

Laser-induced breakdown spectroscopic (LIBS) technique was used to study the elemental pro?le of coral skeletons. Apart from calcium and carbon, which are the main elemental constituents of coral skeleton, elements like Sr, Na, Mg, Li, Si, Cu, Ti, K, Mn, Zn, Ba, Mo, Br and Fe were detected in the coral skeletons from the Inani Beach and the Saint Martin’s island of Bangladesh and the coral from the Philippines. In addition to the qualitative analysis, the quantitative analysis of the main elemental constituent, calcium (Ca), was done. The result shows the presence of (36.15±1.43)% by weight of Ca in the coral skeleton collected from the Inani Beach, Cox’s Bazar, Bangladesh. It was determined by using six calibration curves, drawn for six emission lines of Ca I (428.301 nm, 428.936 nm, 431.865 nm, 443.544 nm, 443.569 nm, and 445.589 nm), by standard analyte additive method. Also from AAS measurement the percentage content of Ca in the same sample of coral skeleton obtained was 39.87% by weight which compares fairly well with the result obtained by the analyte additive method.     

Inherently gain flattened S-band erbium doped fiber amplifier based on dual core resonant leaky fiber

A co-axial dual core resonant leaky optical fiber (DCRLF) is designed for inherent gain equalization of S-band erbium doped fiber amplifier (EDFA). Resonance tail of leakage loss of the fiber into the S-band region is utilized to flatten the gain. We have numerically studied the effect of various design parameters and their fabrication tolerances on gain flattening. We show 23.5 dB flat gain with ± 0.9 dB ripple over 30 nm bandwidth (1490–1520 nm) using 120 mW pump. The study should be useful in designing optical fiber amplifiers for optical communication system employing wavelength division multiplexing.     

Femtosecond laser ablation of cadmium tungstate for scintillator arrays

Ultrafast pulsed laser ablation has been investigated as a technique to machine CdWO₄ single crystal scintillator and segment it into small blocks with the aim of fabricating a 2D high energy X-ray imaging array. Cadmium tungstate (CdWO₄) is a brittle transparent scintillator used for the detection of high energy X-rays and γ-rays. A 6 W Yb:KGW Pharos-SP pulsed laser of wavelength 1028 nm was used with a tuneable pulse duration of 10 ps to 190 fs, repetition rate of up to 600 kHz and pulse energies of up to 1 mJ was employed. The effect of varying the pulse duration, pulse energy, pulse overlap and scan pattern on the laser induced damage to the crystals was investigated. A pulse duration of ≥500 fs was found to induce substantial cracking in the material. The laser induced damage was minimised using the following operating parameters: a pulse duration of 190 fs, fluence of 15.3 J cm⁻² and employing a serpentine scan pattern with a normalised pulse overlap of 0.8. The surface of the ablated surfaces was studied using scanning electron microscopy, energy dispersive X-ray spectroscopy, atomic force microscopy and X-ray photoelectron spectroscopy. Ablation products were found to contain cadmium tungstate together with different cadmium and tungsten oxides. These laser ablation products could be removed using an ammonium hydroxide treatment.     

11-mJ pulse energy wideband Yb-doped fiber laser

We report a wide bandwidth (Δλ=8 nm) optical pulsed MOPA (master oscillator power amplifier) source emitting 11.23 mJ pulses (1.25 MW peak power) in the wavelength centered at (λ=1064 nm). Pulse duration and repetition rate were 9 ns and from 10 Hz to 100 Hz, respectively. In order to suppress amplified spontaneous emission (ASE), multi-stage pulse pump technology is applied. And the large core diameter (90 μm) and wide bandwidth ensures the high peak power and energy output.     

Large-range liquid level sensor based on an optical fibre extrinsic Fabry–Perot interferometer

We propose an efficient approach to develop large-range liquid level sensors based on an extrinsic Fabry–Perot optical fibre interferometer with an all fused-silica structure and CO₂ laser heating fusion bonding technology. The sensor exhibits signatures of a high sensitivity of 5.3 nm/kPa (36.6 nm/psi), a resolution of 6.8 Pa (9.9×10⁻⁴ psi) and an extreme low temperature dependence of 0.013 nm/°C. As a result, a high resolution of the water level measurement of approximately 0.7 mm on the length scale of 5 m and small errors of the water pressure measurement induced by the temperature dependence within 0.0025 kPa/°C (0.00036 psi/°C, water level 0.25 mm/°C) are achieved, thus providing useful applications for the detection of the large-range liquid level in harsh environments.     

Texture and strain in CoPt/Ag nanocomposite films

The texture and microstrain in CoPt/Ag nanocomposite films is monitored as a function of film thickness. Perpendicular anisotropy due to (0 0 1) texturing is achieved by annealing films with thickness below 15 nm at 600°C. As a function of film thickness δ the texture evolves from weak (0 0 1) below 9 nm to strong (0 0 1) at δ=12 nm which deteriorates rapidly above 15 nm and evolves to (1 1 1) above 40 nm. The strain is minimized in the range of film thickness where the (0 0 1) texturing is optimum indicating a texturing mechanism related to the reduction of mechanical strain energy.     

Experimental study on tandem pumped fiber amplifier

We present the experimental results of a 1083 nm fiber amplifier tandem pumped by 1030 nm fiber laser. The output characteristics of the tandem pumped amplifier with cladding-pump and core-pump schemes are both investigated. The 1083 nm signal laser has not been efficiently amplified when cladding-pumped by 1030 nm laser for the weak absorption of the gain fiber. The core-pump scheme works well with the amplifier. The output properties with different gain fiber length are experimentally investigated. The maximum output power is 2.4 W with power conversion efficiency of 60%.     

Properties of a gold-deposited surface plasmon resonance-based glass rod sensor with various light-emitting diodes and its application to a refractometer

The performance of a simple sensor system prepared using gold (Au)-deposited glass rods of 1 to 4 mm in diameter with a deposition length of 100 mm based on surface plasmon resonance (SPR) is presented. The sensor properties of the Au-deposited glass rods of 2 mm in diameter with deposition lengths of 10 to 100 mm are also presented. The sensor system consists of a light-emitting diode (LED) as the light source and a photodiode (PD) as the detector. The response curves and sensor properties of the Au-deposited glass rod with a Au film thickness of 45 nm obtained by using three LEDs with yellowish green (563 nm), red (660 nm), and infrared (940 nm) emissions were investigated. The results were compared with those of a corresponding Au-deposited optical fiber sensor with a core diameter of 0.2 mm. Though the sensitivity, response, and detection limit of the Au-deposited glass rod sensor are lower than those of the optical fiber sensor, the fabrication and handling of the Au-deposited glass rod sensor are easier because of the robustness. Since the dielectric constant of Au changes with the light wavelength, the sensor properties of both the Au-deposited glass rod sensor and the optical fiber sensor depend strongly on the wavelength of the incident light and can be controlled by changing the LED emission wavelength. This sensor system is a new SPR-based refractometer with easy construction and operation. Ethanol concentrations in various spirits were measured with this SPR-based refractometer and the results agreed well with those measured with an Abbe refractometer.     

Enhancement of magnetic properties of Co/Pd multilayered perpendicular magnetic recording media by using Pd/Si dual seedlayer

Effects of the introduction of a Pd/Si dual seedlayer on the microcrystalline structure and magnetic properties of [Co/Pd]_n multilayered perpendicular magnetic recording media were investigated. The Pd/Si dual seedlayer was composed of a Pd upper seedlayer and a Si under seedlayer. The Pd upper seedlayer with a thickness of up to 10 nm markedly increased the coercivity of [Co/Pd]_n multilayered media in the direction perpendicular to the film surface. The highest coercivity of 7.8 kOe was obtained for the [Co/Pd]₁₀ medium with a Pd (10 nm)/Si (100 nm) dual seedlayer. The Pd upper seedlayer not only facilitated the formation of regular interfaces between the Co and Pd layers, but also reduced the thickness of the deteriorated initial layer in the [Co/Pd]_n multilayer, resulting in enhancement of the magnetic anisotropy field. The [Co/Pd]_n multilayered medium with the Pd/Si dual seedlayer exhibited weak intergranular exchange coupling between [Co/Pd]_n grains, which led to excellent read–write characteristics.     

Hydrogen permeation of tungsten phosphate glass thin films

Thin films of tungsten phosphate glasses were deposited on a Pd substrate by a pulsed laser deposition method and the flux of hydrogen passed thorough the glass film was measured with a conventional gas permeation technique in the temperature range 300–500 °C. The glass film deposited at low oxygen pressure was inappropriate for hydrogen permeation because of reduction of W ions due to oxygen deficiency. The membrane used in the hydrogen permeation experiment was a 3-layered membrane and consisted of Pd film (~ 20 nm), the glass film (≤ 300 nm) and the Pd substrate (250 µm). When the pressure difference of hydrogen and thickness of the glass layer were respectively 0.2 MPa and ~ 100 nm, the permeation rate through the membrane was 2.0 × 10^? 6 mol cm^? 2 s^? 1 at 500 °C. It was confirmed that the protonic and electronic mixed conducting glass thin film show high hydrogen permeation rate.     

Influence of argon ambience on the structural,morphological and optical properties of pulsed laser ablated zinc sulfide thin films

Nanostructured zinc suplhide thin films are successfully deposited on quartz substrates using pulsed laser deposition (PLD) under different argon pressures (0, 5, 10, 15 and 20 Pa). The influence of argon ambience on the microstructural, optical and luminescence properties of zinc sulfide (ZnS) thin films is systematically investigated. The GIXRD data suggests rhombohedral structure for ZnS films prepared under different argon ambience. Self-assembly of grains into well-defined patterns along the y direction is observed in the AFM image of the film deposited under argon pressure 20 Pa. All the films show a blue shift in optical band gap. This can be due to the quantum confinement effect and less widening of conduction and valence band for the films with less thickness and smaller grain size. The PL spectra of the different films are recorded at excitation wavelengths 250 nm and 325 nm and the spectra are interpreted. The PL spectra of the films recorded at excitation wavelength 325 nm show intense yellow emission. The film deposited under an argon pressure of 15 Pa shows the highest PL intensity for excitation wavelength 325 nm. For the PL spectra (excitation at 250 nm), the highest PL intensity is observed for the film prepared under argon free ambience. In our study, 15 Pa is the optimum argon pressure for better crystallinity and intense yellow emission when excited at 325 nm.     

Second-harmonic laser-coupled optical fiber sensor for pH measurement and corrosion detection based on evanescent field absorption

In the present paper, a laser-coupled optical fiber is introduced for pH sensing of Methyl red solution in the Ethanol solvent. Then it is modified for corrosion detection when it was placed inside a corrosive solution. Second-harmonic (SH) radiation of a microchip Q-switched pulsed Nd:YAG laser operating at λ=532 nm is generated via KTP nonlinear crystal, and it is launched into the fabricated fiber sensor. The provided evanescent field is absorbed by the surrounding environment in the sensing region, and the output intensity of the absorbed laser beam is monitored and recorded in the presence of the different kind of solvents and corrosive solutions. To increase the sensitivity of the pH sensor the fiber-optic probe is coiled and fixed on a Poly Propylene (PP) mount with 6 cm diameter and 10 cm long. The fabricated sensor is then calibrated for pH measurement of unknown media. For corrosion detection, a spin motor is used to uniformly coat a small portion of the fiber designed as U-shaped after its clad was removed by a simple chemical method. It is then electroplated by a very thin Fe–C film to form a corrosion sensor. It is observed that while the concentration of the NH₄Cl solution is changed from 0.068 to 0.125 mol/l and its pH from zero to 14, the output intensity of the launched laser is increased due to the Fe–C film corrosion.     

Absorption spectra response of XRQA radiochromic film to x-ray radiation

Gafchromic XRQA, radiochromic film is a high sensitivity auto developing x-ray analysis films designed and available for kilovoltage x-ray, dose and QA assessment applications. The film is designed for reflective analysis with a yellow transparent top filter and white opaque backing materials. This allows the film to be visually inspected for colour changes with a higher level of contrast than clear coated radiochromic films such as Gafchromic EBT version 1. The spectral absorption properties in the visible wavelengths have been investigated and results show two main peaks in absorption located at 636 nm and 585 nm. These peaks are located in the same position as EBT Gafchromic film highlighting a similar chemical monomer/polymer for radiation sensitivity. A much higher sensitivity however is found at kilovoltage energies with an average 1.55 OD units per 20 cGy irradiation variation measured at 636 nm using 150 kVp x-rays. This is compared to approximately 0.12 OD units per 20 cGy measured at 636 nm for EBT film at 6 MV x-ray energy. That is, the XRQA film is more than 10 times more sensitive than EBT1 film. The visual colour change is enhanced by the yellow polyester coating. However this does not affect the absorption spectra properties in the red region of analysis which is the main area for use using desktop scanners in reflection mode.     

Arrayed waveguide grating-based demultiplexer with two central wavelengths

In this paper we have presented an arrayed waveguide grating with two central wavelengths, 1550.12 nm and 1310.12 nm. Introducing a novel architecture for outputs of system, if input light to arrayed waveguide grating consists of wavelengths around 1550.12 nm, proposed system will act as 16 channels demultiplexer with channel spacing of 1.6 nm. On the other hand when input wavelengths are distributed around 1310.12 nm, the same arrayed waveguide grating will divide the input to 27 channels with channel spacing of 0.68 nm.