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 speed ultra short pulse fiber ring laser using photonic crystal fiber nonlinear optical loop mirror

A scheme to generate high speed optical pulse train with ultra short pulse width is proposed and experimentally studied. Two-step compression is used in the scheme: 20 GHz and 40 GHz pulse trains generated from a rational harmonic actively mode-locked fiber ring laser is compressed to a full width at half-maximum (FWHM) of ~ 1.5 ps using adiabatic soliton compression with dispersion shifted fibers (DSF). The pulse trains then undergo a pedestal removal process by transmission through a cascaded two photonic crystal fiber (PCF)-nonlinear optical loop mirrors (NOLM) realized using a double-ring structure. The shortest output pulse width obtained was ~ 610 fs for 20 GHz pulse train and ~ 570 fs for 40 GHz pulse train. The signal to noise ratio of the RF spectrum of the output pulse train is larger than 30 dB. Theoretical simulation of the NOLM transmission is conducted using split-step Fourier method. The results show that two cascaded NOLMs can improve the compression result compared to that for a single NOLM transmission.     

Investigation of optimum condition in oxygen gas-assisted laser cutting

Laser cutting characteristics including power level and cutting gas pressure are investigated in order to obtain an optimum kerf width. The kerf width is investigated for a laser power range of 50–170 W and a gas pressure of 1–6 bar for steel and mild steel materials. Variation of sample thickness, material type, gas pressure and laser power on the average cut width and slot quality are investigated. Optimum conditions for the steel and mild steel materials with a thickness range of 1–2 mm are obtained. The optimum condition for the steel cutting results in a minimum average kerf width of 0.2 mm at a laser power of 67 W, cutting rate of 7.1 mm/s and an oxygen pressure of 4 bar. A similar investigation for the mild steel cutting results in a minimum average kerf width of 0.3 mm at the same laser power of 67 W, cutting rate of 9.5 mm/s, and an oxygen pressure of 1 bar. The experimental average kerf is about 0.3 mm, which is approximately equal to the estimated focused beam diameter of 0.27 mm for our focusing lens (f=4 cm and 100 W power). This beam size leads to a laser intensity of about 1.74×10⁹ W/m² at the workpiece surface. The estimated cutting rate from theoretical calculation is about 8.07 mm/s (1.0 mm thickness and 100 W power), which agrees with the experimental results that is 7.1 mm/s for 1.0 mm thickness of mild steel at the laser power of 88 W.     

A diode end-pumped passively Q-switched Nd:YAG/KTA Raman laser

A diode end-pumped passively Q-switched Nd:YAG/KTA intracavity Raman laser is presented. A KTA crystal with a size of 5 mm × 5 mm × 25 mm is used as the Raman active medium and its 234 cm^?1 Raman mode is employed to finish the conversion from 1064 nm fundamental laser to 1091 nm Raman laser. A 2 mm thick Cr⁴⁺:YAG crystal is used as the saturable absorber. With an LD pump power of 7.5 W, the first-Stokes power of 250 mW is obtained with a pulse repetition frequency of 14.5 kHz. The corresponding diode-to-Stokes conversion efficiency is 3.3% and the pulse energy is 17.2 μJ. Pulse width is measured to be 12.6 ns and peak power is 1.4 kW.     

An anti-reflective 1D rectangle grating on GaAs solar cell using one-step femtosecond laser fabrication

We report the fabrication of the anti-reflective micro/nano-structure on absorbing layer of GaAs solar cell surface using an efficient approach based on one-step femtosecond laser irradiation. Morphology of the microstructures and reflectance of the cell irradiated are characterized with SEM and spectrometer to analyze the influence of laser processing parameters on the change of microstructures induced and the reflectance. It has been found that the rectangle grating micro/nano-structure with a period of 700 nm and width of 600 nm is obtained neatly with laser pulse energy of 30.5 μJ(pulse duration is 130 fs, center wavelength is 800 nm, scanning speed is 2.2 mm/s and spot diameter is 22 µm). Reflectance has been suppressed to 23.6% with rectangle structure from 33% of planar cell. In addition, simulation using a finite-difference-time domain(FDTD) method results show that the rectangle grating micro/nano-structure can effectively suppress the reflection within large wavelength ranges.     

Improvement of stability and pulse energy in a diode-pumped dual-loss-modulated QML Nd:Lu0.2Y0.8VO4 laser with EO modulator and GaAs

The Q-switched and mode-locked (QML) performance in a diode-pumped Nd:Lu_0.2Y_0.8VO₄ laser with electro-optic (EO) modulator and GaAs saturaber absorber is investigated. In comparison with the solely passively QML laser with GaAs, the dual-loss-modulated QML laser with EO and GaAs can generate pulses with higher stability and shorter pulse width of Q-switched envelope, as well as higher pulse energy. At the repetition rate 1 kHz of EO, the pulse width of Q-switched pulse envelope has a compression of 89% and the pulse energy has an improvement of 24 times. The QML laser characteristics such as the pulse width, pulse peak power etc. have been measured for different small-signal transmittance (T₀) of GaAs, different reflectivity (R) of output coupler and modulation frequencies of the EO modulator (f_e). The highest peak power and the shortest pulse width of mode-locked pulses are obtained at f_e = 1 kHz, R = 90% and T₀ = 92.6%. By considering the influences of EO modulator, a developed rate equation model for the dual-loss-modulated QML laser with EO modulator and GaAs is proposed. The numerical solutions of the equations are in good agreement with the experimental results.     

LD-end-pumped passively Q-switched Nd:YAG ceramic laser with single wall carbon nanotube saturable absorber

We report on a LD-end-pumped passively Q-switched Nd:YAG ceramic laser by using a novel single wall carbon nanotube saturable absorber (SWCNT-SA). The SWCNT wafer was fabricated by electric Arc discharge method on quartz substrate with absorption wavelength of 1064 nm. We firstly investigated the continuous wave (CW) laser performance and scattering properties of Nd:YAG ceramic sample. For the case of passively Q-switched operation, a maximum output power of 376 mW was obtained at an incident pump power of 8.68 W at 808 nm, corresponding to an optical–optical conversion efficiency of 4.3%. The repetition rate as the increase of pump power varied from 14 to 95 kHz. The minimum pulse duration of 1.2 μs and maximum pulse energy of 4.5 μJ was generated at a repetition rate of 31.8 kHz.     

Investigation of different surface morphologies formed on AISI 304 stainless steel via millisecond Nd:YAG pulsed laser oxidation

Different surface morphologies on AISI 304 stainless steel have been obtained after millisecond Nd:YAG pulsed laser oxidation. The effects of laser processing parameters, especially pulse width and laser energy density on the surface morphologies of the stainless steel were emphatically investigated. The results showed that surface morphologies were significantly changed with increasing laser pulse widths and laser energy densities. When the pulse width was 0.2–1.0 ms and laser energy density was 4.30×10⁶–7.00×10⁶ J/m², the surface was obviously damaged and the morphologies varied gradually from craters to ripple structures. However, when the pulse width was longer than 1 ms and the laser energy density was increased from 1.90×10⁷ to 3.16×10⁷ J/m², the sizes of craters got smaller until disappeared and the surface became flatter and smoother. Nevertheless, the smooth surface was not obtained under overhigh laser energy densities. In addition, the schematic relationship was used to describe the formation process and mechanism of different surface morphologies.     

330 MHz,sub 50 fs Yb: Fiber ring laser

We demonstrate 330 MHz repetition rate operation in a ring cavity Yb:fiber laser with an innovative wavelength-division-multiplexing collimator to raise the repetition rate. The spectral bandwidth of the pulse is 30 nm and the dechirped pulse width is 48 fs. The output power is 70 mW with 600 mW, 975 nm pump laser diode.     

Optimization of laser welding of DP/TRIP steel sheets using statistical approach

Generally, the quality of a weld joint is directly influenced by the welding input parameter settings. Selection of proper process parameters is important to obtain the desired weld bead profile and quality. In this research work, numerical and graphical optimization techniques of the CO₂ laser beam welding of dual phase (DP600)/transformation induced plasticity (TRIP700) steel sheets were carried out using response surface methodology (RSM) based on Box–Behnken design. The procedure was established to improve the weld quality, increase the productivity and minimize the total operation cost by considering the welding parameters range of laser power (2–2.2 kW), welding speed (40–50 mm/s) and focus position (?1 to 0 mm). It was found that, RSM can be considered as a powerful tool in experimental welding optimization, even when the experimenter does not have a model for the process. Strong, efficient and low cost weld joints could be achieved using the optimum welding conditions.     

Weld-bead profile and costs optimisation of the CO2 dissimilar laser welding process of low carbon steel and austenitic steel AISI316

The dissimilar full depth laser-butt welding of low carbon steel and austenitic steel AISI 316 was investigated using CW 1.5 kW CO₂ laser. The effect of laser power (1.1–1.43 kW), welding speed (25–75 cm/min) and focal point position (?0.8 to ?0.2 mm) on the weld-bead geometry (i.e. weld-bead area, A; upper width, W_u; lower width, W_l and middle width, W_m) and on the operating cost C was investigated using response surface methodology (RSM). The experimental plan was based on Box–Behnken design; linear and quadratic polynomial equations for predicting the weld-bead widthness references were developed. The results indicate that the proposed models predict the responses adequately within the limits of welding parameters being used. The regression equations were used to find optimum welding conditions for the desired geometric criteria.     

An experimental study of an acousto-optic Q-switched Yb3+-doped all-fiber laser

The Q-switched fiber lasers are very attractive sources in many applications such as military affairs, surgical operation, laser machining, laser marking, nonlinear frequency conversion, range finding, remote sensing and optical time domain reflectometer. In this paper, an acousto-optic Q-switched Yb³⁺-doped all-fiber laser at 1083 nm is reported. The pulse energy of 2.94 mJ has been obtained at the pump power of 8.47 W, and the pulse width is 3 μs.     

Nanosecond-pulsed erbium-doped fiber lasers with graphene saturable absorber

We demonstrate graphene mode-locked nanosecond erbium-doped fiber laser in an all-fiber ring cavity. The clean and robust pulse train was generated at 27 mW pump power. Resultant central wavelength, repetition rate and pulse width was 1560 nm, 388 kHz and 6 ns, respectively. With two stage fiber amplifier, the output power was 553 mW, corresponding to single pulse energy of 1.4 μJ. In addition, the pulse-width can be varied ranging from 3 ns to 20 ns at repetition rate between 200 kHz and 1.54 MHz by changing the length of the laser cavity.     

A study of the influence of the input electrical power on the spectral width of the 510.6 nm line of an atomic copper vapor laser

The effect of the input electrical power on the spectral width of the 510.6 nm line of an atomic copper vapor laser (CVL) is investigated. An analysis of the gas temperature inside the discharge tube and the line broadening mechanism of the CVL is reported. The input electrical power was varied from 2.0 to 4.2 kW in a cylindrical discharge tube of inner radius 2.35 cm and length 150.0 cm. A Fabry–Perot etalon and imaging camera-based setup interfaced with personal computer was used to measure the spectral width of the 510.6 nm (green) laser line. The Doppler broadened spectral profile of the laser emission varies with input electrical power and an additional broadening of almost 1 GHz at the highest operating input power was observed.     

Laser diode end-pumped passively Q-switched Tm,Ho:YLF laser with Cr:ZnS as a saturable absorber

Output performance of a continuous-wave (CW) laser diode end-pumped passively Q-switched Tm,Ho:YLF laser is demonstrated with a Cr:ZnS crystal as the saturable absorber. We particularly investigate the influence of saturable absorber's position in the resonator when the Cr:ZnS crystal is placed close to and far from the laser beam waist. We compare the experimental results at the two different positions, and find that the laser shows unusual output characteristics when the Cr:ZnS saturable absorber is placed close to the beam waist. The pulse width and the pulse energy almost keep constant, measured about 1.25 μs and 4 μJ respectively, when the pump power is changed in the range of 1–1.9 W. Moreover, the pulse repetition frequency can be tuned between 1.3 kHz and 2.6 kHz by changing the pump power. The output wavelength of the passively Q-switched laser shifts to 2053 nm from 2067 nm in CW operation.     

Efficient end-pumped Q-switched 1053 nm Nd:YLF laser with a plane-parallel resonator

In this study, a compact and efficient Nd:YLF laser at 1053 nm has been reported without inserting optical intracavity element to suppress the stronger line of 1047 nm. According to theoretical analysis and calculation, the thermal focal length of 1047 nm is negative while that of 1053 nm is positive in plane-parallel resonator. Hence 1053 nm laser was stable in this cavity. In our experiment, 7.5 W laser output at σ-polarized 1053 nm has been obtained with optical–optical efficiency of 38.8%. As the pulse repetition rate is 20 kHz, the pulse width is 50 ns and the peak power is calculated to be 7.5 kW.     

Diode-pumped doubly Q-switched Nd:Lu0.33Y0.37Gd0.3VO4 laser with an electro-optic modulator and a single-walled carbon nanotube saturable absorber

By simultaneously using an electro-optic (EO) modulator and a single-walled carbon nanotube saturable absorber (SWCNT-SA) in the cavity, a diode-pumped doubly Q-switched Nd:Lu_0.33Y_0.37Gd_0.3VO₄ (Nd:LuYGdVO₄) laser is demonstrated. At the incident pump power 11.43 W and f=2 kHz, the minimum pulse width 17.6 ns and the maximum pulse peak power 19,886 W can be obtained. The experimental results show that this doubly Q-switched Nd:LuYGdVO₄ laser can generate shorter pulse width and higher peak power compared to the singly Q-switched Nd:LuYGdVO₄ laser with only EO or SWCNT-SA.     

High pulse repetition frequency RF excited waveguide CO2 laser with mechanical Q-switching

In this paper, a mechanical Q-switching is used in radio frequency (RF) excited waveguide CO₂ laser to obtain high pulse repetition frequency (PRF) laser. The Q-switching system includes two confocal ZnSe lenses and a high speed mechanical chopper, which is inserted into the cavity. The peak power is up to 730 W and the pulse width 200 ns at the highest PRF 20 kHz. The laser also has the advantages of compact, small-volume, and low-cost.     

High-energy dissipative soliton with MHz repetition rate from an all-fiber passively mode-locked laser

We experimentally demonstrate pulse energy enhancement in an all-fiber passively mode-locked laser operating in the large normal dispersion regime. By increasing the laser cavity length as well as its net cavity dispersion, the proposed laser, which is mode-locked by nonlinear polarization rotation, generates highly chirped dissipative solitons with pulse energies up to 9.4 nJ. The fundamental repetition rate is 2.3 MHz, and the pulse duration is 35 ps. Such low repetition rate as well as wide pulse width makes this mode-locked all-fiber laser a suitable oscillator to directly seed a fiber amplifier, which can be used as compact sources for high-power applications.     

Femtosecond laser processing of indium-tin-oxide thin films

Micro- and nano-scale crystalline indium-tin-oxide (c-ITO) patterns fabricated from amorphous ITO (a-ITO) thin films on a glass substrate using a (low NA 0.26) femtosecond laser pulse that is not tightly focused are demonstrated. Different types of c-ITO patterns are obtained by controlling the laser pulse energies and pulse repetition rate of a femtosecond laser beam at a wavelength of 1064 nm: periodic micro c-ITO dots with diameters of ~1.4 μm, two parallel c-ITO patterns with/without periodic-like glass nanostructures at a laser scanning path and nano-scale c-ITO line patterns with a line width ~900 nm, i.e. ~1/8 of the focused beam׳s diameter (7 μm at 1/e²).