Laser-diode-pumped passively Q-switched Nd:YVO4 green laser with periodically poled KTP and GaAs saturable absorber

A laser-diode-pumped passively Q-switched Nd:YVO₄ green laser with periodically poled KTP (PPKTP) and GaAs saturable absorber has been realized. The dependences of pulse repetition rate, pulse energy, pulse width and peak power on incident pump power for the generated-green-light pulses are measured. At the maximum incident pump power of 4.1 W, the maximum average output power of 113 mW is obtained, corresponding to an optical conversion efficiency of 2.8%. At the same pump power, stable green laser pulses of duration of 44.6 ns and energy of 0.28 µJ are generated at a repetition rate of 403.4 kHz. The coupling wave rate equations for a passively Q-switched laser are also given and the numerical solutions agree with the experimental results.     

High-peak-power, pulsed CO(2) laser light delivery by hollow glass waveguides

Flexible hollow glass waveguides with internal metallic and dielectric coatings have been used to deliver high-peak-power transversely excited atmosphere CO(2) laser energy. The straight guide loss is as low as 0.17 dB/m for 1000-mum-bore guides and 0.46 dB/m for 530-mum-bore guides propagating the HE(11) mode. The loss increases to 0.93 and 1.36 dB/m, respectively, when guides are bent to a radius of 0.25 m. The hollow glass waveguides have been used to deliver pulsed CO(2) laser energy successfully with a peak power of 0.7 MW and an energy of 350 mJ per pulse with a gas purge through the hollow core. The delivered average power is as high as 27 W. It is concluded that these waveguides are promising candidates for pulsed CO(2) laser delivery in medical and surgical applications.     

Passively Q-switched fibre laser utilizing erbium-doped fibre saturable absorber for operation in C-band region

In this paper, a stable and robust all-fibre passively Q-switched erbium-doped fibre laser (EDFL) emitting at 1558?nm is described. The proposed laser utilizes an 11?cm long erbium-doped fibre as saturable absorber (SA). The fibre SA features a linear optical absorption of about 13?dB in the Q-switched EDFL operating regime. By elevating the input pump power from the threshold of 60?mW to the maximum available power of 142?mW, a pulse train with a maximum repetition rate of 86?kHz, minimum pulse width of 3.39?µs, maximum average output power of 10.5?mW, maximum pulse energy of 122?nJ and maximum peak power of 36?mW are obtained. The signal to noise ratio (SNR) of the spectrum is measured to be around 70?dB. This fibre SA is simple, reliable, compact and alignment free. Thus it is suitable for making a portable pulse laser source.     

Pulse shaping fiber laser at 1.5 μm

In this paper we present, for the first time to our knowledge, a new pulse shaping technology (modulation schemes for seed laser) used to mitigate pulse narrowing effect and SBS effect in a high energy Er:Yb codoped fiber master oscillator power amplifier system at 1.5 μm to obtain longer pulse duration and higher energy. An average power of over 1.3 W and a pulse energy of over 0.13 mJ were obtained at 10 kHz repetition rate with a pulse duration of 200 ns and near-diffraction-limited beam quality (M(2)<1.2).     

Development of a compact and reliable repetitively pulsed Xe Cl (308 nm) excimer laser

Development and operation characteristics of a repetitively pulsed UV spark pre-ionized XeCl (Xenon Chloride) excimer laser is described. The laser uses discharge pumped C–C charge transfer excitation. A compact gas circulation loop was adopted to achieve high repetition rate operation. The laser generates optical pulses of energy 150 mJ at 150 Hz reliably. The electrical to optical conversion efficiency obtained is 1%. The laser pulse duration is ~8 nS (FWHM). The single fill gas lifetime have been found to be 2 × 10⁶ shots for 20% reduction of energy without any halogen injection. The system is compact and reliable.     

Yb:S-FAP lasers

It has recently been reported that several high power, diode-pumped laser systems have been developed based on crystals of Yb:S-FAP [Yb³⁺:Sr₅(PO₄)₃F]. The mercury laser, at Lawrence Livermore National Laboratory, is the most prominent system using Yb:S-FAP and is currently producing 23 J at 5 Hz in a 15 nsec pulse, based on partial activation of the system. In addition, a regenerative amplifier is being developed at Waseda University in Japan and has produced greater than 12 mJ with high beam quality at 50 Hz repetition rate. Q-Peak has demonstrated 16 mJ of maximum energy/output pulse in a multi-pass, diode side-pumped amplifier and ELSA in France is implementing Yb:S-FAP in a 985 nm pump for an EDFA, producing 250 mW. Growth of high optical quality crystals of Yb:S-FAP is a challenge due to multiple crystalline defects. However, at this time, a growth process has been developed to produce high quality 3.5 cm diameter Yb:S-FAP crystals and a process is under development for producing 6.5 cm diameter crystals.     

500 Hz ultraviolet dye laser with pulse energy 1.7 mJ and potential for PLIF imaging

ABSTRACT

This paper describes a high-pulse-energy frequency-doubled ultraviolet dye laser operating at a repetition rate of 500?Hz. The pump source is a laser-diode side-pumped Q-switched Nd:YAG laser with a pulse energy of 29?mJ at 532?nm. A master oscillator power amplifier is employed to amplify the output pulse of the dye laser to 8.1?mJ at 566?nm, and by frequency doubling with BBO crystal a pulse energy of 1.7?mJ at 283?nm is achieved with a pulse width of 8?ns. This is more than four times the largest reported pulse energies generated by other fixed-frequency dye lasers when operating at repetition rates of more than 1?kHz. The conversion efficiency and stability of dye laser are discussed, which show the potential for high-speed laser diagnostics in the fields of combustion and turbulent flow detection.     

On the possibility of increasing the efficiency of sealed-off nitrogen lasers

A sealed-off nitrogen laser operating in a periodic-pulse regime at a repetition rate of 40 Hz has been experimentally studied and it is demonstrated that the laser efficiency can be increased by quasi-stationary energy pumping into the active medium (pure nitrogen or its mixtures with helium or neon). The presence of a buffer gas (helium or neon) allows the energy parameters of radiation to be increased and the laser efficiency to be controlled. A small-sized sealed-off nitrogen laser is developed, which operates at a peak output power of 160 kW and a pulse energy of 0.8 mJ with an efficiency of 0.27%.     

Deep ablation and depth profiling by laser-induced breakdown spectroscopy (LIBS) employing multi-pulse laser excitation: application to galvanized steel

The potential of a multi-pulse (MP) laser excitation scheme for deep stratigraphy of electrolytically galvanized steel using laser-induced breakdown spectrometry (LIBS) has been evaluated. For this purpose, a commercial electro-optically (EO) Q-switched Nd:YAG laser was employed, where by reducing the delay between the Q-switch opening and the flash lamp, a train of pulses (up to 11) separated by approximately 7.40 μs was generated during one lamp flashing. Plasma emission after each individual laser pulse of the MP sequence was detected by a spectrograph equipped with an intensified charge-coupled device (iCCD) detector. With MP excitation, the ablation efficiency was increased ten-fold on iron sample and 22.5-fold on zinc material with respect to dual-pulse or single-pulse excitation. The LIBS signal generated by MP excitation shows an analogous enhancement. Although the total energy per shot delivered to samples was only 60 mJ, it was possible using LIBS to measure the sample stratigraphy up to depths of 90 μm on zinc-coated steel sheets. A satisfactory agreement between the Zn thickness determined by the MP-LIBS system and data from the manufacturer has also been obtained.     

Nickel oxide nanoparticles thin film saturable absorber for 1-micron pulsed all-fibre lasers operation

A passive Q-switched and mode-locked ytterbium-doped fibre laser (YDFL) pulse generation using a nickel oxide thin film as a saturable absorber is reported. The nickel oxide nanoparticle thin film was fabricated by a simple processing technique, and it has a modulation depth of 39% and saturation intensity of 0.04 MW/cm². The saturable absorber was constructed by inserting a small piece of the film between two fibre ferrules. Then it was integrated in a YDFL cavity. The Q-switching operation started at a threshold pump power of 117.73 mW with an initial wavelength of 1073.5 nm. When the pump power was raised from 117.73 to 133 mW, the repetition rate grew from 9.5 to 15.8 kHz. The pulses had a maximum pulse energy of 478 nJ. Furthermore, a stable self-started mode-locked pulse was also succesfully generated at the threshold pump power of 97.3 mW. The central wavelength and repetition rate of the laser were 1037.72 nm and 23 MHz, respectively. The maximum pulse energy of 0.56 nJ and a peak power of 26.4 W were recorded at a pump power of 137.5 mW.     

Dual-wavelength self-Q-switched Nd:GYSGG laser

A dual-wavelength self-Q-switched operation of Nd:GYSGG laser with different output couplers is proposed and demonstrated. In self-Q-switched operation, two laser lines between 1056.86 nm and 1060.23 nm were found. Under the pump power of 4 W, the shortest pulse width of 2.02 μs was obtained with a maximum average output power of 565 mW and the optical conversion efficiency of 14.13%. The pulse repetition rate and single pulse energy were 50.2 kHz and 11.25 μJ, respectively. The system is very stable and suitable for generation of multi-wavelength pulses.     

Passively mode-locked Yb3+:Sc2SiO5 laser with reflection-type single-walled carbon nanotube absorber

A reflection-type single-walled carbon nanotube saturable absorber fabricated by a vertical evaporation method was to our knowledge first used in a passively mode-locked Yb(3+):Sc(2)SiO(5)(Yb:SSO) laser. The laser operated at a repetition frequency of 94 MHz with a central wavelength of 1062.6 nm. A short pulse duration of 1.8 ps was produced with an average power of 349 mW; and the highest pulse energy of 3.7 nJ, corresponding to its maximum peak power, can reach 2.1 kW.     

Cavity-length optimization for high energy pulse generation in a long cavity passively mode-locked all-fiber ring laser

In order to achieve higher pulse energy in a passively mode-locked fiber ring laser, a long cavity length is commonly implemented. However, a long cavity operating in the anomalous dispersion regime also leads to pulse broadening, which reduces the average pulse power. In this paper, the trade-off between cavity length and average pulse power is investigated with the aim of optimizing the cavity length to achieve maximum pulse energy. Numerical simulation results, presented here, indicate that there exists an optimum cavity length for which the pulse energy is maximum and the optimum length shifts as the pump power changes. The simulation results for a pump power of 500 mW are verified by measurements carried out on a long cavity nonlinear polarization rotation mode-locked all-fiber ring laser operating in the anomalous dispersion regime. With a repetition rate of 266 kHz for the dissipative solitons, we achieve a pulse energy of 139.1 nJ for a cavity length of 700 m. Higher pulse energy can be expected by using a pump laser diode with higher pump power.     

MEH-PPV organic material as saturable absorber for Q-switching and mode-locking applications

ABSTRACT

Q-switched and mode-locked pulse generation in Erbium-doped fiber lasers (EDFLs) are demonstrated using Poly [2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene] (MEH-PPV) organic semiconductor material as a saturable absorber (SA) for the first time. The MEH-PPV was prepared in the form of a thin film having a modulation depth of 12% and saturation intensity of 40?MW/cm². The SA was placed in a laser cavity to produce a stable Q-switched operating at 1564.0?nm. The maximum repetition rate of 78.62?kHz, minimum pulse width of 3.54?µs and maximum pulse energy of 59.45?nJ were attained at 125.2?mW pump power. On the other hand, by incorporating an additional 100?m long single mode fiber, the mode locked EDFL self-started as the pump power was raised above 125.2?mW. The soliton pulse was obtained due to the enhancement of the nonlinearity in the cavity. The mode-locked laser operated at 1568.5?nm with a fixed repetition rate of 1.859?MHz and pulse width of 2.97?ps.     

Diode-pumped Nd:YAG laser with 38 W average power and user-selectable, flat-in-time subnanosecond pulses

A diode-pumped injection-seeded Nd:YAG laser system with an average output power of 38 W is described. The laser operates at 300 Hz with pulse energies up to 130 mJ. The temporal pulse shape is nominally flat in time and the pulse width is user selectable from 350 to 600 ps. In addition, the spatial profile of the beam is near top hat with contrast <10%.     

Passively Q-Switched Diode-Pumped Continuous-Wave Nd:YAG-Cr(4+):YAG Laser with High Peak Power and High Pulse Energy

A high peak power and high pulse energy passively Q-switched diode-pumped cw Nd:YAG laser at 1.064-mum wavelength has been demonstrated with Cr(4+):YAG crystal as the saturable absorber. The average output power of 7-12 W and pulse duration of 100-250 ns was obtained with kilohertz repetition rates. The highest peak power and pulse energy obtained were 30 kW and 3.4 mJ, respectively. All the output resulted from the TEM(00) mode with M(2) < 1.1. The thermal lensing effect of the saturable absorber was investigated, demonstrating that it played an important role in optimization of the output.     

PHOTOPOLYMERIZATION AND THERMAL DECOMPOSITION OF POLYMERIZED PHASE IN C60 CRYSTALS UNDER STRONG LASER ILLUMINATION

We have investigated the photopolymerization and thermal decomposition of photochemical products with high density excitation (11–480 mW/mm²) by means of time-gated Raman scattering experiments in C₆₀ single crystal. The temperature of laser-illuminated area was measured by Stokes and anti-Stokes Raman scattering of C₆₀ Hg(1) mode, which shows the local temperature rise with increase of laser power density. The Raman intensity of Ag(2) mode rapidly decreases with irradiation time for I<170 mW/mm² indicating the rapid decrease in C₆₀ monomer density due to photopolymerization. For higher power densities, however, the Raman intensity increases after showing a minimum, which suggests a dissociation of photopolymers. The results are well explained by the rate equation model taking into account photochemical generation and thermal decomposition of photo-produced dimers. These results indicate the strong laser illumination simultaneously induces the photopolymerization and thermal decomposition.     

Semiconductor saturable absorber mirror passively Q-switched fiber laser near 2 μm

A passively Q-switched fiber laser near 2?μm is achieved with a semiconductor saturable absorber mirror (SESAM) as a saturable absorber. Stable Q-switched pulses are generated from an extremely compact setup with a central wavelength of 1958.2?nm. Under the bidirectional pump configuration, the repetition rate of the fiber laser can be widely tuned from 20 to 80?kHz by increasing the pump power at the same time the pulse width decreases from 1?μs to 490?ns. When the incident pump power is 1.3?W, the average output power, the pulse repetition rate, the pulse width, and the highest single pulse energy are 91?mW, 80?kHz, 490?ns, and 1.14?μJ, respectively. To further optimize the system configuration, the pulse width can be reduced to 362?ns when the cavity length is reduced.     

Efficient quasi-continuous-wave and passively Q-switched laser operation of a Nd3+:BaGd2(MoO4)4 cleavage plate

Pumped by a Ti:sapphire laser at 807 nm, efficient quasi-cw and passively Q-switched laser operations have been realized from a 1.1 mm thick, 1.2 at. % Nd(3+):BaGd(2)(MoO(4))(4) cleavage plate in a plano-plano cavity. When the absorbed pump power was 1060 mW, the achieved maximum quasi-cw output power was 580 mW. The slope efficiency and absorbed pump threshold power were 60% and 50 mW, respectively. Using a Cr(4+):YAG crystal with an initial transmission of 85% as the saturable absorber, a pulse laser with 3.0 microJ energy, 30 ns duration, and 52 kHz repetition rate has been obtained when the absorbed pump power was 1060 mW. The polarization characteristic and laser spectra of both the quasi-cw and passively Q-switched lasers have been measured.     

Analysis of a diode-pumped passively Q-switched Nd:GdVO4 self-stimulating Raman laser

This paper presents the theoretical and experimental results of a laser diode-pumped passively Q-switched Nd:GdVO₄ self-Raman laser in detail. In the experiment, by using two Cr⁴⁺:YAG crystals with different initial transmissions as the saturable absorber, using Nd:GdVO₄ as the gain medium and Raman medium simultaneously, the passively Q-switched operation of the Nd:GdVO₄ self-Raman laser at 1176 nm was investigated. The average power, pulse energy, pulse width and pulse repetition rate with respect to the incident pump power were measured. The obtained maximum output average power is 244.6 mW with respect to incident power of 5.7 W and the corresponding conversion efficiency is 4.3%. In the theoretical part, we used the rate equations to obtain the theoretical results. In the rate equations, the Gaussian distributions of the intracavity photon densities of the fundamental and Raman lasers and the initial population-inversion density were taken into account, and the ground-state population density of the saturable absorber at t = 0 is assumed to be uniform. The obtained theoretical results were in agreement with the experimental results on the whole.