Laser-diode-pumped Nd:YAG active-mirror laser

We describe a simple design, laser-diode-pumped cw Nd:YAG active-mirror laser and present a thermal analysis of the crystal. A cw output power of 2.4 W and an M(2) beam quality value of less than 1.9 at an incident pumping power of 8.9 W were obtained. From the thermal analysis we predict that the output power can be increased by increasing the pump beam diameter and the pump power at a constant excitation density.     

Frequency stabilization of a single-frequency Q-switched Tm:YAG laser by using injection seeding technique

A stable single-frequency Q-switched Tm:YAG laser was demonstrated. The laser was injection seeded by a monolithic nonplanar ring oscillator laser utilizing the ramp-hold-fire technique. The measurements of the output parameters were presented. This paper focused on investigation of the frequency stability of the injection-seeded laser, which was measured by optical heterodyne technique. A method used to restrict the frequency jitter of the laser was discussed. The fluctuation of the laser frequency was reduced from 2.36 MHz (rms) to 1.07 MHz (rms) in 1 h by optimizing the voltage of the piezoelectric translator.     

Segment side-pumped Q-switched Nd:YAG laser

In the design of conduction-cooled lasers, a side-pumped configuration is an attempt to solve the space conflict between pump and heat removal. The pump radiation always competes with the heat removal and mechanical support device for the lateral surface of a laser rod. This space conflict can be addressed by a segment side-pumped configuration in which circular laser diode arrays and heat-conducting rod holders alternate periodically along the length of the laser rod. This scheme permitted 11 Hz operation of a 190 mJ Q-switched laser at the wavelength of 1064 nm without the use of liquid cooling for both the laser rod and laser diode arrays and the corresponding optical-optical conversion efficiency of 23.1%. Thus, it has great potential to be used in compact and miniature laser systems.     

Doubly Q-switched tape casting YAG/Nd:YAG/YAG ceramic laser

A doubly Q-switched 1.06 μm pulsed laser using a novel tape casting YAG/Nd:YAG/YAG composite ceramic with a sandwich structure was demonstrated for the first time. Compared to purely acousto-optical (AO) Q-switching, this laser using an AO Q-switch and Cr⁴⁺:YAG saturable absorber simultaneously can generate shorter pulses. The pulsed laser performance was investigated at two modulated repetition rates of 10 and 20 kHz.     

Diode-pumped 100-W green Nd:YAG rod laser

We developed a diode-pumped high-average-power Nd:YAG green laser. By use of a monolithic diffusive reflector having three slits and a rod with low doping concentration, uniform distribution of excited Nd ions could be achieved. Uniform distribution in the rod reduced thermal birefringence. We employed a Z-shaped cavity to have a constant beam size at the frequency-doubling crystal independent of thermal lensing in the rod. The pulse width and green power dependence on the pump power were analyzed. A maximum green power of 101 W was obtained when the total pump power was 398 W. The optical-to-optical conversion efficiency was as high as 25.4%.     

Compact scalable diode-pumped Nd:YAG ceramic slab laser

We describe our preliminary studies of the use of neodymium-doped slab-shaped ceramic YAG media in the construction of compact, rugged, high-power diode-pumped solid-state lasers. A maximum extraction of more than 160 W at a 20% slope efficiency level, with a narrow transverse direction beam-parameter product of the order of 4 mm mrad(-1) is experimentally obtained from an extremely simple and compact (overall dimensions 160 mm x 100 mm x 60 mm) laser head in a quasi-continuous-wave regime. Experimental data together with finite-elements method simulations indicate that power extraction can be scaled up at least to 900 W cw with this laser head geometry.     

Rough surface absorption of Nd:YAG laser rods

The rough surface of Nd:YAG-laser rods exhibits a broad spectral absorption due to impurities. The optical density of the investigated surfaces was determined up to several percent in the near infrared and visible spectral range. The characteristics of the rough surface absorption was investigated.     

Characterization of plasma propulsion by Nd:YAG laser

Significant propulsion parameters, specific impulse and coupling coefficient for the different metallic pendulums are presented. 4 N (99.99%) pure, solid targets are in the form of foils of aluminium, copper and gold. The targets are irradiated by Q-switched pulsed Nd:YAG laser (1064 nm, 10 mJ, 1.1 MW, 9-14 ns) under standard conditions of temperature and pressure. Plasma plume of these targets is also observed by employing CCD (BOSCH LTC0510, monochrome camera) based, computer controlled image capturing system and it was seen that expansion of plasma plume for oscillating targets is anisotropic in air. The results reveal that not only very high exhaust velocity of propellant 10⁶ m/s is achieved but also very specific impulse values of Al, Cu and Au targets (3.14 × 10⁶ s, 1.37 × 10⁷ s, 7.16 × 10⁵ s respectively) are obtained. Coupling coefficients are for Al, Cu and Au were 1.54 × 10³ (N-s/J), 1.88 × 10³ (N-s/J), and 1.08 × 10³ (N-s/J) respectively.     

Investigation of the misalignment sensitivity of a birefringence-compensated two-rod Nd:YAG laser system

A system for the compensation of thermally induced birefringence in laser rods that consists of two identical Nd:YAG laser rods, a telescope to image the principal planes of the rods onto each other and a 90 degrees quartz rotator to change the state of polarization between the rods has been set up, and its sensitivity to transversal and longitudinal misalignment has been investigated experimentally. A theoretical model to describe the increase of depolarization that is due to misalignment has been developed and compared with the experimental results.     

Diode-pumped 214.8-nm Nd:YAG /Cr4+:YAG microchip laser system for the detection of NO

A passively Q-switched 214.8-nm Nd:YAG/Cr(4+):YAG microchip laser system for the detection of NO was designed, constructed, and tested. The system uses the fifth harmonic of the 1.074-microm transition in Nd:YAG to detect NO by laser-induced fluorescence. A significant challenge was the development of an environmentally stable coating to provide the necessary discrimination between the 1.074-microm laser line and the stronger transition at 1.064 microm. The exact position of the fifth-harmonic frequency was determined by use of NO fluorescence excitation spectra to be 46556 +/- 1.5 cm(-1). With a pulse energy of approximately 50 nJ of fifth-harmonic light, we observed a detection sensitivity for NO of approximately 15 parts per billion by volume in a simple, compact optical system.     

Cracking in Be/Al Nd: YAG laser weld

An investigation was conducted to determine the cause of weld cracking in laser Be/Al weldments. In agreement with earlier studies, features consistent with hot shortness cracking on the fracture surfaces were observed. Closer examinations of the fusion zone crack regions reveal that the cracking was a result of thermal stress, shape of weld roots and impurities segregation. The defects are related to the weld parameters. The cracks easily nucleate at conduction mode weld and blowholes easily appear at keyhole mode weld.     

Design of a high-power Nd:YAG Q-switched laser cavity

An electro-optically Q-switched Nd:YAG laser resonator that uses two end prisms placed orthogonally perpendicular to each other has been designed. This configuration improves the stability of the resonator and does not alter the characteristics of the electro-optical Q switch. The outcoupling ratio of the cavity is optimized by a change in the azimuthal angle of a phase-matched Porro prism placed at one end of the cavity. The prism placed at the other end of the cavity is designed so that it introduces a phase change of II, regardless of its orientation and index of refraction, resulting in a more efficient and stable cavity.     

Amorphous carbon-silicon heterojunctions by pulsed Nd:YAG laser deposition

Amorphous carbon (a-C) films were deposited at 10^− 4 Pa on n-Si (Si-111) and p-Si (Si-100) substrates using a pulsed Nd:YAG laser with fundamental, second- and third-harmonic outputs. These unhydrogenated and undoped a-C films were characterized by visible and UV Raman spectroscopy which indicated the presence of substantial amount of sp³ hybridized carbon network depending on the laser wavelength. The bulk resistivity in the Au/a-C/indium tin oxide structure varied between (10⁹-10¹³) Ω cm — the lowest resistivity was obtained for films deposited by the fundamental laser output at 1064 nm while the highest value was by the third-harmonic laser output at 355 nm. All the a-C/Si heterostructures exhibited a nonlinear current density-voltage characteristic. Under light illumination, by taking into consideration the fill factor of ~ 0.2 for a-C/n-Si, the conversion efficiency at the highest photovoltage and photocurrent, at an illumination density of 0.175 mW/cm² was estimated to be ~ 0.28%.     

Passive Q switching of a solar-pumped Nd:YAG laser

Passive Q switching is a preferable choice for switching the Q factor of a solar-pumped laser because it requires neither a driver nor an electrical power supply. The superior thermal characteristics and durability of Cr(4+):YAG single crystals as passive Q switches for lamp and diode-pumped high-power lasers has been demonstrated. Here we report on an average power of 37 W and a switching efficiency of 80% obtained by use of a solar-pumped Nd:YAG laser Q switched by a Cr(4+):YAG saturable absorber. Concentration of the pumping solar energy on the laser crystal was obtained with a three-stage concentrator, composed of 12 heliostats, a three-dimensional compound parabolic concentrator (CPC) and a two-dimensional CPC. The water-cooled passive Q switch also served as the laser rear mirror. Repetition rates of as much as 50 kHz, at pulse durations between 190 and 310 ns (FWHM) were achieved. From the experimental results, the saturated single-pass power absorption of the Cr(4+):YAG device was estimated as 3 ? 1%.     

Time-resolved measurements of statistics for a Nd:YAG laser

Time-resolved measurements of the fluctuating intensity of a multimode frequency-doubled Nd:YAG laser have been performed. For various operating conditions the enhancement factors in nonlinear optical processes that use a fluctuating instead of a single-mode laser have been determined up to the sixth order. In the case of reduced flash-lamp excitation and a switched-off laser amplifier, the intensity fluctuations agree with the normalized Gaussian model for the fluctuations of the fundamental frequency, whereas strong deviations are found under usual operating conditions. The frequencydoubled light has in the latter case enhancement factors not so far from values of Gaussian statistics.     

All-solid-state tunable DCM dye laser pumped by a diode-pumped Nd:YAG laser

Lasing is observed near 620 nm in a DCM dye doped TiO(2)-content organically modified silicate (ORMOSIL) pumped by frequency-doubled radiation from a diode-pumped Q-switched Nd:YAG laser. The laser wavelength is tunable over 60 nm. A conversion efficiency of 18% is obtained at its central wavelength of 621 nm. The laser output energy has only a 10% reduction after 27,000 pulses at a pump repetition rate of 30 Hz and a pump intensity of 1 J/cm(2). An all-solid-state, compact, long-lifetime, and tunable dye laser has been demonstrated.     

Miniaturized, high-power diode-pumped, Q-switched Nd:YAG laser oscillator-amplifier

A miniaturized, passively Q-switched Nd:YAG laser oscillator-power amplifier is reported, which is axially pumped by a compact, fiber-coupled, high-power, quasi-cw diode laser module. The pumping intensity of the oscillator crystal can be adjusted independently of the pumping intensity of the amplifier. This ensures that the oscillator pulse enters the amplifier when its maximum population density is reached. Furthermore, pulse bursts can be generated with a definite, adjustable number of single pulses. Maximum pulse energies of 8.4?and 22?mJ were achieved for a single pulse and for a pulse burst, respectively, at a pumping power of 470?W. The pulse widths were 2?ns, whereas the beam quality corresponded to M2<1.5. The laser is appropriate for scaling the power to the 10?MW range. Operation by using a 100?m pumping fiber was demonstrated.     

Localized boriding of low-carbon steel using a Nd:YAG laser

Localized boriding of low-carbon steel by the conventional technique requires tedious preboriding treatment and a long processing time. Laser boriding of low-carbon steel can be performed faster, and without any preboriding treatment. The feasibility of selective boriding of AISI 1018 steel using a NdYAG laser has been investigated. High hardness in the range 950–2200 H_v was obtained during laser boriding of AISI 1018 steel. The wide range of hardness is due to the variety of microstructures possible during laser boriding. Electron microprobe analysis showed that the highest hardness (2200 H_v) was due to the formation of FeB, and the lowest hardness was due to a mixture of Fe₂B and eutectic (_Fe+Fe₂B). The most desirable microstructure in laser boriding of AISI 1018 steel was found to be Fe₂B, which incorporates a combination of a high hardness, in the range of 1300–1700 H_v, and a compressive stress at the treated surface.