K. Ranganathan

Simultaneous Q-switching and mode-locking in an intracavity frequency doubled diode-pumped Nd:YVO4/KTP green laser with Cr4+:YAG

We report intracavity second harmonic (at 532 nm) generation in a passively Q-switched mode-locked Nd:YVO 4 laser. The width of a typical Q-switched envelope of the mode-locked pulses for the green laser was around 65 ± 5 ns and the repetition rate for the mode-locked pulses was 400 MHz. The intracavity frequency doubling significantly improves the depth of modulation of the mode-locked pulses. The peak power of a single mode-locked green pulse near the center of the Q-switched envelope was estimated to be more than 2 kW and the average green power was 6 times higher than the CW green power at an incident diode pump power of 6 W.

An alternative approach to determine the fractional heat load in solid state laser materials: application to diode-pumped Nd:YVO4 laser

Abstract A simple approach is described and used for on-line measurement of the fractional heat-load parameter ξ in an operating diode-pumped Nd:YVO4 laser at 1.06 μm wavelength for different doping concentrations. The method is based on the fact that if the thermo-optical properties of the sample are known then the ξ-parameter can be estimated from the measured effective focal length induced by the pump beam and any other lensing effect due to mechanical mounting of the sample for a given pumping configuration. The value of the fractional heat-load parameter estimated by our technique was in excellent agreement with the earlier reported values.

Experimental determination of effective stimulated emission cross-section in a diode pumped Nd:YVO4 micro-laser at 1064 nm with various doping concentrations

Abstract A practical method is described and used for determination of the effective stimulated emission cross-section ( σ e ) in an operating diode pumped Nd:YVO 4 micro-laser at 1064 nm with various doping concentrations. In this method a micro-laser is formed by keeping a small piece of the sample in a plane–plane resonator under semi-monolithic configuration and a fiber coupled diode laser ( 808 nm ) was used for pumping. The pump power induced thermal lensing effect was used to make the cavity stable. In thermally stabilized solid-state lasers the cavity parameters change dynamically with the pump power and hence the overlap integrals become a function of the absorbed pump power. In our method the overlap integrals were estimated by measuring the thermal lens focal length at the threshold. The value of σ e of Nd:YVO 4 crystal with different doping concentrations obtained by this method were in well agreement with the reported values.

82 W Continuous-Wave Green Beam Generation by Intracavity Frequency Doubling of Diode-Side-Pumped Nd:YAG Laser

Highly efficient and high-power continuous-wave (CW) green beam generation by intracavity frequency doubling of diode side-pumped Nd:YAG laser using a water cooled high gray track resistant potassium titanyl phosphate crystal is demonstrated in a Z-shaped resonator design ensuring resonator stability over the entire range of the pump power with optimized spot sizes at the respective intracavity components configuration. A maximum of 82.5 W of CW green power was obtained at a total diode pumping power of 750 W, corresponding to 11% pump to green beam conversion efficiency. The green power increases linearly with pump power without any sign of power rolloff, and no damage of the crystal due to thermal lensing or gray tracking is observed. The long-term stability is excellent with ±0.7% variation in the output power. The short-term rms intensity fluctuation is measured to be ±0.2%. The performance of the laser by considering the pump-power-induced thermal lensing effect and the M2 parameter at the fundamental wavelength has been analyzed. The theoretical model showed excellent agreement with the experimental results.

Generation of flattened Gaussian beam profiles in a Nd:YAG laser with a Gaussian mirror resonator

We report the experimental generation of a family of flattened Gaussian beams with bell-shaped, flattened, and annular intensity profiles in an electro-optically Q-switched Nd:YAG laser with a variable reflectivity mirror of a Gaussian reflectivity profile as an output coupler. The laser beams of different profiles were generated by modifying the resonator magnification. The propagation characteristics of the experimentally generated flat Gaussian beams were found to be in agreement with theory. To the best of our knowledge this is the first time such a family of flattened Gaussian beams is experimentally generated intracavity using a single variable reflectivity mirror.

A novel technique to generate orthogonal polarizations in Q-switched solid-state lasers

Here, we report a novel technique for selective generation of either of the two orthogonally polarized beams from the same resonator cavity of an electrooptically Q-switched solid-state laser without introducing any additional optics. A theoretical analysis of the resonator set up along with realization of the technique has been demonstrated with similar output energy, pulse width, beam parameter product and transverse profile in both of the orthogonally polarized beams.

Application of Meshes to Extract the Fabricated Objects in Selective Laser Melting

A new, yet a very simple solution to extract the job fabricated by selective laser melting (SLM) technique are reported here. Usually when objects were fabricated using metal powder, the substrate/base plate made of same metal is used in order to achieve better bonding. Jobs fabricated on such substrates need machining to extract it from the substrate. It is proposed to fabricate the job over a wire mesh fixed above the metallic substrate to facilitate the easy removal of the finished job from the substrate. In this paper we have used stainless steel powder to grow objects on stainless steel wire mesh using SLM. It is also shown that mesh is a better choice when compared with stainless steel foil. Mesh along with the job can be detached from the base plate by cutting the binding wires. Role of base plate is to give solid support and the role of mesh is to provide support as well as to facilitate the easy extraction of fabricated objects. This particular technique could be very useful in the cases of fabricating thin walled delicate jobs and porous jobs.

Modular pump geometry for diode side-pumped high-power Nd:YAG rod laser.

In this paper, we present a modular design configuration to side-pump an Nd:YAG rod of a diode-pumped high-power CW laser. Independent modules in the form of discs are loaded with three-diode linear bar arrays at 120° with respect to each other and are assembled along the length of the rod. By keeping successive discs at three different angular separations (the minimum, intermediate, and maximum), helical, 60° rotated, and linear geometries, respectively, were created. Parameters like thermal lensing, fluorescence profile, laser beam profile, and beam quality factor (M2) were studied to compare the performances of different geometries. The results indicate that the 60° rotated configuration provides the best performance when compared with rest of the schemes. To the best of our knowledge, this is the first time that such novel modular-type pump geometries with a provision for the angular separation of pump diodes have been tried.

Modular pump head design of diffused, metal, and hybrid pump geometry for diode-side-pumped high power Nd:YAG laser

In this paper, we present a comparative study on pump heads for a high power diode-side-pumped Nd:YAG laser. The pump head is a modular type, which is in the form of discs, with each disc holding three pump diodes kept at 120° with respect to each other. Unabsorbed pump light from the active medium is reflected by reflectors mounted adjacent to the pump diodes. The performance of a high power pump head made of modular discs mounted with specular or diffused type reflectors was studied. Hybrid pump geometry was also investigated, where the pump head is made up of discs loaded with metal and diffused reflectors, alternately. The discs are loaded around the active medium in such a way that successive discs are rotated by sixty degrees with respect to each other. Fluorescence profiles, thermal lensing, laser output power, and M2 values were studied for pump heads made up of metal, diffused, and hybrid type reflectors. All of the pump heads were studied for three different resonator lengths to maximize the output power with the best beam quality. The experimental results show that the diffused reflector-based geometry in a sixty degree rotated configuration produced the maximum output power and best beam quality in terms of the M2 value.