Compact High-power Laser Research Articles

Energy transfer mechanisms and non-radiative losses in Nd3+ doped phosphate laser glass: Dopant concentration effect study

The aim of the present work is to show a simple quantitative theoretical study on the relaxation mechanisms of the 4F3/2 levels of the Nd3+ ions in the widely used meta-phosphate laser glass system (P2O5–Al2O3–BaO–K2O) for the studied concentration range of the Nd3+ ions from 0.10 × 1020 to 8.15 × 1020 ions/cm3. Auzel's diffusion-limited model for energy transfer has been adopted in the present study for estimating zero concentration level lifetime, τ0 of 4F3/2 levels in the Nd3+ ions present in the studied glass matrix. Primarily, the relaxation mechanisms are dominated by radiative decay (krad) and energy transfer to hydroxyl groups (kOH) present in the glass network structure up to the dopant, Nd3+ concentration 0.78 × 1020 ions/cm3. Later on, with increasing dopant ion concentration, fluorescence from trivalent Nd3+ ions is unfortunately quenched by the interaction between Nd3+ ions, also known as concentration quenching. The concentration quenching of the fluorescence lifetime has been analysed using proposed Inokuti-Hirayama (I–H), Yokota-Tanimoto (Y-T) and Brushtein (B) models and found to be migration-assisted cross-relaxation mechanisms at or beyond 1.47 × 1020 ions/cm3 dopant concentration. The diffusion coefficient, D derived from the Y-T model and the energy migration rate, Wm attained from the B model has demonstrated diffusion-based energy migration initially at about >1.47 × 1020 ions/cm3 Nd3+ concentration and after that, it has switched to a hopping mechanism with further increasing ion concentration, >2.97 × 1020 ions/cm3. Critical quenching concentration, Q and critical radius, R0 for the studied glass composition have also been determined and correlated to the experimental results. No evidence for ion clustering has been found within the studied dopant ion concentration range (0.10 × 1020 - 8.15 × 1020) ions/cm3 with respect to the estimated R0. Finally, the contribution of the individual relaxation process to the experimentally recorded emission spectra and measured lifetime, τexp has been investigated in order to identify the most suitable Nd3+ ion concentration for developing large-aperture high-energy/high-peak-power lasers and optical amplifiers. Therefore, the present work is expected to be significant in aiding to formulate an effective glass composition for construction of compact high-power lasers and optical amplifiers.

A Large Mode Area Parabolic-Profile Core Fiber with Modified Segmented in Cladding

In this paper, a novel fiber with a parabolic-profile core and eight segmented trenches in cladding is designed. The designed fiber consists of the segmented trench of low refractive index in cladding and parabolic-profile of high refractive index in the core. The proposed fiber has good bending resistance. The eight segmented trenches in the cladding can decrease the refractive index of cladding to increase the difference index between the core and cladding to limit fundamental mode (FM) loss. The proposed fiber can offer an effective single mode (SM) operation with a large mode area (LMA) of 952 µm2 at the small bending radius (R = 10 cm). In addition, the fiber is also suitable under an 18 W/m heat load. The proposed fiber achieves good bending performance, which can be suitable for the compact high-power lasers.

Large Mode Area Solid-Core Photonic Bandgap Yb-Doped Fiber With Hetero-Structured Cladding for Compact High-Power Laser Systems

We report on the design, realization and testing in pulsed amplification regime of a double-cladding, large mode area, polarization maintaining, solid core photonic bandgap fiber with Yb-doped core obtained from a Sol-Gel -made material. A specific hetero-structuration of the cladding has been applied to efficiently reject the higher-order modes, making the fiber single-mode in practice. When used as the last stage of a high power fiber amplifier, more than 90 W average power has been extracted at 1.03 μm wavelength with a slope efficiency of 75 % with respect to the absorbed pump power. These performances were obtained for a 6 m-long piece of fiber bent on a radius smaller than 12.5 cm. A mode field diameter of 35 μm is reported for the amplified beam with very good spatial quality and polarization extinction ratio.

Application of a compact diode pumped solid-state laser source for quantitative laser-induced breakdown spectroscopy analysis of steel

Laser-induced breakdown spectroscopy (LIBS) technology holds the potential for onsite real-time measurements of steel products. However, for a mobile and robust LIBS measurement system, an adequate small and ruggedized laser source is a key requirement. In this contribution, we present tests with our compact high-power laser source, which, initially, was developed for ignition applications. The CTR HiPoLas® laser is a robust diode pumped solid-state laser with a passive Q-switch with dimensions of less than 10 cm3. The laser generates 2.5-ns pulses with 30 mJ at a maximum continuous repetition rate of about 30 Hz. Feasibility of LIBS experiments with the laser source was experimentally verified with steel samples. The results show that the laser with its current optical output parameters is very well-suited for LIBS measurements. We believe that the miniaturized laser presented here will enable very compact and robust portable high-performance LIBS systems.

An optimized configuration of large mode field area PMMA photonic crystal fiber with low bending loss: a new approach

We propose to design a ytterbium doped two large MFA fiber for high peak power fiber laser and beam delivery application. These fiber has large MFA of 2492 µm2 when kept straight and 1021 µm2 bent over 8 cm radius at a wavelength of 1550 nm. The difference between propagation loss levels of FM and HOMs extend to efficient single mode guidance in the fiber core while bent. This allows further the fiber to make compact high power laser systems. Moreover the optimizing effective MFA of straight and bend fiber can be obtained by a suitable shape of fiber core, missing air holes in the core and the bending orientation which ultimately leads to the guidance a very high optical power. In fact the bend loss on FM and HOM of straight and bend fiber can be estimated by implementing 2D FDTD technique and it is found that, FM bend loss is very small in the order of 10−2 dB/m with bend orientation and the order of 10−3 dB/m with bend radius.

Extremely large-mode-area photonic crystal fibre with low bending loss

We report on the design of a novel flexible very large mode area photonic crystal fibre for short pulse high peak power fibre laser and beam delivery applications. This fibre has an extremely large mode area exceeding 2500 microm(2) when kept straight and over 1000 microm(2) when bent over a 10 cm radius at a wavelength of 1064 nm. In addition our fibre exhibits very small fundamental mode bending loss below 10(-2) dB/m. The large difference between the propagation loss levels of fundamental and higher order modes forces efficient single-mode guidance in the fibre core while bent. This allows using the fibre to build compact high power laser systems. The paper further explores the major features of this fibre including: the dependence of the mode field area on the fibre core shape, the influence of the bending radius and of the bending direction as well as the impact of manufacturing tolerances on the fibre specifications.

Semiconductor laser based, injection locking maintaining broad linewidth generated by a direct current modulation of a master laser

Semiconductor laser based, injection locking was performed for efficient excitation of subjects. The linewidth of the master laser was extended to 380MHz by using a frequency modulation technique through a direct current modulation. By the injection locking technique with a broad-area semiconductor laser, the frequency modulated input was amplified to 610mW, faithfully maintaining the broadened linewidth and the spectral shape. This result means that a compact high power laser system is possible with broad linewidth that is precisely controllable.

Design approaches for laser-diode material-processing systems using fibers and micro-optics

Low-cost, efficient, and compact high-power laser diodes (LDs) will make desktop laser manufacturing (rapid prototyping, sintering, drilling, marking, etc.) a reality soon. Laser processing of materials requires not only high average power, from tens of watts to kilowatts, but also high incident beam intensity or power density, from 103 to 108 W/cm2. Current commercial high-power LDs do emit 108 W/cm2; however, they are microscopic in size, and an individual diode emits ~ 1 W (cw) in a highly divergent (~30 x 10 deg) multimode structure. Gathering high power from a large number of such microscopic incoherent diodes into a small spot of high intensity requires micro-optic component and complex system design. Several difterent design approaches for high-intensity laser-diode systems are presented. Some of these are commercial, others will be soon, and still others will need technological developments. Possible applications and some preliminary results of direct diode-laser sintering and transformation hardening of stainless-steel ribbons are also presented.