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The hole-coupling method, which is commonly used in the optically pumped THz gas laser, will reduce the beam quality due to the hard-edge diffraction. It is shown that by optimizing the parameters of the resonator a diffraction-limited output beam can be obtained. A method is proposed for the selection of a higher order waveguide mode, whose first zero point along the radial direction coincides with the edge of the output hole coupler and the effect of hard edge diffraction is depressed. Measurements of beam quality are taken on an experimental prototype whose optical setup is designed by this method. A quasi-Gaussian beam output is obtained, and the beam quality M² factor is about 1.15. [ABSTRACT FROM AUTHOR]

In spectral beam combining systems, the locked spectra of the diode laser array are determined by the interaction between the internal cavity and the external cavity. Using the multibeam interference theory, spectral modes locked by the coupled cavity are numerically calculated and analyzed. A spectral mode of a diode emitter is divided into a main lobe, a left sidelobe, and a right sidelobe, which is mainly affected by the position of the diode emitter. Based on the locked spectral modes, a beam propagation model in the grating-external cavity is established by the diffraction integral method and the incoherent superposition principle. The effects of the interval between two adjacent emitters, the reflectivity of the front surface, and the distance between the grating and the coupler on the characteristics of the combined beam have been discussed in detail. The results show that the beam quality and the spot size of the combined beam gradually degrade with the increasing interval. By reducing the reflectivity of the front surface of the diode emitter and decreasing the distance between the grating and the coupler, the beam quality can be improved. Among the three factors, such as the interval between two adjacent emitters, the reflectivity of the front surface of an emitter, and the diffraction distance, the interval has the most sensitive impact on the combined beam characteristics. Thus a beam shrinker to convert big beams into small beams in diameter can be adopted to optimize the combined beam. [ABSTRACT FROM AUTHOR]

Laser transmission welding (LTW) of thermoplastics is a direct bonding technique already used in different industrial applications sectors such as automobiles, microfluidics, electronics, and biomedicine. LTW evolves localized heating at the interface of two pieces of plastic to be joined. One of the plastic pieces needs to be optically transparent to the laser radiation whereas the other part has to be absorbent, being that the radiation produced by high power diode lasers is a good alternative for this process. As consequence, a tailored laser system has been designed and developed to obtain high quality weld seams with weld widths between 0.7 and 1.4 mm. The developed laser system consists of two diode laser bars (50 W per bar) coupled into an optical fiber using a nonimaging solution: equalization of the beam parameter product (BPP) in the slow and fast axes by a pair of step-mirrors. The power scaling was carried out by means of a multiplexing polarization technique. The analysis of energy balance and beam quality was performed considering ray tracing simulation (ZEMAX®) and experimental validation. The welding experiments were conducted on acrylonitrile/butadiene/styrene (ABS), a thermoplastic frequently used in automotive, electronics and aircraft applications, doped with two different concentrations of carbon nanotubes (0.01% and 0.05% CNTs). Quality of the weld seams on ABS was analyzed in terms of the process parameters (welding speed, laser power and clamping pressure) by visual and optical microscope inspections. Mechanical properties of weld seams were analyzed by mechanical shear tests. High quality weld seams were produced in ABS, revealing the potential of the laser developed in this work for a wide range of plastic welding applications. [ABSTRACT FROM AUTHOR]

We numerically calculated and analyzed the influence of a 7 × 1 fiber power combiner on supercontinuum (SC) laser beam quality in the range of 0.5 to 2.3 μm. The calculation results show the M2 oscillates within a range for a specific wavelength as the length of the output fiber changes. When the length of the output fiber is fixed, whether single input fiber or all fibers are injected with SC lasers, the M2 of the SC shows a nonlinear change and oscillates continuously throughout the entire spectrum, while it first decreases and then increases as the wavelength increases as a whole. Analysis of the numerical results shows that by changing the type of input fiber and the taper waist structure, the beam quality of both long-band and short-band parts of the SC laser can be improved. To verify theoretical calculations, the divergence angle of SC was measured as the beam quality after being transmitted by one 7 × 1 fiber power combiner in the spectral range from 0.5 to 2.3 μm. The divergence angle first decreases but then increases with a prolonging wavelength, and the curve of the experimental result renders a basic match with the calculation. To the best of our knowledge, currently no overall evaluation is reported on the beam quality of combined SC sources. [ABSTRACT FROM AUTHOR]

We demonstrate the performance of a 968-nm laser-diode (LD) side-pumped Er,Pr:YAP laser in free-running and electro-optical (EO) Q-switched modes with emission at 2.7 μm, respectively. In the free-running mode, a maximum power of 11 W is achieved at a working frequency of 150 Hz and a pulse width of 200 μs, corresponding to the single pulse output energy of 73.3 mJ and slope efficiency of 13.3%. In the EO Q-switching mode, a giant pulse laser is obtained with pulse energy of 20.5 mJ, pulse width of 61.4 ns, and peak power of 0.33 MW at the highest working frequency of 150 Hz, corresponding to the energy extraction efficiency of 71.4%. In addition, dual-wavelength laser at 2713 and 2732 nm and beam quality factors Mx2/My2 of 6.62/6.66 are measured, respectively. The results indicate that a 2.7-μm laser with a high repetition rate and high peak power can be realized through LD side-pumped and EO Q-switched Er,Pr:YAP crystal. [ABSTRACT FROM AUTHOR]

Currently, the highest power quantum cascade lasers (QCLs) include (i) an efficient active region design, which minimizes the energy fraction transferred into heat, (ii) a relatively large number (40) of cascades, which increases the mode confinement factor, Γ, and (iii) narrow buried-heterostructure waveguides, which efficiently cool the active region through efficient lateral heat flow. This combination allows watt-level continuous wave (cw) emission powers at room temperature. Moreover, narrow waveguides favor the fundamental TM00 lateral mode, resulting in a nearly Gaussian beam. To the extent that power efficiency is already largely optimized, power scaling in narrow-stripe QCLs is only possible through increasing the laser length, which is limited by the needs for robust construction and transparent antireflection coatings. Broad-area (BA) QCLs with a small number of cascades can also deliver watt-level cw powers at room temperature, profiting from the enhanced vertical heat flow. Power can be scaled for these lasers also via the laser width and is nearly unlimited. The usual drawback of the BA lasers is poor beam quality. We discuss the use of tapered QCLs and the first demonstration of room temperature cw operation of the BA QCL in fundamental TM00 mode. A stable and reproducible transverse optical mode is achieved using a double-taper waveguide geometry. The laser emits at 4.6 μm and has a demonstrated room temperature cw power of 100 mW. [ABSTRACT FROM AUTHOR]

Compared to zig-zag solid-state slab lasers, zig-zag solid-state tube lasers (SSZTLs) exhibit significant potential in beam quality improvement and output power enhancement. However, the progress of SSZTLs still faces enormous challenges due to the lack of effective control of beam quality. We first developed a comprehensive model for analyzing the output beam quality of zig-zag tube lasers by taking both the fabrication and alignment errors and thermal effects into consideration. The primary factors degrading the beam quality and thermal stability of the SSZTLs were analyzed in detail, and a self-correction method based on the complementary optical path was further proposed and analyzed theoretically to effectively improve the beam quality and thermal stability of the SSZTLs. The results show that this method can not only effectively correct the off-axis aberrations but also mitigate the depolarization loss that arises from the thermal instability of the SSZTLs. This work can provide a reference in the beam control and applications of SSZTLs. [ABSTRACT FROM AUTHOR]

Extending existing scalar Schell-model source work, we derive the M2 factor for a general electromagnetic or vector Schell-model source to assess beam quality. In particular, we compute the M2 factors for two vector Schell-model sources found in the literature. We then describe how to synthesize vector Schell-model beams in terms of specified, desired M2 and present Monte Carlo simulation results to validate our analysis. [ABSTRACT FROM AUTHOR]