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There has been a growing demand of laser welding for copper materials to manufacture industrial products with high electrical and thermal conductivities. The high thermal conductivity characteristic generates rapid thermal diffusion at a welding spot and hence reduces the power efficiency of laser welding. To overcome this issue, we propose to combine a blue laser beam performing a high absorptivity for copper materials, with a 1070-nm high power laser beam, launched from a single mode fiber laser. The blue laser beam can be focused at the welding spot with a sufficiently narrow beam waist, and the absorption of the blue light for copper materials is much higher than that of infrared light. Therefore, the focused blue laser beam causes rapid and highly efficient heat generation at the welding spot, and this localized heat is expected to improve the quality of laser welding. To generate the high-power blue laser beam efficiently, we fabricated a high power blue LD-integrated SLP which achieves an optical output power of 11.7 W at 10.5 A. We also fabricated a blue-DDL module using multiple SLPs and a stepped structure package adopted with a water-cooling system. The blue- DDL module can output a high fiber-coupled optical power exceeding 150 W. Next, we built a blue-NIR hybrid laser equipment which exhibits the excellent quality of laser welding by accurately controlled optical output power and beam spot diameters of both blue and NIR laser beams. In this paper, we describe the design and performance of blue LDintegrated SLP and blue-DDL module. We also report how the blue-NIR hybrid laser equipment contributes to improve the quality of the laser welding.

We have fabricated a fiber coupled semiconductor laser diode module by means of spatial beam combining of single emitter broad area semiconductor laser diode chips in the 9xx nm band. In the spatial beam multiplexing method, the numerical aperture of the output light from the optical fiber increases by increasing the number of laser diodes coupled into the fiber. To reduce it, we have tried the approach to improving assembly process technology. As a result, we could fabricate laser diode modules having a light output power of 120W or more and 95% power within NA of 0.15 or less from a single optical fiber with 125-μm cladding diameter. Furthermore, we have obtained that the laser diode module maintaining high coupling efficiency can be realized even around the fill factor of 0.95. This has been achieved by improving the optical alignment method regarding the fast axis stack pitch of the laser diodes in the laser diode module. Therefore, without using techniques such as polarization combining and wavelength combining, high output power was realized while keeping small numerical aperture. This contributes to a reduction in unit price per light output power of the pumping laser diode module.

A method based on double imaging is proposed for three-dimensional focus manipulation. A thin birefringent plate placed behind a focusing lens was applied to generate two foci with a separation smaller than the original DOF. Depth of focus enlargement of 227% was achieved without serious degradation in lateral resolution. Experimental results obtained by using a confocal arrangement were in good agreement with theory. Both theoretical considerations and experimental results showed that in non-paraxial case the ordinary and extraordinary foci could not be excited independently.

Focus duplication based on birefringence is studied with a ray tracing program with special regard to separation efficiency and aberrations. It was shown that ordinary and extraordinary foci cannot be independently generated by linearly polarized incoming beams, when the numerical aperture exceeds the 0.1 limit. Point-spread-function analysis proved that optical aberrations—especially astigmatism—represent the main limitation of high quality focus duplication.

An ytterbium based all fiber, all normal dispersion fiber oscillator with integrated SESAM can have several operation modes like mode-locked, Q-switched and noise-like. To know and to control the quality of the mode-locking is essential for the application of such laser oscillators, otherwise the whole laser setup can be damaged or the expected operation characteristics of the oscillator driven systems cannot be achieved. Usually the two-photon signal generated by the short pulses is used to indicate the mode locked operation, however such detection can be misleading in certain cases and not always able to predict the forthcoming degradation or vanishing of mode locking. The characterization method that we propose uses only the radio frequency spectrum of the oscillator output and can identify the different operation regimes of our laser setup. The optical spectra measured simultaneously with the RF signals proves the reliability of our method. With this kind of characterization stable mode locking can be initiated and maintained during the laser operation. The method combined with the ability to align the polarization states automatically in the laser cavity leads to the possibility to record a polarization map where the stability domains can be identified and classified. With such map the region where the mode locking is self starting and maintainable with minimal polarization alignment can be selected. The developed oscillator reported here with its compact setup and self alignment ability can be a reliable source with long term error free operation without the need of expensive monitoring tools.

A line-scanning tomographic optical microscope system requires precise rotation of the scanning line. Center of rotation error introduced by both the imprecision of optical and mechanical components is studied experimentally and via simulations. It was shown that a practical tolerance limit can be chosen where the influence of the investigated error on the reconstructed image quality remains insignificant. An effective and simply practical solution was presented to keep the center of rotation error below this tolerance limit and the spatial resolution of the reconstructed image close to the diffraction limit.

Line-scanning tomographic optical microscopy (LSTOM) requires precise rotation of the scanning line. We demonstrate a method that applies translation-invariant optical elements (polarizer and birefringent plate) to minimize the rotation error. An astigmatic line produced by means of a focused beam through a birefringent plate is used as line illumination. A comparative theoretical and experimental study is presented using an LSTOM system.

An imaging method and optical system, referred to as a line-scanning tomographic optical microscope (LSTOM) using a combination of line-scanning technique and CT reconstruction principle, is proposed and studied theoretically and experimentally. In our implementation a narrow focus line is scanned over the sample and the reflected light is measured in a confocal arrangement. One such scan is equivalent to a transverse projection in tomography. Repeating the scanning procedure in several directions, a number of transverse projections are recorded from which the image can be obtained using conventional CT reconstruction algorithms. The resolution of the image is independent of the spatial dimensions and structure of the applied detector; furthermore, the transfer function of the system is isotropic. The imaging performance of the implemented confocal LSTOM was compared with a point-scanning confocal microscope, based on recorded images. These images demonstrate that the resolution of the confocal LSTOM exceeds (by 15%) the resolution limit of a point-scanning confocal microscope.

In this paper an optical system is proposed to generate radially and azimuthally polarized beams. A focused monochromatic beam is divided into ordinary and extraordinary parts by using a thin plane parallel uniaxial crystal plate. If the optical axis of the crystal is perpendicular to its surface, the two generated foci can be associated with azimuthal and radial polarization states, respectively. The generated foci were studied theoretically and experimentally using a focusing objective with a moderate numerical aperture (NA = 0.45) and different kinds of uniaxial crystal.