High power fiber lasers are widely used in industrial processing such as cutting and welding. A high-power single-mode fiber laser emits laser beams in a single transverse mode (fundamental mode), exhibiting near-diffraction-limited laser transmission characteristics. It can converge into smaller light spots and achieve higher power density. Therefore, it serves as a preferred laser source for precision machining tasks involving high-speed and high-precision cutting, such as cutting of high-reflective materials, welding of dissimilar metal materials, and other industrial precision processing scenarios. It can also serve as a basic module for achieving higher laser power output with good beam quality through beam combining. The power scaling of a single fundamental mode fiber laser is limited by factors, such as transverse mode instability and nonlinear effects. This article introduces multi-stage amplified structures that employs wavelength-stabilized 976nm pump diodes, homemade fiber gratings, cladding light strippers and pump combiners. With the high-performance homemade Raman scatter suppressor and a well-designed fiber coiling approach, the high-order modes and Raman light in fiber laser are suppressed effectively. A single fundamental mode continuous laser has been achieved stably at maximum output power of 3 kW, optical slope efficiency of 79.97 %, M2 factor of 1.05, and Raman suppressed ratio of ≥ 35dB. Further improvements can be made by increasing the pump source power and enhancing the filtering efficiency of the Raman scatter suppressor, which is expected to enable higher single fundamental mode power output.
KEYWORDS: Beam combiners, Fiber lasers, Optical fibers, Fusion splicing, High power lasers, High power fiber lasers, Cladding, Power meters, Fabrication, Thermal imaging cameras
Incoherent laser beam combining based on signal combiners is an effective method to significantly increase the laser power. Although many high power signal combiners have been reported, most of these combiners have seven or less input ports. In this paper, a 19×1 signal combiner is fabricated based on tapered fiber bundle technique including optical fibers bundling with capillary, fiber bundle tapering, cutting, and fusion splicing to the output fiber. The input fibers of the combiner are 14/250 μm-core/cladding optical fibers, and the output fiber is a 100 μm-diameter-core multimode fiber. The signal combiner is tested with eight 1500 W fiber laser modules, and 11.55 kW output power is obtained. The beam parameter product is 3.83 under 2 kW laser output. The temperature rise of the signal combiner is measured under passive heat dissipation condition at different laser power outputs, and the thermal slope is calculated to be 1.56 °C/kW. This 19×1 combiner has the potential to be used in a 30kW-level or even higher power fiber laser system.
In this paper, we propose that a Chirped and Tilted Fiber Bragg Grating (CTFBG) can be fabricated in the 14um-core fiber to suppress SRS to achieve a higher-power single-mode fiber laser. The results show that the CTFBGs can suppress the SRS about 25 dB, and the power of the 14um-core single-mode fiber laser can be improved to 3 kW. The M2 of the laser is less than 1.20. The CTFBGs are fabricated with an excimer laser and the heating rate of the recoated CTFBGs are less than 0.01 °C/W. The research results have certain significance for suppressing SRS in high-power single-mode fiber lasers with CTFBG for improving the output power.
We present a type of diffractive lenses “Zernike apodized photon sieves” (ZAPS), which structure is based on the combination of two concepts: apodized photon sieves and Zernike phase-contrast. In combination with the synchrotron light sources, the ZAPS can be used as an objective for high-resolution X-ray phase-contrast microscopy in physical and life sciences. The ZAPS is a single optic that integrates the appropriate ±π/2 radians phase shift through selective zone placement shifts in an apodized photon sieve. The focusing properties of the ZAPS can be easily controlled by apodizing its pupil function. An apodized photon sieve with Gaussian pupil was fabricated by lithographic technique and showed that the side-lobes have been significantly suppressed at the expense of slightly widening the width of the main lobe.
A fiber-optic interferometer to measure differences in temperature between two single-mode fiber arms is described.
Temperature changes are observed as a motion of an optical interference fringe pattern. Values are calculated for the
temperature dependence of the fringe motion. Temperature measurements are made with the interferometer, and the
experimental results for sensitivity are in good agreement with the theoretical values.
The goal of deconvolution microscopy for phase-contrast imaging is to reassign the optical blur to its original position
and to reduce statistical noise, thus visualizing the cellular structures of living cells in three dimensions and at
subresolution scale. The major features of this technology for a phase-contrast microscopy are discussed through a series of theoretical analyses. A few of possible sources of aberrations and image degradation processes are presented. The theoretical and experimental results have shown that deconvolution microscopy can enhance resolution and contrast by either subtracting or reassigning out-of-focus blur.
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