A diode-pumped actively Q-switched and actively mode-locked Tm3+-doped double-clad silicate fiber laser is reported providing up to 5 W of average output power at ~60 kHz Q-switch envelope repetition rate and ~8 μJ subpulses with up to 2.4 kW peak power. Using this source as a pump laser for supercontinuum generation in a ZBLAN fiber, over 1080 mW of supercontinuum from 1.9 μm to beyond 3.6 μm was obtained at an overall efficiency of 3.3% with respect to the diode pump power.
We demonstrate a three-stage diode-pumped Yb:YAG single-crystal-fiber amplifier to generate femtosecond pulses at high average powers with linear or cylindrical (i.e., radial or azimuthal) polarization. At a repetition rate of 20 MHz, 750-fs pulses were obtained at an average power of 85 W in cylindrical polarization and at 100 W in linear polarization. The report includes investigations on the use of Yb:YAG single-crystal fibers with different length/doping ratio and the zero-phonon pumping at a wavelength of 969 nm in order to optimize the performance.
sharply focus such a beam [1] makes it a versatile tool for various applications [2] such as plasmon excitation, optical trapping and laser material processing. In the field of cutting thick metal sheets with a radially polarized laser the benefits were outlined theoretically in 1999 by Niziev et al. [3]. In 2007 it was demonstrated by Meier et al. that the drilling speed of holes in mild steel with a Q-switched nanosecond laser can be increased by a factor of 1.5-4 by using azimuthally polarized laser radiation instead of linear or circular polarization [4]. Furthermore, it was experimentally shown that picosecond lasers with such polarization states are promising tools for the fabrication of micro holes [5].Axially symmetric polarized laser radiation can be either generated intra-or extra-cavity. While the latter was realized at high average powers in the multi kW range, e.g. by means of segmented half-wave plates and a multimode input beam [5], the former has been demonstrated with different approaches such as customized fibers [6], a tripleaxicon retroreflector unit [7], the so-called Giant Reflection to Zero Order (GIRO) mirror [8] or grating mirrors [9,10]. Up to now the listed intra-cavity approaches were only demonstrated in continuous wave (CW) operation. To generate pulsed beams with axially-symmetric polarization states at high average power so far only the aforementioned segmented half-wave plates were used to transform an incident linearly polarized fundamental-mode laser beam into a radially or azimuthally polarized LG01* mode. 85 W of average output power and radially polarized pulses as short as 750 fs were, for instance, achieved by means of three cascaded single-crystal fiber (SCF) amplifier stages starting from a linearly polarized seed beam with an average power of 1.5 W [11]. The polarization conversion was implemented between the second and the third amplification stage. An even higher output power was demonstrated Abstract We report on a single-stage high-power amplification of a radially polarized mode-locked laser beam in a single-crystal fiber (SCF) amplifier. The seed beam was amplified by a factor of 5.0 to an average output power of 66.3 W. The pulse duration of the amplified pulses was measured to be 909 fs at a repetition rate of 40.7 MHz, corresponding to a pulse energy of 1.63 µJ and a resulting pulse peak power of 1.58 MW. The output beam showed a very high quality of the doughnut-shaped intensity distribution and furthermore a high radial polarization purity.
We report on the first demonstration of a radially polarized passively mode-locked thin-disk oscillator. Radial polarization was achieved by the use of a novel circular grating waveguide output coupler. We showed mode-locked operation up to a maximum average output power of 13.3 W with an optical efficiency of 21.8%. The degree of radial polarization of the emitted beam was measured to be 97±1%. The laser system generated pulses with a duration of 907 fs and an energy of 316 nJ corresponding to a peak power of 0.35 MW. To the best of our knowledge, these values exceed the performance of previously reported radially polarized mode-locked oscillator systems.
We report on a high-power passively mode-locked radially polarized Yb:YAG thin-disk oscillator providing 125 W of average output power. To the best of our knowledge, this is the highest average power ever reported from a mode-locked radially polarized oscillator without subsequent amplification stages. Mode-locking was achieved by implementing a SESAM as the cavity end mirror and the radial polarization of the LG* mode was obtained by means of a circular Grating Waveguide Output Coupler. The repetition rate was 78 MHz. A pulse duration of 0.97 ps and a spectral bandwidth of 1.4 nm (FWHM) were measured at the maximum output power. This corresponds to a pulse energy of 1.6 µJ and a pulse peak power of 1.45 MW. A high degree of radial polarization of 97.3 ± 1% and an M-value of 2.16 which is close to the theoretical value for the LG* doughnut mode were measured.
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