The Experts below are selected from a list of 360 Experts worldwide ranked by ideXlab platform
Thomas Graf - One of the best experts on this subject based on the ideXlab platform.
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highly efficient 400 w near fundamental mode green thin disk Laser
Optics Letters, 2016Co-Authors: Stefan Piehler, Thomas Graf, Tom Dietrich, Martin Rumpel, Marwan Abdou AhmedAbstract:We report on the efficient generation of continuous-wave, high-brightness green Laser radiation. Green Lasers are particularly interesting for reliable and reproducible deep-penetration welding of copper or for pumping Ti:Sa oscillators. By intracavity second-harmonic generation in a thin-disk Laser Resonator designed for fundamental-mode operation, an output power of up to 403 W is demonstrated at a wavelength of 515 nm with almost diffraction-limited beam quality. The unprecedented optical efficiency of 40.7% of green output power with respect to the pump power of the thin-disk Laser is enabled by the intracavity use of a highly efficient grating waveguide mirror, which combines the functions of wavelength stabilization and spectral narrowing, as well as polarization selection in a single element.
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investigations on ring shaped pumping distributions for the generation of beams with radial polarization in an yb yag thin disk Laser
Optics Express, 2015Co-Authors: Tom Dietrich, Thomas Graf, Martin Rumpel, Marwan Abdou AhmedAbstract:We present experimental investigations on the generation of radially polarized Laser beams excited by a ring-shaped pump intensity distribution in combination with polarizing grating waveguide mirrors in an Yb:YAG thin-disk Laser Resonator. Hollow optical fiber components were implemented in the pump beam path to transform the commonly used flattop pumping distribution into a ring-shaped distribution. The investigation was focused on finding the optimum mode overlap between the ring-shaped pump spot and the excited first order Laguerre-Gaussian (LG(01)) doughnut mode. The power, efficiency and polarization state of the emitted Laser beam as well as the thermal behavior of the disk was compared to that obtained with a standard flattop pumping distribution. A maximum output power of 107 W with a high optical efficiency of 41.2% was achieved by implementing a 300 mm long specially manufactured hollow fiber into the pump beam path. Additionally it was found that at a pump power of 280 W the maximum temperature increase is about 21% below the one observed with standard homogeneous pumping.
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single layer resonant waveguide grating for polarization and wavelength selection in yb yag thin disk Lasers
Optics Express, 2012Co-Authors: Moritz M Vogel, Andreas Voss, Marwan Abdou Ahmed, Martin Rumpel, Birgit Weichelt, Matthias Haefner, Christof Pruss, Wolfgang Osten, Thomas GrafAbstract:A single-layer resonant-waveguide grating consisting of a sub-wavelength grating coupler etched into a waveguide is proposed in order to achieve high polarization and high spectral selectivity inside an Yb:YAG thin-disk Laser Resonator. The designed structure was fabricated with the help of a Lloyd's-mirror interference lithography setup followed by reactive ion beam etching down to the desired grating groove depth. The wavelength and polarization dependent reflectivity is measured and compared to the design results. The behaviour of the device at higher temperatures is also investigated in the present work. The device is introduced as the end mirror of an Yb:YAG thin-disk Laser cavity. Output powers of up to 123 W with a spectral bandwidth of about 0.5 nm (FWHM) is demonstrated in a multimode configuration (M2~6). In fundamental-mode operation (TEM00 with M2~1.1) 70 W of power with a spectral bandwidth of about 20 pm have been obtained. Moreover, the degree of linear polarization was measured to be higher than 99% for both multimode and fundamental mode operation.
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multilayer polarizing grating mirror used for the generation of radial polarization in yb yag thin disk Lasers
Optics Letters, 2007Co-Authors: Marwan Abdou Ahmed, Andreas Voss, Moritz M Vogel, Thomas GrafAbstract:The design, fabrication and characterization of a multilayer polarizing grating mirror developed for an Yb:YAG thin-disk Laser Resonator are reported. The potential of the proposed solution is discussed together with the first demonstration of a radially polarized Yb:YAG thin-disk Laser.
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extension of the jones matrix formalism to higher order transverse modes
Optics Letters, 2007Co-Authors: Andreas Voss, Marwan Abdou Ahmed, Thomas GrafAbstract:The well-known Jones matrix formalism, which can be directly applied to the propagation of the polarization of fundamental (TEM(00)) Laser Resonator modes, has to be modified for higher-order transverse modes. It is shown that this can be done in straightforward manner by using N x N matrices instead of the 2 x 2 Jones matrices, where N denotes the number of orthogonal polarization states of the transverse mode under consideration. The most common case of TEM(01) Hermite-Gaussian modes, where N is four, is discussed in detail.
Brett E Bouma - One of the best experts on this subject based on the ideXlab platform.
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extended coherence length and depth ranging using a fourier domain mode locked frequency comb and circular interferometric ranging
Physical review applied, 2019Co-Authors: Norman Lippok, Benjamin J Vakoc, Brett E Bouma, Meena SiddiquiAbstract:Fourier domain mode-locking (FDML) has been a popular Laser design for high speed optical frequency domain imaging (OFDI) but the achievable coherence length, and therefore imaging range, has been limited. The narrow instantaneous linewidth of a frequency comb (FC) FDML Laser could provide an attractive platform for high speed as well as long range OFDI. Unfortunately, aliasing artifacts arising from signals beyond the principle measurement depth of the free spectral range have prohibited the use of a FC FDML for imaging so far. To make the enhanced coherence length of FC FDML Laser available, methods to manage such artifacts are required. Recently, coherent circular ranging has been demonstrated that uses frequency combs for imaging in much reduced RF bandwidths. Here, we revisit circular ranging as a tool of making the long coherence length of an FDML frequency comb Laser as well as its use for tissue imaging accessible. Using an acousto-optic frequency shifter (AOFS), we describe an active method to mitigate signal aliasing that is both stable and wavelength independent. We show that an FC FDML Laser offers an order of magnitude improved coherence length compared to traditional FDML Laser designs without requiring precise dispersion engineering. We discuss design parameters of a frequency stepping Laser Resonator as well as aliasing from a frequency comb and AOFS in OFDI with numerical simulations. The use of circular ranging additionally reduced acquisition bandwidths 15-fold compared with traditional OFDI methods. The FC FDML/AOFS design offers a convenient platform for long range and high speed imaging as well as exploring signal and image processing methods in circular ranging.
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extended coherence length and depth ranging using a fourier domain mode locked frequency comb and circular interferometric ranging
arXiv: Optics, 2018Co-Authors: Norman Lippok, Benjamin J Vakoc, Brett E Bouma, Meena SiddiquiAbstract:Fourier domain mode-locking (FDML) has been a popular Laser design for high speed optical frequency domain imaging (OFDI) but achieving long coherence lengths, and therefore imaging range, has been challenging. The narrow instantaneous linewidth of a frequency comb (FC) FDML Laser could provide an attractive platform for high speed as well as long range OFDI. Unfortunately, aliasing artifacts arising from signals beyond the principle measurement depth of the free spectral range have prohibited the use of a FC FDML for imaging so far. To make the enhanced coherence length of FC FDML Laser available, methods to manage such artifacts are required. Recently, coherent circular ranging has been demonstrated that uses frequency combs for imaging in much reduced RF bandwidths. Here, we revisit circular ranging as a tool of making the long coherence length of an FDML frequency comb Laser as well as its use for tissue imaging accessible. Using an acousto-optic frequency shifter (AOFS), we describe an active method to mitigate signal aliasing that is both stable and wavelength independent. We show that an FC FDML Laser offers an order of magnitude improved coherence length compared to traditional FDML Laser designs without requiring precise dispersion engineering. We discuss design parameters of a frequency stepping Laser Resonator as well as aliasing from a frequency comb and AOFS in OFDI with numerical simulations. The use of circular ranging additionally reduced acquisition bandwidths 15-fold compared with traditional OFDI methods. The FC FDML/AOFS design offers a convenient platform for long range and high speed imaging as well as exploring signal and image processing methods in circular ranging.
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ultrahigh speed optical frequency domain imaging and application to Laser ablation monitoring
Applied Physics Letters, 2006Co-Authors: Seok Hyun Yun, Benjamin J Vakoc, Guillermo J Tearney, Brett E BoumaAbstract:We demonstrate a linear Laser Resonator incorporating a semiconductor optical amplifier and scanning filter for high repetition rate, broad wavelength, unidirectional scanning. The Laser operates at up to 115kHz repetition rates and demonstrates a tuning-speed-independent power of >30mW. We apply this Laser to enable ultrahigh-speed optical frequency domain imaging of the dynamics of Laser ablation of biological tissue. The imaging system acquires single longitudinal scans (A-lines) in 8.7μs and complete cross-sectional images comprising 575A-lines at a rate of 200 frames per second.
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high speed wavelength swept semiconductor Laser with a polygon scanner based wavelength filter
Optics Letters, 2003Co-Authors: Caroline Boudoux, Guillermo J Tearney, Brett E BoumaAbstract:Ultrahigh-speed tuning of an extended-cavity semiconductor Laser is demonstrated. The Laser Resonator comprises a unidirectional fiber-optic ring, a semiconductor optical amplifier as the gain medium, and a novel scanning filter based on a polygonal scanner. Variable tuning rates up to 1150 nm/ms (15.7-kHz repetition frequency) are demonstrated over a 70-nm wavelength span centered at 1.32μm . This tuning rate is more than an order of magnitude faster than previously demonstrated and is facilitated in part by self-frequency shifting in the semiconductor optical amplifier. The instantaneous linewidth of the source is <0.1 nm for 9-mW cw output power and a low spontaneous-emission background of -80 dB .
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low repetition rate high peak power kerr lens mode locked ti al 2 o 3 Laser with a multiple pass cavity
Optics Letters, 1999Co-Authors: S H Cho, Brett E Bouma, E P Ippen, James G FujimotoAbstract:We demonstrate a novel, long, multiple-pass cavity (MPC) to obtain low repetition rates and high peak intensities from Kerr-lens mode-locked Lasers. We show that the MPC provides a zero effective length by a unity transformation of the q parameter after a given number of transits of the Laser beam. Pulse durations of 16.5??fs with 0.7??MW of power at a 15-MHz repetition rate are achieved. This is, to our knowledge, the lowest repetition rate ever achieved directly from a femtosecond Laser Resonator without use of additional active devices and cavity dumping. The combination of low repetition rates and high peak intensity is extremely useful for femtosecond pump–probe and other nonlinear experiments because it permits the application of high peak intensity without excessive average power.
Marwan Abdou Ahmed - One of the best experts on this subject based on the ideXlab platform.
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highly efficient 400 w near fundamental mode green thin disk Laser
Optics Letters, 2016Co-Authors: Stefan Piehler, Thomas Graf, Tom Dietrich, Martin Rumpel, Marwan Abdou AhmedAbstract:We report on the efficient generation of continuous-wave, high-brightness green Laser radiation. Green Lasers are particularly interesting for reliable and reproducible deep-penetration welding of copper or for pumping Ti:Sa oscillators. By intracavity second-harmonic generation in a thin-disk Laser Resonator designed for fundamental-mode operation, an output power of up to 403 W is demonstrated at a wavelength of 515 nm with almost diffraction-limited beam quality. The unprecedented optical efficiency of 40.7% of green output power with respect to the pump power of the thin-disk Laser is enabled by the intracavity use of a highly efficient grating waveguide mirror, which combines the functions of wavelength stabilization and spectral narrowing, as well as polarization selection in a single element.
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investigations on ring shaped pumping distributions for the generation of beams with radial polarization in an yb yag thin disk Laser
Optics Express, 2015Co-Authors: Tom Dietrich, Thomas Graf, Martin Rumpel, Marwan Abdou AhmedAbstract:We present experimental investigations on the generation of radially polarized Laser beams excited by a ring-shaped pump intensity distribution in combination with polarizing grating waveguide mirrors in an Yb:YAG thin-disk Laser Resonator. Hollow optical fiber components were implemented in the pump beam path to transform the commonly used flattop pumping distribution into a ring-shaped distribution. The investigation was focused on finding the optimum mode overlap between the ring-shaped pump spot and the excited first order Laguerre-Gaussian (LG(01)) doughnut mode. The power, efficiency and polarization state of the emitted Laser beam as well as the thermal behavior of the disk was compared to that obtained with a standard flattop pumping distribution. A maximum output power of 107 W with a high optical efficiency of 41.2% was achieved by implementing a 300 mm long specially manufactured hollow fiber into the pump beam path. Additionally it was found that at a pump power of 280 W the maximum temperature increase is about 21% below the one observed with standard homogeneous pumping.
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single layer resonant waveguide grating for polarization and wavelength selection in yb yag thin disk Lasers
Optics Express, 2012Co-Authors: Moritz M Vogel, Andreas Voss, Marwan Abdou Ahmed, Martin Rumpel, Birgit Weichelt, Matthias Haefner, Christof Pruss, Wolfgang Osten, Thomas GrafAbstract:A single-layer resonant-waveguide grating consisting of a sub-wavelength grating coupler etched into a waveguide is proposed in order to achieve high polarization and high spectral selectivity inside an Yb:YAG thin-disk Laser Resonator. The designed structure was fabricated with the help of a Lloyd's-mirror interference lithography setup followed by reactive ion beam etching down to the desired grating groove depth. The wavelength and polarization dependent reflectivity is measured and compared to the design results. The behaviour of the device at higher temperatures is also investigated in the present work. The device is introduced as the end mirror of an Yb:YAG thin-disk Laser cavity. Output powers of up to 123 W with a spectral bandwidth of about 0.5 nm (FWHM) is demonstrated in a multimode configuration (M2~6). In fundamental-mode operation (TEM00 with M2~1.1) 70 W of power with a spectral bandwidth of about 20 pm have been obtained. Moreover, the degree of linear polarization was measured to be higher than 99% for both multimode and fundamental mode operation.
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multilayer polarizing grating mirror used for the generation of radial polarization in yb yag thin disk Lasers
Optics Letters, 2007Co-Authors: Marwan Abdou Ahmed, Andreas Voss, Moritz M Vogel, Thomas GrafAbstract:The design, fabrication and characterization of a multilayer polarizing grating mirror developed for an Yb:YAG thin-disk Laser Resonator are reported. The potential of the proposed solution is discussed together with the first demonstration of a radially polarized Yb:YAG thin-disk Laser.
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extension of the jones matrix formalism to higher order transverse modes
Optics Letters, 2007Co-Authors: Andreas Voss, Marwan Abdou Ahmed, Thomas GrafAbstract:The well-known Jones matrix formalism, which can be directly applied to the propagation of the polarization of fundamental (TEM(00)) Laser Resonator modes, has to be modified for higher-order transverse modes. It is shown that this can be done in straightforward manner by using N x N matrices instead of the 2 x 2 Jones matrices, where N denotes the number of orthogonal polarization states of the transverse mode under consideration. The most common case of TEM(01) Hermite-Gaussian modes, where N is four, is discussed in detail.
Andreas Voss - One of the best experts on this subject based on the ideXlab platform.
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single layer resonant waveguide grating for polarization and wavelength selection in yb yag thin disk Lasers
Optics Express, 2012Co-Authors: Moritz M Vogel, Andreas Voss, Marwan Abdou Ahmed, Martin Rumpel, Birgit Weichelt, Matthias Haefner, Christof Pruss, Wolfgang Osten, Thomas GrafAbstract:A single-layer resonant-waveguide grating consisting of a sub-wavelength grating coupler etched into a waveguide is proposed in order to achieve high polarization and high spectral selectivity inside an Yb:YAG thin-disk Laser Resonator. The designed structure was fabricated with the help of a Lloyd's-mirror interference lithography setup followed by reactive ion beam etching down to the desired grating groove depth. The wavelength and polarization dependent reflectivity is measured and compared to the design results. The behaviour of the device at higher temperatures is also investigated in the present work. The device is introduced as the end mirror of an Yb:YAG thin-disk Laser cavity. Output powers of up to 123 W with a spectral bandwidth of about 0.5 nm (FWHM) is demonstrated in a multimode configuration (M2~6). In fundamental-mode operation (TEM00 with M2~1.1) 70 W of power with a spectral bandwidth of about 20 pm have been obtained. Moreover, the degree of linear polarization was measured to be higher than 99% for both multimode and fundamental mode operation.
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multilayer polarizing grating mirror used for the generation of radial polarization in yb yag thin disk Lasers
Optics Letters, 2007Co-Authors: Marwan Abdou Ahmed, Andreas Voss, Moritz M Vogel, Thomas GrafAbstract:The design, fabrication and characterization of a multilayer polarizing grating mirror developed for an Yb:YAG thin-disk Laser Resonator are reported. The potential of the proposed solution is discussed together with the first demonstration of a radially polarized Yb:YAG thin-disk Laser.
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extension of the jones matrix formalism to higher order transverse modes
Optics Letters, 2007Co-Authors: Andreas Voss, Marwan Abdou Ahmed, Thomas GrafAbstract:The well-known Jones matrix formalism, which can be directly applied to the propagation of the polarization of fundamental (TEM(00)) Laser Resonator modes, has to be modified for higher-order transverse modes. It is shown that this can be done in straightforward manner by using N x N matrices instead of the 2 x 2 Jones matrices, where N denotes the number of orthogonal polarization states of the transverse mode under consideration. The most common case of TEM(01) Hermite-Gaussian modes, where N is four, is discussed in detail.
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multiwatt diode pumped yb yag thin disk Laser continuously tunable between 1018 and 1053 nm
Optics Letters, 1995Co-Authors: U Brauch, Adolf Giesen, M Karszewski, Chr Stewen, Andreas VossAbstract:A new powerful source of broadly (35-nm) tunable Laser radiation in the near-infrared (near 1030 nm) wavelength range is presented. Inserting a birefringent filter into a 10-W diode-pumped Yb:YAG thin disk Laser Resonator gives several watts of narrow-linewidth (0.07-nm) continuously tunable cw output power. By taking advantage of the power scalability of the thin disk concept, even hundreds of watts of tunable power with near-diffraction-limited beam quality and high efficiency are feasible. Generation and amplification of subpicosecond pulses with high average and peak powers are also promising applications of the Yb:YAG thin disk Laser.
V G Savitski - One of the best experts on this subject based on the ideXlab platform.
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pulsed kgd wo4 2 raman Laser towards emission linewidth narrowing
Devices and Methods of Measurements, 2015Co-Authors: V G SavitskiAbstract:The linewidth of a KGd(WO4)2 pulsed Raman Laser is analysed experimentally for different configurations of the Raman and pump Resonators: with narrow and broadband pump emission profiles, with and without linewidth narrowing elements in the Raman Laser Resonator, with and without injection seeding into the Raman cavity. The benefits of a narrow linewidth pump source in combination with linewidth narrowing elements in the Raman Laser cavity for the efficient linewidth narrowing of the Raman emission are explained. 20 kW peak-power pulses at 1156 nm with 0,43 cm -1 emission linewidth are demonstrated from an injection seeded KGW Raman Laser.
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experimental analysis of emission linewidth narrowing in a pulsed kgd wo4 2 raman Laser
Optics Express, 2014Co-Authors: V G SavitskiAbstract:The linewidth of a KGd(WO4)2 (KGW) intracavity pumped Raman Laser is analyzed experimentally for different configurations of the Raman and pump Laser Resonators: with narrow and broadband pump emission profiles, with and without linewidth narrowing elements in the Raman Laser Resonator, with and without injection seeding into the Raman cavity. The benefits of a narrow linewidth pump source in combination with linewidth narrowing elements in the Raman Laser cavity for the efficient linewidth narrowing of the Raman Laser emission are explained. 20 kW peak-power pulses at 1156 nm with 0.43 cm−1 emission linewidth are demonstrated from an injection seeded KGW Raman Laser.
