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Hoffmann, Martin
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Hoffmann, Martin
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- PublicationAccès libreUltrafast optical parametric oscillator pumped by a vertical external-cavity surface-emitting laser (VECSEL)(2017)
; ; ; ; - PublicationAccès libreGreen-diode-pumped femtosecond Ti:Sapphire laser with up to 450 mW average power(2015)
; ; ; ; We investigate power-scaling of green-diode-pumped Ti:Sapphire lasers in continuous-wave (CW) and mode-locked operation. In a first configuration with a total pump power of up to 2 W incident onto the crystal, we achieved a CW power of up to 440 mW and self-starting mode-locking with up to 200 mW average power in 68-fs pulses using semiconductor saturable absorber mirror (SESAM) as saturable absorber. In a second configuration with up to 3 W of pump power incident onto the crystal, we achieved up to 650 mW in CW operation and up to 450 mW in 58-fs pulses using Kerr-lens mode-locking (KLM). The shortest pulse duration was 39 fs, which was achieved at 350 mW average power using KLM. The mode-locked laser generates a pulse train at repetition rates around 400 MHz. No complex cooling system is required: neither the SESAM nor the Ti:Sapphire crystal is actively cooled, only air cooling is applied to the pump diodes using a small fan. Because of mass production for laser displays, we expect that prices for green laser diodes will become very favorable in the near future, opening the door for low-cost Ti:Sapphire lasers. This will be highly attractive for potential mass applications such as biomedical imaging and sensing. - PublicationMétadonnées seulementExperimentally verified pulse formation model for high-power femtosecond VECSELs(2013)
; ; ; Keller, Ursula - PublicationAccès libreExperimentally verified pulse formation model for high-power femtosecond VECSELs(2013)
; ; ; Keller, UrsulaOptically pumped vertical-external-cavity surface-emitting lasers (OP-VECSELs), passively modelocked with a semiconductor saturable absorber mirror (SESAM), have generated the highest average output power from any sub-picosecond semiconductor laser. Many applications, including frequency comb synthesis and coherent supercontinuum generation, require pulses in the sub-300-fs regime. A quantitative understanding of the pulse formation mechanism is required in order to reach this regime while maintaining stable, high-average-power performance. We present a numerical model with which we have obtained excellent quantitative agreement with two recent experiments in the femtosecond regime, and we have been able to correctly predict both the observed pulse duration and the output power for the first time. Our numerical model not only confirms the soliton-like pulse formation in the femtosecond regime, but also allows us to develop several clear guidelines to scale the performance toward shorter pulses and higher average output power. In particular, we show that a key VECSEL design parameter is a high gain saturation fluence. By optimizing this parameter, 200-fs pulses with an average output power of more than 1 W should be possible. - PublicationMétadonnées seulementHigh-power integrated ultrafast semiconductor disk laser: multi-Watt 10 GHz pulse generation(2012)
; ; ; Keller, Ursula - PublicationMétadonnées seulementVECSEL gain characterization(2012)
; ; ; Keller, Ursula - PublicationMétadonnées seulementLow repetition rate SESAM modelocked VECSEL using an extendable active multipass-cavity approach(2012)
; ; - PublicationAccès libreHigh-power integrated ultrafast semiconductor disk laser: multi-Watt 10 GHz pulse generation(2012)
; ; ; Keller, UrsulaPresented is an optically pumped modelocked integrated externalcavity surface emitting laser (MIXSEL) with a pulse repetition rate of 10 GHz, generating picosecond pulses at 2.4 W average output power at a centre wavelength of 963 nm. The MIXSEL structure integrates both the absorber and the gain layers within the same wafer. The saturable absorber is a single layer of self-assembled InAs quantum dots (QD) and the gain is obtained with seven InGaAs quantum wells. It is shown that the picosecond pulse duration is limited by the slow recovery time of the integrated QD saturable absorber. - PublicationAccès libreVECSEL gain characterization(2012)
; ; ; Keller, UrsulaWe present the first full gain characterization of two vertical external cavity surface emitting laser (VECSEL) gain chips with similar designs operating in the 960-nm wavelength regime. We optically pump the structures with continuous-wave (cw) 808-nm radiation and measure the nonlinear reflectivity for 130-fs and 1.4-ps probe pulses as function of probe pulse fluence, pump power, and heat sink temperature. With this technique we are able to measure the saturation behavior for VECSEL gain chips for the first time. The characterization with 1.4-ps pulses resulted in saturation fluences of 40-80 µJ/cm2, while probing with 130-fs pulses yields reduced saturation fluences of 30-50 µJ/cm2 for both structures. For both pulse durations this is lower than previously assumed. A small-signal gain of up to 5% is obtained with this technique. Furthermore, in a second measurement setup, we characterize the spectral dependence of the gain using a tunable cw probe beam. We measure a gain bandwidth of over 26 nm for both structures, full width at half maximum. - PublicationAccès libreLow repetition rate SESAM modelocked VECSEL using an extendable active multipass-cavity approach(2012)
; ; ; Keller, UrsulaUltrafast VECSELs are compact pulsed laser sources with more flexibility in the emission wavelength compared to diode-pumped solid-state lasers. Typically, the reduction of the pulse repetition rate is a straightforward method to increase both pulse energy and peak power. However, the relatively short carrier lifetime of semiconductor gain materials of a few nanoseconds sets a lower limit to the repetition rate of passively modelocked VECSELs. This fast gain recovery combined with low pulse repetition rates leads to the buildup of multiple pulses in the cavity. Therefore, we applied an active multipass approach with which demonstrate fundamental modelocking at a repetition rate of 253 MHz with 400 mW average output power in 11.3 ps pulses.