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- PublicationAccès libreCarrier-envelope offset frequency stabilization of a gigahertz semiconductor disk laserOptical frequency combs based on ultrafast lasers have enabled numerous scientific breakthroughs. However, their use for commercial applications is limited by the complexity and cost of femtosecond laser technology. Ultrafast semiconductor lasers might change this issue as they can be mass produced in a cost-efficient way while providing large spectral coverage from a single technology. However, it has not been proven to date if ultrafast semiconductor lasers are suitable for stabilization of their carrier-envelope offset (CEO) frequency. Here we present what we believe to be the first CEO frequency stabilization of an ultrafast semiconductor disk laser (SDL). The optically pumped SDL is passively modelocked by a semiconductor saturable absorber mirror. It operates at a repetition rate of 1.8 GHz and a center wavelength of 1034 nm. The 273 fs pulses of the oscillator are amplified to an average power level of 6 W and temporally compressed down to 120 fs. A coherent octave-spanning supercontinuum spectrum is generated in a photonic crystal fiber. The CEO frequency is detected in a standard ƒ–to–2ƒ interferometer and phase locked to an external reference by feedback applied to the current of the SDL pump diode. This proof-of-principle demonstrates that ultrafast SDLs are suitable for CEO stabilization and constitutes a key step for further developments of this comb technology expected in the coming years.
- PublicationAccès libreCarrier envelope offset frequency detection and stabilization of a diode-pumped mode-locked Ti:sapphire laserWe demonstrate the first diode-pumped Ti:sapphire laser frequency comb. It is pumped by two green laser diodes with a total pump power of 3 W. The Ti:sapphire laser generates 250 mW of average output power in 61-fs pulses at a repetition rate of 216 MHz. We generated an octave-spanning supercontinuum spectrum in a photonic-crystal fiber and detected the carrier envelope offset (CEO) frequency in a standard ƒ-to-2ƒ interferometer setup. We stabilized the CEO-frequency through direct current modulation of one of the green pump diodes with a feedback bandwidth of 55 kHz limited by the pump diode driver used in this experiment. We achieved a reduction of the CEO phase noise power spectral density by 140 dB at 1 Hz offset frequency. An advantage of diode pumping is the ability for high-bandwidth modulation of the pump power via direct current modulation. After this experiment, we studied the modulation capabilities and noise properties of green pump laser diodes with improved driver electronics. The current-to-output-power modulation transfer function shows a bandwidth larger than 1 MHz, which should be sufficient to fully exploit the modulation bandwidth of the Ti:sapphire gain for CEO stabilization in future experiments.
- PublicationAccès libreCarrier-envelope offset stabilization of a GHz repetition rate femtosecond laser using opto-optical modulation of a SESAMWe demonstrate, to the best of our knowledge, the first carrier-envelope offset (CEO) frequency stabilization of a GHz femtosecond laser based on opto-optical modulation (OOM) of a semiconductor saturable absorber mirror (SESAM). The 1.05-GHz laser is based on a Yb:CALGO gain crystal and emits sub-100-fs pulses with 2.1-W average power at a center wavelength of 1055 nm. The SESAM plays two key roles: it starts and stabilizes the mode-locking operation and is simultaneously used as an actuator to control the CEO frequency. This second functionality is implemented by pumping the SESAM with a continuous-wave 980-nm laser diode in order to slightly modify its nonlinear reflectivity. We use the standard ƒ-to-2ƒ method for detection of the CEO frequency, which is stabilized by applying a feedback signal to the current of the SESAM pump diode. We compare the SESAM-OOM stabilization with the traditional method of gain modulation via control of the pump power of the Yb:CALGO gain crystal. While the bandwidth for gain modulation is intrinsically limited to ∼250 kHz by the laser cavity dynamics, we show that the OOM provides a feedback bandwidth above 500 kHz. Hence, we were able to obtain a residual integrated phase noise of 430 mrad for the stabilized CEO beat, which represents an improvement of more than 30% compared to gain modulation stabilization.
- PublicationAccès libreFrequency Comb Stabilization of Ultrafast Lasers by Opto-Optical Modulation of SemiconductorsIn this paper, we review the current state and discuss new developments in opto-optical modulation (OOM) of semiconductor elements for frequency comb self-referenced stabilization of ultrafast lasers. This method has been successfully used for carrier-envelope offset (CEO) frequency stabilization of diodepumped solid-state lasers operating in 1-μm and 1.5-μm regimes, providing high feedback bandwidth and resulting in low noise performance. We compare the achieved results for Er- and Yb-based laser materials and in different regimes of repetition rates up to 1 GHz. In addition, we present the first semiconductor OOM for CEO stabilization in an ultrafast fiber laser. Moreover, we discuss requirements and design guidelines for OOM chips. In most demonstrations, semiconductor saturable absorber mirrors have been used for OOM, which in parallel were also responsible for pulse formation. By separating the OOM functionality from the pulse formation, we expect that it will enable low-noise CEO stabilization in other types of ultrafast lasers, such as, for example, high-power Kerr-lens mode-locked thin disk lasers.
- PublicationAccès libreFull stabilization and characterization of an optical frequency comb from a diode-pumped solid-state laser with GHz repetition rateWe demonstrate the first self-referenced full stabilization of a diode-pumped solid-state laser (DPSSL) frequency comb with a GHz repetition rate. The Yb:CALGO DPSSL delivers an average output power of up to 2.1 W with a typical pulse duration of 96 fs and a center wavelength of 1055 nm. A carrier-envelope offset (CEO) beat with a signal-to-noise ratio of 40 dB (in 10-kHz resolution bandwidth) is detected after supercontinuum generation and ƒ-to-2ƒ interferometry directly from the output of the oscillator, without any external amplification or pulse compression. The repetition rate is stabilized to a reference synthesizer with a residual integrated timing jitter of 249 fs [10 Hz – 1 MHz] and a relative frequency stability of 10−12/s. The CEO frequency is phase-locked to an external reference via pump current feedback using home-built modulation electronics. It achieves a loop bandwidth of ∼150 kHz, which results in a tight CEO lock with a residual integrated phase noise of 680 mrad [1 Hz – 1 MHz]. We present a detailed characterization of the GHz frequency comb that combines a noise analysis of the repetition rate ƒrep, of the CEO frequency ƒCEO, and of an optical comb line at 1030 nm obtained from a virtual beat with a narrow-linewidth laser at 1557 nm using a transfer oscillator. An optical comb linewidth of about 800 kHz is assessed at 1-s observation time, for which the dominant noise sources of ƒrep and ƒCEO are identified.
- PublicationAccès libreGreen-diode-pumped femtosecond Ti:Sapphire laser with up to 450 mW average powerWe 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.