Diode-pumped 45 fs Yb:CALGO laser oscillator with 1.7 MW of peak power

Growth, spectroscopy and SESAM mode-locking of a "mixed" Yb:Ca(Gd,Y)AlO4 disordered crystal

We present the growth, spectroscopy, continuous-wave (CW) and passively mode-locked (ML) operation of a novel "mixed" tetragonal calcium rare-earth aluminate crystal, Yb3+:Ca(Gd,Y)AlO4. The absorption, stimulated-emission, and gain cross-sections are derived for π and σ polarizations. The laser performance of a c-cut Yb:Ca(Gd,Y)AlO4 crystal is studied using a spatially single-mode, 976-nm fiber-coupled laser diode as a pump source. A maximum output power of 347 mW is obtained in the CW regime with a slope efficiency of 48.9%. The emission wavelength is continuously tunable across 90 nm (1010 - 1100 nm) using a quartz-based Lyot filter. With a commercial SEmiconductor Saturable Absorber Mirror to initiate and maintain ML operation, soliton pulses as short as 35 fs are generated at 1059.8 nm with an average output power of 51 mW at ∼65.95 MHz. The average output power can be scaled to 105 mW for slightly longer pulses of 42 fs at 1063.5 nm.

Semiconductor saturable absorber mirror mode-locked Yb:YAP laser

We report on sub-30 fs pulse generation from a semiconductor saturable absorber mirror mode-locked Yb:YAP laser. Pumping by a spatially single-mode Yb fiber laser at 979 nm, soliton pulses as short as 29 fs were generated at 1091 nm with an average output power of 156 mW and a pulse repetition rate of 85.1 MHz. The maximum output power of the mode-locked Yb:YAP laser amounted to 320 mW for slightly longer pulses (32 fs) at an incident pump power of 1.52 W, corresponding to a peak power of 103 kW and an optical efficiency of 20.5%. To the best of our knowledge, this result represents the shortest pulses ever achieved from any solid-state Yb laser mode-locked by a slow, i.e., physical saturable absorber.

Efficient high-power sub-50-fs gigahertz repetition rate diode-pumped solid-state laser

In this article we present a directly diode-pumped high-power Kerr-lens mode-locked Yb:CALGO bulk laser oscillator operating at 1-GHz repetition rate. We report on two laser configurations optimized for either highest average power or shortest pulse duration. In the first configuration optimized for high average power, the oscillator delivers up to 6.9 W of average power, which is the highest average power of any ultrafast laser oscillator operating at gigahertz repetition rate. The 93-fs pulses have a peak power of 64 kW, and the optical-to-optical efficiency amounts to 37%. In the second configuration optimized for short pulse duration, we demonstrate 48-fs pulses at 4.1 W of average power corresponding to a higher peak power of 74 kW with 21% optical-to-optical efficiency. This is the shortest pulse duration and the highest peak power demonstrated by any GHz-class Yb-based laser oscillator. The compact laser setup is directly pumped by a low-cost multimode fiber-coupled laser diode and has a high potential as an economical yet powerful source for various applications.

Semiconductor saturable absorber mirror mode-locked Yb:YLF laser with pulses of 40 fs

We have generated pulses as short as 40 fs with an average power of 265 mW from a semiconductor saturable absorber mirror (SESAM) mode-locked Yb:YLF oscillator employing a 1% transmitting output coupler (OC). The room-temperature laser is pumped by a low-cost 960 nm single-emitter multimode diode and dispersion compensation is provided via double chirped mirrors (DCMs). The 40-fs pulses are centered around 1050 nm with a width of 34 nm at a repetition rate of 87.3 MHz. By increasing the output coupling to 5% and by using Gires-Tournois interferometer (GTI) mirrors for dispersion compensation, we have also demonstrated 380-fs pulses with 1.85 W of average power around 1025 nm at a repetition rate of 190.4 MHz. Using an intracavity off-surface optic axis birefringent filter, the central wavelength of the pulses could be tuned in the 1020-1025 nm and 1019-1047 nm ranges for the 5% and 1% transmitting OCs, respectively. To the best of our knowledge, these are the shortest pulses and highest average and peak powers generated from room-temperature Yb:YLF lasers to date.

Efficient few-cycle Yb-doped laser oscillator with Watt-level average power

So far, the operation of ultrafast bulk laser oscillators based on Yb-doped gain materials and directly emitting few-cycle pulses have been restricted to low optical-to-optical efficiencies and average output powers of only a few milliwatt. This performance limitation can be attributed to the commonly-applied standard collinear pumping scheme in which the optical pump is transmitted through a dichroic mirror whose spectral transmission and dispersion properties severely perturb the oscillating pulse when its optical spectrum extends towards the pump wavelength. In this study, we report on a novel pumping scheme relying on cross polarization that overcomes this challenge. In our concept, the pump transmitting mirror is highly transmissive for the pump light in p-polarization, while it is highly reflective for the laser light in s-polarization over a broad wavelength range, even covering the pump wavelength and beyond. In contrast to a standard thin-film polarizer featuring similar polarization dependent properties, it provides a low and flat dispersion profile over a broad spectral range for the s-polarization. Implementing this pumping scheme in a soft-aperture Kerr-lens mode-locked bulk laser oscillator based on the gain material Yb:CALGO, we achieve clean 22-fs soliton pulses at 729 mW of average output power and an optical-to-optical efficiency of 25%. In a second configuration optimized for the highest average output power, we demonstrate a high optical-to-optical efficiency of 36.6%, which was obtained for 31-fs pulses at 1.63 W of average output power. In a third configuration we experimentally confirm the limiting effect of a dichroic mirror commonly used in the standard collinear pumping scheme. All the results presented here and obtained in the first and second configuration generate pulses with a center wavelength ranging from 1030 nm to 1056 nm, well within the spectral region of high gain cross sections of Yb:CALGO. While this initial demonstration was realized using a commercial diffraction-limited fiber laser as pump source, the pump geometry appears also well suited for pumping with laser diodes coupled into multimode fibers. This novel approach opens up new opportunities for compact and cost-efficient high-power few-cycle bulk laser oscillators based on Yb-doped gain materials and can be applied to any gain material with small quantum defect.

Advances of Yb:CALGO Laser Crystals

Yb:CaGdAlO4, or Yb:CALGO, a new laser crystal, has been attracting increasing attention recently in a myriad of laser technologies. This crystal features salient thermal, spectroscopic and mechanical properties, which enable highly efficient and safe generation of continuous-wave radiations and ultrafast pulses with ever short durations. More specifically, its remarkable thermal-optic property and its high conversion efficiency allow high-power operation. Its high nonlinear coefficient facilitates study of optimized mode locking lasers. Besides, its ultrabroad and flat-top emission band benefits the generation of complex structured light with outstanding tunability. In this paper, we review the recent advances in the study of Yb:CALGO, covering its physical properties as well as its growing applications in various fields and prospect for future development.

17.8 fs broadband Kerr-lens mode-locked Yb:CALGO oscillator

Pulses as short as 17.8 fs with a spectral bandwidth of 145 nm and central wavelength of 1118 nm have been generated from a Kerr-lens mode-locked Yb:CALGO oscillator. The oscillator operating at an average power of 26 mW and a repetition rate of 95.9 MHz is pumped by a cost-effective single-mode fiber coupled laser diode emitting 800 mW at 976 nm. The dispersion is compensated using a prism pair combined with broadband chirp mirrors. To the best of our knowledge, the pulse durations corresponding to approximately 4.8 optical cycle pulses are the shortest achieved durations through a Yb-doped bulk oscillator.

10-W-scale Kerr-lens mode-locked Yb:CALYO laser with sub-100-fs pulses

We reported a high-power pure Kerr-lens mode-locked Yb:CALYO laser based on the dual-confocal cavity delivering sub-100-fs pulses. The output pulses at 81 MHz have an average power of 10.4 W and the pulse duration of 98 fs, corresponding to the peak power of 1.14 MW. This is, to the best of our knowledge, the highest average power ever reported for a Kerr-lens mode-locked Yb-bulk oscillator. Analysis of the dual-confocal cavity was also conducted, which indicates a way to achieve higher average power. We believe the result described in this Letter may pave a way to develop Kerr-lens mode-locked bulk lasers with much higher average power.

Wavelength shift with a diode-pumped continuous-wave Yb:CALGO laser

The dependence of an emission wavelength on the crystal temperature was first investigated for a diode-pumped continuous-wave ${{\rm Yb}^{3 + }}$Yb³⁺-doped ${{\rm CaGdAlO}_4}$CaGdAlO₄ (Yb:CALGO) laser. A maximum output power of 11 W was obtained, corresponding to a slope efficiency of 19.8%. The output wavelength varied from 1051.10 nm to 1054.72 nm with increased absorbed pump power. This wavelength shift is attributed to a change in the crystal temperature. This observation is, to our best knowledge, an original conclusion about this phenomenon in a Yb:CALGO laser. We use a temperature-dependent model to explain the emission wavelength shifts that can be generalized to any such quasi-three-level materials.

Diode-pumped high-power sub-100 fs Kerr-lens mode-locked Yb:CaYAlO4 laser with 1.85 MW peak power

We demonstrated a diode-pumped high-power Kerr-lens mode-locked Yb:CaYAlO₄ (Yb:CALYO) laser with a dual-confocal cavity, directly generating 59-fs pulses with 6.2 W average power, which is the highest average power from any sub-60 fs Yb-doped solid-state lasers. With the repetition rate of 50 MHz, the corresponding single pulse energy was 124 nJ and the peak power was 1.85 MW, which to the best of our knowledge is the highest peak power delivered directly from a sub-100 fs Yb-based bulk lasers ever.

Sub-100-fs Kerr lens mode-locked Yb:Lu2O3 thin-disk laser oscillator operating at 21 W average power

We investigate power-scaling of a Kerr lens mode-locked (KLM) Yb:Lu₂O₃ thin-disk laser (TDL) oscillator operating in the sub-100-fs pulse duration regime. Employing a scheme with higher round-trip gain by increasing the number of passes through the thin-disk gain element, we increase the average power by a factor of two and the optical-to-optical efficiency by a factor of almost three compared to our previous sub-100-fs mode-locking results. The oscillator generates pulses with a duration of 95 fs at 21.1 W average power and 47.9 MHz repetition rate. We discuss the cavity design for continuous-wave and mode-locked operation and the estimation of the focal length of the Kerr lens. Unlike to usual KLM TDL oscillators, an operation at the edge of the stability zone in continuous-wave operation is not required. This work shows that KLM TDL oscillators based on the gain material Yb:Lu₂O₃ are an excellent choice for power-scaling of laser oscillators in the sub-100-fs regime, and we expect that such lasers will soon operate at power levels in excess of hundred watts.

Periodic-trajectory-controlled, coherent-state-phase-switched, and wavelength-tunable SU(2) geometric modes in a frequency-degenerate resonator

We report a method to realize the periodic trajectory controlling, coherent-state phase switching, and wavelength tuning of SU(2) geometric modes (GMs) in a frequency-degenerate resonator (FDR). FDR is a resonator in which the ratio of transverse and longitude modes frequency spacing is a simple rational number, which would lead to a laser wave-packet in a SU(2) coherent state related to a periodic ray trajectory. We demonstrate that the periodic trajectory can be switched with coherent-state phase changing from 0 to π (or π to 0) by simply controlling the position of gain medium in the same FDR. For the period-of-four state, the geometries are switched between "W" and "M" shapes. For the period-of-three state, those are switched between "IV" and "VI" shapes. Moreover, because a special crystal Yb:CALGO with extremely broad emission band is used as the gain medium, our SU(2) GMs have the wavelength-tunable property in contrast to the conventional single-frequency GMs. The center wavelength can be tuned with the range of about 10 nm by adjusting the pump power. These effects can further enrich the various applications of structured light manipulation.