Sub-100-fs Yb:CALGO nonlinear regenerative amplifier

Dual-slab Yb:KGd(WO4)2 regenerative amplifier for spectral shaping and high-power output

A high-power regenerative amplifier (RA) based on dual-slab Yb:KGd(WO4)2 (Yb:KGW) was demonstrated, which provided a maximum average power of 33.7 W at a repetition rate of 75-200 kHz before compression with a central wavelength of 1039 nm, corresponding to an optical-to-optical conversion efficiency of 51.4%. To the best of our knowledge, this is the highest average power from the Yb:KGW solid-state RA. The compressed pulse duration of 205 fs was realized under the maximum output power. By adjusting the gain of the crystals, respectively, the spectral shaping can be achieved. A combination spectrum with root-mean-square (RMS) bandwidth of 4.5 nm was generated with a central wavelength of 1035 nm at an output power of 20 W, the compressed pulse duration was 159 fs. Meanwhile, effective mitigation of thermal effects by dual-slab configuration guaranteed the nearly diffraction-limited beam quality: M x2 = 1.17 and M y2 = 1.20.

417 W, 2.38 mJ Innoslab amplifier compressible to a high pulse quality of 406 fs

We demonstrate a 417 W, 175 kHz Innoslab chirped pulse amplification laser compressible to short and clean 406 fs pulse duration. A spectral bandwidth (full width at half maximum, FWHM) of ∼3 nm was maintained at full pump power, and the pulses exhibited good pulse quality in a wide tunable pulse energy range from 1.7 mJ to a maximum of 2.38 mJ. At the maximum output power, the compressed pulses were nearly pedestal free. The comprehensive effects of residual high-order dispersion from the front end, the gain shaping effects of the amplifier, and the slight mismatch of third-order dispersion (TOD) between the stretcher (CFBG) and the gating compressor, along with the small nonlinear phase shift accumulated in the amplifier, could have facilitated the high pulse quality. To the best of our knowledge, this is the shortest pulse duration from the Innoslab amplifiers at hundreds of watts average power in the millijoule energy regime.

Multi-millijoule class, high repetition rate, Yb:CALYO regenerative amplifier with sub-130 fs pulses

We demonstrate a high-energy, 1 kilohertz, Yb-based, femtosecond regenerative amplifier in a chirped pulse amplification (CPA) architecture by using a single disordered Yb:CALYO crystal, providing 125 fs pulses of 2.3 mJ energy per pulse at a central wavelength of 1039 nm. The amplified compressed pulses, with a spectral bandwidth of 13.6 nm, represent the shortest ultrafast pulse duration reported to date for any multi-millijoule class,Yb-crystalline classical CPA system without additional spectral broadening techniques. We have demonstrated an increase in the gain bandwidth proportionally to the ratio of the excited to total Yb³⁺ ion densities. A net wider spectrum of the amplified pulses is the result of the interplay between the increased gain bandwidth and the gain narrowing. Finally, our broadest amplified spectrum of 16.6 nm, corresponding to a 96 fs transform limited pulse, can be expanded further to support sub-100 fs pulse durations and 1-10 mJ energies at 1 kHz.

High-power femtosecond regenerative amplifier based on Yb:CaYAlO4 dual-crystal configuration

A thermal lens insensitive regenerative amplifier (RA) with a dual Yb:CaYAlO₄ (Yb:CYA) crystal configuration for extending gain spectra is demonstrated for the first time, to the best of our knowledge. By orthogonalizing the orientation of two a-cut Yb:CYA crystals in one RA, the Q switched spectrum with a full width at half maximum of 15.4 nm is generated, which is 1.5 and 1.6 times of the Q switched spectral bandwidth with π- and σ-polarization, respectively. With chirped pulses injection, this RA can deliver laser pulses with an average power exceeding 10 W at the repetition rate of 20-800 kHz and pulse energy of 1.5 mJ at 1 kHz. This is the highest average power from the Yb:CYA RA to the best of our knowledge. Finally, compressed pulses of 163 fs with 92% overall efficiency are realized. Thanks to the heat insensitive cavity design and excellent thermodynamic properties of the Yb:CYA crystal, the output laser beam is close to the diffraction limit with an M² value of 1.07 × 1.07.

High-power Yb:CALGO regenerative amplifier and 30 fs output via multi-plate compression

The pulse energy and average power are two long-sought parameters of femtosecond lasers. In the fields of nonlinear-optics and strong-field physics, they respectively play the role to unlock the various nonlinear processes and provide enough photon fluxes. In this paper, a high-energy and high-power Yb:CALGO regenerative amplifier with 120 fs pulse width is reported. This high-performance regenerative amplifier can work with high stability in a large tuning range of repetition rates. Varying the repetition rate from 3 to 180 kHz, the maximum output power of 36 W and the pulse energy up to 4.3 mJ, corresponding to a peak power of more than 20 GW are demonstrated. The output beam is near diffraction limited with M²= 1.09 and 1.14 on the horizontal and vertical directions, respectively. In addition, multi-plate compression is employed to achieve 30 fs output with 23 W average power which is attractive for applications such as high-harmonic generation.

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.

Compact millijoule Yb3+:CaF2 laser with 162 fs pulses

We report on a compact diode-pumped, chirped pulse regenerative amplifier system with a pulse duration of 162 fs and an output pulse energy of 1 mJ before as well as 910 µJ after compression optimized for the probing of ultrafast relativistic laser-plasma processes. A chirped volume Bragg grating (CVBG) acts as a combined pulse stretcher/compressor representing a robust solution for a CPA laser system in the millijoule range. Yb³⁺:CaF₂ is used as gain medium to support a large bandwidth of 16 nm (FWHM) when spectral gain shaping is applied. Chirped mirrors compensate for any additional dispersion introduced to the system.

Yb3+:LuAlO3 crystal as a gain medium for efficient broadband chirped pulse regenerative amplification

The experimental study results of a chirped pulse amplification regime are reported for the Yb:LuAlO₃ crystal with different polarization states in the gain media for the first time, to the best of our knowledge. Maximum output power of 5 W with 565 fs pulse duration was obtained for E//b-polarization at a 200 kHz repetition rate seeded by a 98 fs Yb:KYW oscillator. 165 fs pulses with output power of 4.5 W were demonstrated for E//c-polarized light in the crystal.

Direct regenerative amplification of femtosecond pulses to the multimillijoule level

We present a compact femtosecond nonlinear Yb:YAG thin-disk regenerative amplifier delivering pulses carried at a wavelength of 1030 nm with an average power of >200  W at a repetition rate of 100 kHz and an energy noise value of 0.46% (rms) in a beam with a propagation factor of M²<1.4. The amplifier is seeded with bandwidth-limited subpicosecond pulses without temporal stretching. We give estimates for the nonlinear parameters influencing the system and show that chirped mirrors compress the 2 mJ pulses to a near-bandwidth-limited duration of 210 fs.

Yb3+:CaYAlO4-based chirped pulse regenerative amplifier

The results of an experimental study of the chirped pulse amplification regime are reported for the Yb:CaYAlO₄ crystal with different polarization states in the gain media for the first time, to the best of our knowledge. A maximum output power of 4.2 W with 310 fs pulse duration was obtained for σ-polarization at 200 kHz repetition rate seeded by a 85 fs Yb:KYW oscillator. 215 fs pulses with an output power of 3 W and 190 fs with 2.3 W output power were demonstrated for π-polarized light in the crystal. Gain narrowing effects for different polarization states in the crystal are discussed.

Simple Yb:YAG femtosecond booster amplifier using divided-pulse amplification

A hybrid-system approach using a low-gain Yb:YAG single crystal booster amplifier behind a state-of-the-art industrial high-power femtosecond fiber system is studied to significantly increase the output pulse energy of the fiber amplifier. With this system, more than 60 W of average power is demonstrated at 100 kHz for pulse duration of 400 fs, corresponding to an energy per pulse of 600 µJ. Reducing the repetition rate, the energy is increased up to 2.5 mJ (before compression), which corresponds to the limitation due to laser damage threshold of the optical coatings. To scale further the energy, passive divided-pulse amplification is then implemented at the entrance of the bulk amplifier. Using this geometry, a safe nominal operating point is presented with output pulse energies of 3 mJ before and 2.3 mJ after compression and with a pulse duration of 520 fs, corresponding to a peak power of 4.4 GW.

200 kHz 5.5 W Yb(3+): YVO4-based chirped-pulse regenerative amplifier

A chirped-pulse regenerative amplifier based on a Yb:YVO4 (Yb:YVO) crystal was demonstrated for the first time, to our knowledge. A novel wavelength-independent off-axis technique was used to deliver 26.6 W of pump power with a low quantum defect. It was seeded by means of a 120 fs Yb:YVO4 oscillator. It generates as much as 5.5 W of average output power with chirped pulses and 4.2 W with 200 fs compressed pulses at a 200 kHz repetition rate. A maximum pulse energy of 140 μJ was obtained at pulse repetition frequencies up to 25 kHz at the central wavelength of 1018 nm.

Sub-50-fs widely tunable Yb:CaYAlO(4) laser pumped by 400-mW single-mode fiber-coupled laser diode

Yb:CaYAlO(4) has been investigated spectroscopically and compared to better known Yb:CaGdAlO(4). It turns out that both materials show very similar spectroscopic parameters relevant to ultrafast lasers design. Employing single-mode fiber-coupled 400-mW laser diode at 976 nm we measured pulses as short as 43 fs, and broad tunability of 40 nm with a simple single-prism setup.

High pulse energy multiwatt Yb:CaAlGdO4 and Yb:CaF2 regenerative amplifiers

We investigated and compared Yb:CaAlGdO4 and Yb:CaF2 regenerative amplifiers at repetition rates 5-10 kHz, a frequency range interesting for industrial applications requiring relatively high pulse energy. Both materials allow for pulse energies close to 1 mJ with sub-400-fs pulses. The two laser materials offer comparable performance in the pump power range investigated. The same regenerative amplifiers can be run up to 500 kHz for much faster material processing, with maximum output power of up to 9.4 W.

Generation of 150-fs pulses from a diode-pumped Yb:KYW nonlinear regenerative amplifier

Generation of sub-150-fs-level pulses has been obtained from an Yb-doped crystal-based regenerative amplifier by applying an innovative amplification scheme. This scheme is based on optimization of the linear and non-linear phase during the amplification process inside the regenerative amplifier cavity. This technique with Yb:KYW allows to achieve pulse durations from diode-pumped Yb-doped regenerative amplifiers that were up to now only accessible with more complex Ti:sapphire amplifiers. With this Yb-doped tungstate crystal used in regenerative amplifiers, 145 fs pulses centered at 1026 nm with a spectral bandwidth of 14 nm at 50 kHz for an average power of 1.6 W have been generated.