Sandrine Ricaud

On Yb:CaF2 and Yb:SrF2 : Review of spectroscopic and thermal properties and their impact on femtosecond and high power laser performance

We present an overview of laser results we obtained with Yb-doped calcium fluoride and its isotype strontium fluoride. In order to study the laser performance in femtosecond and high power regimes, spectral and thermal properties are first discussed including the potential of these crystals at room and cryogenic temperatures. Experimental demonstrations of high-power and ultrashort pulse oscillators and amplifiers are presented and analyzed.

Highly efficient, high-power, broadly tunable, cryogenically cooled and diode-pumped Yb:CaF2

We present a high-power diode-pumped Yb:CaF(2) laser operating at cryogenic temperature (77 K). A laser output power of 97 W at 1034 nm was extracted for a pump power of 245 W. The corresponding global extraction efficiency (versus absorbed pump power) is 65%. The laser small signal gain was found to be equal to 3.1. The laser wavelength could be tuned between 990 and 1052 nm with peaks that correspond well to the structure of the gain cross-section spectra registered at low temperature.

Short-pulse and high-repetition-rate diode-pumped Yb:CaF2 regenerative amplifier.

We present a diode-pumped regenerative amplifier based on an Yb:CaF(2) crystal optimized to produce short pulses for various repetition rates ranging from 100 Hz to 10 kHz. The shortest pulse duration generated is 178 fs, and the corresponding energy is 1.4 mJ before compression (620 microJ after), at a repetition rate of 500 Hz for 16 W of pump power. The bandwidth is 10 nm centered at 1040 nm. Higher repetition rate regimes have also been explored, allowing an optical-to-optical efficiency up to 10% at a high repetition rate.

Comparison of picosecond and femtosecond laser ablation for surface engraving of metals and semiconductors

In order to minimize thermal load to the workpiece pico- and femtosecond lasers gain an increasing market share in industrial applications such as surface structuring or thin film selective ablation. Due to nonlinear absorption they are capable to process any type of material (dielectrics, semiconductors, metals) and provide an outstanding quality suppressing heat affects on the workpiece. In this paper, we report on results about surface engraving of metals (Al, Cu, Mo, Ni), semiconductor (Si) and polymer (PC) using a picosecond thin disk Yb:YAG-amplifier, which could be used in the picosecond regime as well as in the femtosecond regime by simply changing the seed laser source. In the picosecond regime the oscillator pulses, ranging from 10 to 34ps, can be directly amplified which leads to a quite simple and efficient amplifier architecture. On the other hand, a broadband femtosecond oscillator and a CPA configuration can be used in order to obtain pulse duration down to 900fs. We compare these results to recently obtained achievements using commercial femtosecond lasers based on Yb-doped crystals and fibers and operating at comparable output power levels, up to 15Watt. Finally, we have considered etch rate and process efficiency for both ps- and fs-regimes as a function of average power, of fluence and of intensity.

High-power diode-pumped cryogenically cooled Yb:CaF2 laser with extremely low quantum defect

High-power diode-pumped laser operation at 992-993 nm under a pumping wavelength of 981 of 986 nm is demonstrated with Yb:CaF₂ operating at cryogenic temperature (77 K), leading to extremely low quantum defects of 1.2% and 0.7%, respectively. An average output power of 33 W has been produced with an optical efficiency of 35%. This represents, to the best of our knowledge, the best laser performance ever obtained at such low quantum defects on intense laser lines.

Ultrafast laser with high energy and high average power for industrial micromachining: Comparison ps-fs

Ultrafast lasers present a growing interest for industrial applications such as surface structuring or thin film selective ablation. Indeed, they combine the unique capacity to process any type of material, such as dielectrics, semiconductors or metals, with an outstanding precision and a reduced affected zone. In this paper, we report on results about surface engraving of metals (Al, Cu, Mo, Ni), semiconductor (Si) and polymer (PC) using a picosecond thin disk Yb:YAG-amplifier, which could be used in the picosecond regime as well as in the femtosecond regime by simply changing the seed laser source. In the picosecond regime the oscillator pulses (34ps) can be directly amplified which leads to a quite simple and efficient amplifier architecture. On the other hand, a broadband femtosecond oscillator and a CPA configuration can be used in order to obtain pulse duration down to 900fs. The results obtained with this thin disk laser are compared to ones achieved with two commercial femtosecond lasers respectively based on Yb-doped crystals and fibers, and operating at similar output power levels (up to 15Watt). Finally, we have considered etch rate and process efficiency for both ps-and fs-regimes as a function of average power, of fluence and of intensity.Ultrafast lasers present a growing interest for industrial applications such as surface structuring or thin film selective ablation. Indeed, they combine the unique capacity to process any type of material, such as dielectrics, semiconductors or metals, with an outstanding precision and a reduced affected zone. In this paper, we report on results about surface engraving of metals (Al, Cu, Mo, Ni), semiconductor (Si) and polymer (PC) using a picosecond thin disk Yb:YAG-amplifier, which could be used in the picosecond regime as well as in the femtosecond regime by simply changing the seed laser source. In the picosecond regime the oscillator pulses (34ps) can be directly amplified which leads to a quite simple and efficient amplifier architecture. On the other hand, a broadband femtosecond oscillator and a CPA configuration can be used in order to obtain pulse duration down to 900fs. The results obtained with this thin disk laser are compared to ones achieved with two commercial femtosecond lasers respectiv...

100-fs-level diode-pumped Yb-doped laser amplifiers

Ultrashort pulse lasers with pulse duration on the level of 100 fs can be used for à variety of interesting applications that rely on multiphoton processes or ultrafast dynamics. Up to now, this field was reserved to Ti:sapphire-based laser systems that exhibit a quite complex laser architecture and relatively low laser efficiency. This may be an important reason why such applications could not yet penetrate into large scale industrial applications. We have realized an Yb-doped tungstate-based regenerative amplifier in innovative amplifier architecture. We succeeded to produce 106-fs-pulses at 70μJ and 140 fs at 40 μJ pulse energy, respectively. The average power is on the level of several Watts. The optimized management and exploitation of dispersive and nonlinear effects during the amplification process inside the regenerative amplifier cavity enabled the generation of such short pulses with excellent temporal quality and in an extremely simple and robust laser architecture that is well suited for industrial environments. Applying the same amplifier architecture to an Yb:YAG thin disk regenerative amplifier enabled the generation of pulses as short as 360-fs at high pulse energies exceeding 200 μJ and high average powers of more than 30 W.

Kerr lens mode-locking of Yb:CaF2

Through high-brightness optical pumping with a fiber laser, we demonstrate a soft-aperture Kerr lens modelocked (KLM) operation in a Yb:CaF2 crystal. Stable 117 fs pulses are producing at an average power of 560 mW.

Direct amplification of ultrashort pulses in μ-pulling down Yb:YAG single crystal fibers

We demonstrated that Yb:YAG single crystal fibers have a strong potential for the amplification of femtosecond pulses. Seeded by 230 fs pulses with an average power of 400 mW, the system produced 330 fs pulses with an average power of 12 W. This is the shortest pulse duration ever produced by a Yb:YAG amplifier. The gain in the single crystal fiber reached a value as high as 30 in a simple double pass configuration.

Broadband Yb:CaF2 regenerative amplifier for millijoule range ultrashort pulse amplification

We report on a diode-pumped regenerative amplifier based on Yb:CaF2 material, delivering pulses up to 1.8mJ pulse energy at a repetition rate of 100Hz. The crystal is pumped at the zero line at 978 nm with a 10W continuous wave (CW) fiber coupled laser diode. The pulses have a spectral bandwidth of 16nm centered at 1040 nm, which indicates a good potential for millijoule range sub 100fs pulse duration after compression. It is also a good candidate for seeding higher energy diode-pumped ytterbium lasers.