2-μm wavelength, high-energy Ho:YLF chirped-pulse amplifier for mid-infrared OPCPA

Abstract

A 2-μm wavelength laser delivering up to 39-mJ energy, ∼10 ps duration pulses at 100-Hz repetition rate is reported. The system relies on chirped pulse amplification (CPA): a modelocked Er:Tm:Ho fiber-seeder is followed by a Ho:YLF-based regenerative amplifier and a cryogenically cooled Ho:YLF single pass amplifier. Stretching and compressing are performed with large aperture chirped volume Bragg gratings (CVBG). At a peak power of 3.3 GW, the stability was <1% rms over 1 h, confirming high suitability for OPCPA and extreme nonlinear optics applications. ultra-short mid-IR pulses, but further progress is hampered by the near exclusive usage of ∼1 μm pump lasers. These pump lasers impose an unfavorable photon ratio between pump and signal/idler that limits efficiency, prevents accessing the highly efficient class of non-oxide crystals, and presents serious power scaling limitations due to linear and two-photon absorption [12]. These limitations can be mitigated using powerful pump lasers emitting at 2-μm wavelength thereby reducing the photon ratio mismatch and allowing the use of highly nonlinear non-oxide crystals such as ZGP [13]. While the technology of such lasers, based on Q-switched Ho:YLF (or Ho:LuLiF) and Ho:YAG, is very mature for generating high-energy nanosecond pulses [14][15][16][17][18][19][20], amplification of few picosecond pulses from such systems to the multi-tens of mJ has not been reported. In this Letter, we report on a compact and stable laser system operating at 2-μm wavelength, delivering ∼10 ps duration optical pulses with up to 39-mJ output energy at 100-Hz repetition rate. Highly efficient temporal compression of narrow-band picosecond pulses was performed at the multi-tens of mJ energy-level in a chirped volume Bragg grating (CVBG).The laser system relies on chirped pulse amplification (CPA) architecture consisting of a fiber seeder, a CVBG stretcher, two consecutive amplification stages, and a large aperture CVBG compressor (Fig. 1). The all-fiber seeder is a multi-stage system (Menlo Systems GmbH) starting with an amplified modelocked Er:fiber oscillator delivering femtosecond optical pulses at 100-MHz repetition rate and 1.5-μm wavelength. These pulses are frequency shifted to 2052-nm wavelength and spectrally narrowed to ∼1.5 nm bandwidth before seeding a series of Tm:Ho fiber amplifiers [21]. The 4-nJ energy, picosecond duration pulses emerging from these amplifiers at 100 MHz form the seed for the CPA chain thereby removing the problem of modelocking Ho-based systems directly. These pulses are temporally stretched to 170-ps duration in a double-pass, CVBG-based stretcher. The CVBG (OptiGrate Corp.) used in this stretcher is broadband AR-coated around 2052 nm, has a 5 mm × 8 mm clear aperture, a chirp rate of 150 ps/nm, and a design wavelength of 2053.5 nm. Upon stretching, the 100-MHz train is passed through a rubidium titanyle phosphate (RTP) pulse picker to reduce the repetition rate to 100 Hz. The pulses are then passed through an optical isolator and directed toward a regen...

Generation of 3D ellipsoidal laser beams by means of a profiled volume chirped Bragg grating

“…Volume Bragg gratings, including CBG in photothermorefractive (PTR) glass [4], are widely used in different lasers thanks to their high diffraction efficiency, high damage threshold, and temperature and optical stability (see, e.g., [5][6][7] and references therein). The refractive index modulation period linearly changes along the direction of light propagation.…”

Study on laser characteristics of Ho:YLF regenerative amplifiers: Operation regimes, gain dynamics, and highly stable operation points

“…However, based on the observations and findings described in this paper, we propose the following physical interpretation. We observe that with a decrease in the Ho:YLF crystal temperature, the seed pulses experience a stronger amplification, caused by higher absorption cross sections at the pump wavelength and higher emission cross sections at the seed wavelength at lower temperatures [9,21]. Consequently, the HSPs (optimum gain depletion) is reached with fewer RTs and the pulses can be coupled out earlier.…”

“…RAs lasing at a wavelength of 2 μm and based, for example, on Ho:YLF, Ho:YAG [7], and Tm:YAP [8] have recently garnered attention as a viable driving source for mid-IR optical parametric amplifiers (OPAs) [9]. They can be used in conjunction with highly efficient non-oxide non-linear crystals (such as ZnGeP2 [9,10]), as opposed to the more conventional 1-μm pump sources.…”

“…They can be used in conjunction with highly efficient non-oxide non-linear crystals (such as ZnGeP2 [9,10]), as opposed to the more conventional 1-μm pump sources. Unfortunately, Ho:YLF RAs, with an upper state lifetime of about 15 ms (or equivalently, an inverse lifetime of ∼ 67 Hz), greatly suffer from the onset of bifurcation at the demonstrated repetition rates.…”

“…Unfortunately, Ho:YLF RAs, with an upper state lifetime of about 15 ms (or equivalently, an inverse lifetime of ∼ 67 Hz), greatly suffer from the onset of bifurcation at the demonstrated repetition rates. Typically, Ho:YLF RAs were either operated at relatively low repetition rates [9], thus completely suppressing the onset of bifurcation, at high repetition rates until the onset of bifurcation [11], or directly in the bifurcation at a stable double-pulsing state [12]. In the latter case, pulse-picking only the higher energy pulse at half the repetition rate allows the extraction of stable and high-energy pulses [12,13].…”