A passively mode-locked, self-starting femtosecond Yb:KYW laser with a single highly dispersive semiconductor double-chirped mirror for dispersion compensation

Abstract

We demonstrate a semiconductor double-chirped mirror consisting of an AlAs/GaAs multilayer stack grown by molecular beam epitaxy. The mirror has a high negative group velocity dispersion of −2450 ± 100 fs2 and a reflectivity exceeding 98.9% over the spectral range spanning ±4 nm around 1035 nm. When used to compensate the cavity dispersion in a diode-pumped femtosecond Yb:KY(WO4)2 oscillator, at 490 mW of the absorbed pump power, the laser delivered 110 mW in pulses of 240 fs duration.

The crystal structure and luminescence quenching of poly- and single-crystalline KYW2O8:Tb3+

“…Furthermore, KYW 2 O 8 was studied with europium as a radiation converter in LEDs [10]. Especially for laser applications the yttrium site is partly replaced by ytterbium or erbium [11,12]. To our surprise, terbium was not studied in this host so far, even though it is an interesting candidate for efficient luminescence due to its small multi-phonon relaxation [13].…”

Optimization of broadband semiconductor chirped mirrors with genetic algorithm

“…In the first analytical approximation, the structure is far from optimized. The minimum GDD is not less than −2000 fs 2 , and the mirror fabricated according to this design would be inferior to our previous-manually tuned-structures [4,5]. For the genetic algorithm, the exact properties of this initial structure are unimportant for the final optimized mirror.…”

“…From all the optimized results, two mirror structures were selected and fabricated. Details of the epitaxial growth of the high-dispersion Bragg mirrors and their characterization may be found in [4,5,15]. The mirror structures were covered with a three-layer anti-reflective coating to avoid strong GDD oscillations, resulting from the intra-mirror cavity.…”

“…On the other hand, semiconductor chirped mirrors have lower refractive index contrast and, thus, require more DBR pairs, which allows to provide better separation of reflection of different wavelengths and makes it easier to tune constant negative GDD over a broader band. In our previous works [4][5][6] we have demonstrated tunable semiconductor double-chirped mirrors with negative dispersion for applications in femtosecond lasers operating near 1 µm. We have fabricated them using arsenide-based molecular beam epitaxy (MBE), and with intentionally introduced layer thickness spatial gradient, we were able to make the mirror properties (reflectivity and dispersion) tunable over an 80-nm range across the mirror surface.…”

Saturable absorber mirrors for ytterbium mode-locked femtosecond lasers

“…Dispersion management in Yb:KYW lasers, based on dispersive (chirped) mirrors has improved the lasers stability compared to the early prism-based designs. The cavity dispersion compensation with high negative group velocity dispersion (GVD) dielectric [6] or semiconductor [7] multilayer mirrors has been demonstrated, including the cavity with a single, extremely large negative GVD semiconductor reflector [8]. Saturable absorber mirrors (SAMs) supporting the Kerr effect mode-locking have further enhanced the stability and allowed for self-starting pulsed laser operation [9][10].…”