2019, Zhao, Yongguang, Chen, Weidong, Wang, Li, Wang, Yicheng, Pan, Zhongben, Dai, Xiaojun, Yuan, Hualei, Cai, Huaqiang, Zhang, Yan, Bae, Ji Eun, Park, Tae Gwan, Rotermund, Fabian, Loiko, Pavel, Serres, Josep Maria, Mateos, Xavier, Shen, Deyuan, Griebner, Uwe, Petrov, Valentin

Bilayer graphene synthesized by chemical vapor deposition is successfully applied as a saturable absorber (SA) for the passive mode-locking of a Tm,Ho:CLNGG laser at 2093nm. Near transform-limited pulses as short as 70 fs, i.e., 10 optical cycles, are produced at a 89 MHz repetition rate with 69 mW average output power. To the best of our knowledge, these are the shortest pulses ever reported from graphene-SA mode-locked Tm, or Ho-lasers in the 2 µm spectral region, including bulk and fiber lasers.

2021, Wang, Li, Chen, Weidong, Pan, Zhongben, Loiko, Pavel, Bae, Ji Eun, Rotermund, Fabian, Mateos, Xavier, Griebner, Uwe, Petrov, Valentin

We report on the first sub-100 fs mode-locked laser operation of a Tm3+-doped disordered calcium lithium tantalum gallium garnet (Tm:CLTGG) crystal. Soliton mode-locking was initiated and stabilized by a transmission-type single-walled carbon nanotube saturable absorber. Pulses as short as 69 fs were achieved at a central wavelength of 2010.4 nm with an average power of 28 mW at a pulse repetition rate of ∼87.7 MHz. In the sub-100 fs regime, the maximum average output power amounted to 103 mW.

2021, Alles, Adrian, Pan, Zhongben, Loiko, Pavel, Serres, Josep Maria, Slimi, Sami, Yingming, Shawuti, Tang, Kaiyang, Wang, Yicheng, Zhao, Yongguang, Dunina, Elena, Kornienko, Alexey, Camy, Patrice, Chen, Weidong, Wang, Li, Griebner, Uwe, Petrov, Valentin, Solé, Rosa Maria, Aguiló, Magdalena, Díaz, Francesc, Mateos, Xavier

We report on the development of a novel laser crystal with broadband emission properties at ∼2 µm – a Tm3+,Li+-codoped calcium tantalum gallium garnet (Tm:CLTGG). The crystal is grown by the Czochralski method. Its structure (cubic, sp. gr. 𝐼𝑎3¯𝑑, a = 12.5158(0) Å) is refined by the Rietveld method. Tm:CLTGG exhibits a relatively high thermal conductivity of 4.33 Wm-1K-1. Raman spectroscopy confirms a weak concentration of vacancies due to the charge compensation provided by Li+ codoping. The transition probabilities of Tm3+ ions are determined using the modified Judd-Ofelt theory yielding the intensity parameters Ω2 = 5.185, Ω4 = 0.650, Ω6 = 1.068 [10−20 cm2] and α = 0.171 [10−4 cm]. The crystal-field splitting of the Tm3+ multiplets is revealed at 10 K. The first diode-pumped Tm:CLTGG laser generates 1.08 W at ∼2 µm with a slope efficiency of 23.8%. The Tm3+ ions in CLTGG exhibit significant inhomogeneous spectral broadening due to the structure disorder (a random distribution of Ta5+ and Ga3+ cations over octahedral and tetrahedral lattice sites) leading to smooth and broad gain profiles (bandwidth: 130 nm) extending well above 2 µm and rendering Tm:CLTGG suitable for femtosecond pulse generation.