28.02 W LD side-pumped CW laser operated at 2.8†µm in YSGG/Er:YSGG/YSGG crystal.

We demonstrated a 978 nm laser diode (LD) side-pumped YSGG/Er:YSGG/YSGG composite crystal with a size of Ф 3 mm × 65 mm and continuous-wave (CW) mode. By optimizing resonator length and output mirror transmittance, a maximum output power of 28.02 W is generated, corresponding to slope efficiency of 17.55% and optical-optical efficiency of 12.29%, respectively. The thermal focal lengths are obtained by resonator stability condition. The laser wavelength is centered near 2.8 µm. Moreover, the beam quality factors M x2/M y2 are fitted to be 8.14 and 7.35, respectively. The above results indicate that a high-performance 2.8 µm CW laser can be achieved by LD side-pumped YSGG/Er:YSGG/YSGG composite crystal with excellent heat dissipation ability, which promotes effectively the development and applications of the mid-infrared solid-state lasers.

Growth, spectroscopy and SESAM mode-locking of a "mixed" Yb:Ca(Gd,Y)AlO4 disordered crystal.

We present the growth, spectroscopy, continuous-wave (CW) and passively mode-locked (ML) operation of a novel "mixed" tetragonal calcium rare-earth aluminate crystal, Yb3+:Ca(Gd,Y)AlO4. The absorption, stimulated-emission, and gain cross-sections are derived for π and σ polarizations. The laser performance of a c-cut Yb:Ca(Gd,Y)AlO4 crystal is studied using a spatially single-mode, 976-nm fiber-coupled laser diode as a pump source. A maximum output power of 347 mW is obtained in the CW regime with a slope efficiency of 48.9%. The emission wavelength is continuously tunable across 90 nm (1010 - 1100 nm) using a quartz-based Lyot filter. With a commercial SEmiconductor Saturable Absorber Mirror to initiate and maintain ML operation, soliton pulses as short as 35 fs are generated at 1059.8 nm with an average output power of 51 mW at ∼65.95 MHz. The average output power can be scaled to 105 mW for slightly longer pulses of 42 fs at 1063.5 nm.

Polarization switching in a mid-infrared Er:YAlO3 laser.

We report on a polarization-resolved study of mid-infrared emission properties of Er3+-doped orthorhombic yttrium aluminum perovskite YAlO3 single crystal. For the 4I11/2 → 4I13/2 Er3+ transition, the stimulated emission cross section is 0.20 × 10-20 cm2 at 2919 nm for light polarization E ‖ c. Pumped by an Yb-fiber laser at 976 nm, the 10 at.% Er:YAlO3 laser delivered 1.36 W at 2919 nm with a slope efficiency of 31.4%, very close to the Stokes limit, a laser threshold as low as 33 mW and a linear polarization. Pump-induced polarization switching between E || b and E || c eigen states was observed and explained by excited-state absorption from the terminal laser level.

Spectral broadening of a mixed Nd: CYGA crystal with tunable laser operation beyond 1100†nm.

A broader emission band of the novel Nd: CaY0.9Gd0.1AlO4 (Nd: CYGA) mixed crystal was proved by the introduction of Gd3+ ions in Nd: CaYAlO4 (Nd: CYA) crystal, and a diode-pump tunable Nd: CYGA laser operation was achieved successfully. Due to the broad emission spectrum with the full width at half maximum (FWHM) of 23 nm, a tuning range of 32 nm from 1075 nm to 1107 nm was achieved, and the results were considered to be the first time for Nd-doped crystals to be tuned to such a long wavelength at 1107 nm, which promotes the further development of near-infrared tunable lasers. The maximum output power was 1.05 W at the center wavelength of 1081.4 nm, corresponding to the slope efficiency of 26.6%. Furthermore, we also demonstrated a continuous-wave 1105 nm laser with the output power of 53 mW. Our work indicates that Nd: CYGA crystal is a potential Nd-doped gain medium for generating all-solid-state near-infrared lasers.

Diode-pumped SESAM mode-locked Yb:(Y,Gd)AlO3 laser.

We report on the continuous-wave (CW) and mode-locked (ML) laser performance of an Yb3+-doped yttrium-gadolinium orthoaluminate crystal, Yb:(Y,Gd)AlO3. Pumping by a single-transverse-mode fiber-coupled 976 nm InGaAs laser diode, the maximum output power in the CW regime amounted to 429 mW at 1041.8 nm corresponding to a slope efficiency of 51.1% and a continuous wavelength tuning across 84 nm (1011-1095 nm) was achieved. The self-starting ML operation of the Yb:(Y,Gd)AlO3 laser was stabilized by a semiconductor saturable absorber mirror. Soliton pulses as short as 43 fs were generated at 1052.3 nm with an average output power of 103 mW and a pulse repetition rate of ∼70.8 MHz. To the best of our knowledge, our result represents the first report on the passively mode-locked operation of a Yb:(Y,Gd)AlO3 laser, and the shortest pulse duration ever achieved from any Yb3+-doped orthorhombic perovskite aluminate crystals.

Dual effects on Ho3+ ∼4.0 µm emission by Nd3+ ions in (Y,Gd)AlO3 crystal.

For the first time, to the best of our knowledge, the use of Nd3+ codoping for enhancing the ∼4.0 µm emission from the Ho3+:5I5 → 5I6 transition was investigated in a Ho3+, Nd3+-codoped Gd0.1Y0.9AlO3 [(Y,Gd)AlO3] crystal [Ho/Nd:(Y,Gd)AlO3]. In this study, the ∼4.0 µm emission characteristics and energy transfer were investigated in detail, and it was found that the codoped Nd3+ ions in the Ho/Nd:(Y,Gd)AlO3 crystal significantly enhanced the Ho3+:∼4.0 µm emission, depopulated the lower laser level of Ho3+:5I6, and had little effect on the higher laser level of Ho3+:5I5. It was also found that the energy transfer efficiency from Nd3+:4F3/2 to Ho3+:5I5 was as high as 43.0%, indicating that Nd3+ ions can be used as an effective sensitizer for Ho3+ ions and that Ho/Nd:(Y,Gd)AlO3 crystal has the potential to be pumped by a commercialized InGaAs laser diode (LD). These results suggest that Ho/Nd:(Y,Gd)AlO3 crystals are likely to become attractive hosts for developing solid-state lasers at around 4.0 µm under a conventional 808 nm LD pump.

Kerr-lens mode-locked ytterbium-activated orthoaluminate laser.

We report on the first, to the best of our knowledge, Kerr-lens mode-locked laser based on an Yb3+-doped perovskite-type orthoaluminate crystal exploiting two different principal light polarizations. The Yb:(Y,Gd)AlO3 laser delivers soliton pulses as short as 32 fs at 1067 nm with an average output power of 328 mW and a pulse repetition rate of ∼84.6 MHz for E || a polarization. For the orthogonal E || b polarization, 33-fs pulses are generated at 1057 nm with an average output power of 305 mW. Power scaling to a maximum average output power reaching 2.07 W is achieved at the expense of longer pulse duration (72 fs for E || b), corresponding to an optical efficiency of 43.9% and a peak power of 303 kW.

Intense 2.1-4.2 µm broadband emission of Co/Er:PbF2 mid-infrared laser crystal.

A novel mid-infrared (MIR) laser crystal Co/Er:PbF2 was successfully grown. The use of Er3+ ion co-doping to sensitize a Co2+ ion and enhance the 2.1-4.2 µm broadband MIR emission of the Co2+ ion in a PbF2 crystal was studied for the first time, to the best of our knowledge. The Er3+ ion was demonstrated to be an effective sensitizer of the Co2+ ion, making the Co/Er:PbF2 crystal propitious to be pumped by commercialized laser diodes. Furthermore, with Er3+ ion co-doping, the local symmetry of Co2+ and Er3+ ions was seriously distorted, thereby enhancing the 2.1-4.2 µm MIR emissions. This study provides a path for designing MIR laser materials with optimal performance.

Yb:GdScO3 crystal for efficient ultrashort pulse lasers.

We present, to the best of our knowledge, the first demonstration of thermal, optical, and laser properties of Yb:GdScO3 for potentially efficient ultrashort pulse lasers. The stimulated emission cross section at 1025 nm (E//c) is 0.46×10-20cm2 with the emission band width of 85 nm, even broader than the well-known Yb:CaGdAlO4. It has quite a high thermal conductivity of 5.54W/(m⋅K) at 50°C, comparable with Yb:YAG. In the continuous-wave regime, the maximum output power of 13.45 W at 1063.9 nm was generated with the optical-to-optical efficiency of 63.3%. These results suggest that the Yb:GdScO3 crystal is a promising candidate for ultrashort pulse lasers.

Efficient enhancement of bismuth near infrared luminescence by the co-doping of tantalum in GYAP crystal.

Bi/Ta double doped Gd0.1Y0.9AlO3 (Bi/Ta:GYAP) near-infrared (NIR) laser crystal was successfully grown. The codoping of Ta5+ was demonstrated to effectively enhance the NIR fluorescence emission in Bi/Ta:GYAP crystal for the first time. The introduced Ta5+ ion can induce the change of valence states from Bi3+ to Bi+ based on the charge compensation mechanism, bringing about the enhanced NIR fluorescence emission. The three NIR fluorescence emission peaks centering at 1005, 1195, and 1280 nm were ascribed to three different Bi+ active centers in Bi/Ta:GYAP crystal. These results suggest that the Bi/Ta:GYAP crystal may have potential applications in NIR broadband lasers.

Charge compensation effects of Yb3+ on the Bi+: near-infrared emission in PbF2 crystal.

The use of Yb3+ codoping for enhancing the near-infrared (NIR) emission in Bi, Yb codoped PbF2 crystal was investigated for the first time, to the best of our knowledge. The NIR and visible fluorescence emission properties of the as-grown crystals were investigated in detail. It was found that the Yb3+ ion can act as an effective charge compensated ion to bring about the conversion from Bi2+ to Bi+, enhancing the NIR fluorescence emission in Bi:PbF2 crystal. Moreover, the NIR fluorescence emission peaking at around 1090 and 1485 nm was demonstrated to be two different Bi+ related centers, Bi(I) and Bi(II), respectively. These results suggest that Bi, Yb codoped PbF2 crystal may become an attractive gain material for developing NIR broadband lasers under pumps of different wavelengths.

Passively Q-switched dual-wavelength green laser with an Yb:YAG/Cr4+:YAG/YAG composite crystal.

A compact dual-wavelength passively Q-switched green laser by intra-cavity frequency doubling of a Yb:YAG/Cr4+:YAG/YAG composite crystal was demonstrated for the first time to our best knowledge. The maximum green laser output power of 1.0 W was obtained under the pump power of 9.7 W, and the corresponding slope efficiency is 15.2%. The shortest pulse width, largest pulse energy, and highest peak power were achieved to be 5.54 ns, 246.1µJ, and 40.76 KW, respectively. Dual-wavelength laser oscillation simultaneously at 515 nm and 524.5 nm has been achieved. This passively Q-switched dual-wavelength green laser can be used as a laser source for Terahertz generation.

Directional release of the stored ultrashort light pulses from a tunable Bragg-grating microcavity.

We demonstrate numerically the ability for directionally releasing the stored ultrashort light pulse from a microcavity by means of two-pulse nonlinear interaction in a cascading Bragg grating structure. The setting is built by a chirped grating segment which is linked through a uniform segment, including a tunable microcavity located at the junction between the two components. Our simulations show that stable trapping of an ultrashort light pulse can be achieved in the setting. The stored light pulse in a microcavity can be possibly released, by nonlinearly interacting with the lateral incident control pulse. Importantly, by breaking the symmetry of potential cavity, the stably trapped light pulse can be successfully released from the microcavity to the expected direction. Owing to the induced optical nonlinearity, the released ultrashort light pulses could preserve their shapes, propagating in a form of Bragg grating solitons through the uniform component, which is in contrast to the extensively studied light pulse trappings in photonic crystal cavities which operate at the linear regime.

Sensitization and deactivation effects of Nd3+on the Ho3+ : 3.9 µm emission in a PbF2 crystal.

The use of Nd3+ codoping for sensitizing the Ho3+ ion and enhancing the ∼3.9 µm emission from Ho3+:I55→I65 was investigated in the PbF2 crystal for the first time, to the best of our knowledge. The ∼3.9 µm fluorescence emission properties and energy transfer mechanism of the as-grown crystals were investigated. The results show that the Nd3+ ion can act as a sensitizer to the Ho3+ ion, providing an efficient excitation channel, making the Ho3+/Nd3+:PbF2 crystal propitious to be pumped by commercialized InGaAs laser diodes (LDs). Moreover, an enhanced ∼3.9 µm emission was obtained in the Ho3+/Nd3+:PbF2 crystal due to the codoping of Nd3+ ions, leading to an efficient energy transfer from a lower laser level of Ho3+:I65 to Nd3+:I15/24, while having little influence on the higher laser level of Ho3+:I55. These advantageous spectroscopic characteristics indicate that the Ho3+/Nd3+:PbF2 crystal might have potential application in ∼3.9 µm mid-infrared lasers under a conventional 808 nm LD pump.

Diode-end-pumped Ho, Pr:LiLuF4 bulk laser at 2.95 µm.

A diode-end-pumped continuous-wave (CW) and passively Q-switched Ho, Pr:LiLuF4 (Ho, Pr:LLF) laser operation at 2.95 µm was demonstrated for the first time, to the best of our knowledge. The maximum CW output power was 172 mW. By using a monolayer graphene as the saturable absorber, the passively Q-switched operation was realized, in which regimes with the highest output power, the shortest pulse duration, and the maximum repetition rate were determined to be 88 mW, 937.5 ns, and 55.7 kHz, respectively. The laser beam quality factor M2 at the maximum CW output power were measured to be Mx2=1.48 and My2=1.47.

Enhanced 2.7 µm mid-infrared emissions of Er3+ via Pr3+ deactivation and Yb3+ sensitization in LiNbO3 crystal.

The use of Pr3+ codoping for enhancement of the transition of Er3+: 4I11/2 → 4I13/2 2.7 µm emissions was investigated in the Er/Yb codoped LiNbO3 crystal for the first time. It is found that the codoped of Pr3+ ion in Er3+, Yb3+ and Pr3+ triply doped LiNbO3 crystal (Er/Yb/Pr: LN) greatly enhances Er3+: 2.7 µm emission under excitation of a common 970 nm laser diode, depopulates the lower laser level of Er3+:4I13/2, and has little influence on the higher laser level of Er3+:4I11/2 at the same time for population inversion. The 2.7 µm emission characteristics and energy transfer were investigated in detail. The energy transition efficiency from lower laser level of Er3+:4I13/2 to Pr3+:3F4 level is as high as 0.42, indicating that the Pr3+ ion is an effective deactivation ion for Er3+ ion in LiNbO3 crystal. These results suggest that Er/Yb/Pr: LiNbO3 crystal may become an attractive host for developing solid state lasers at around 2.7 µm under a conventional 970 nm LD pump.

Enhanced emission of 2.86 µm from diode-pumped Ho(3+)/Yb(3+)-codoped PbF(2) crystal.

A novel Ho(3+)Yb(3+)-codoped PbF(2) mid-IR laser crystal was successfully grown and analyzed. Enhanced emission at 2.86 µm was observed from the crystal under excitation of a common 970 nm laser diode for the first time. The effect of Yb(3+) codoping on the 2.86 µm photoluminescence of Ho(3+) was investigated. In comparison to Ho(3+)-singly doped PbF(2) crystal, the Ho(3+)/Yb(3+)-codoped PbF(2) crystal possessed comparable quantum efficiency (88.8%), and fluorescence branching ratio (20.52%) along with a larger calculated emission cross section (1.90×10(-20) cm(2)) corresponding to the laser transition (5)I(6)→(5)I(7) of Ho(3+). It was found that the introduced Yb(3+) enhanced the 2.86 µm emission by depopulating the Ho(3+):(5)I(7) level. The energy transfer (ET) efficiency from Yb(3+):(2)F(5/2) to Ho(3+):(5)I(6) is as high as 96.7%, indicating that Yb(3+) ion is an effective sensitizer for Ho(3+) ion in PbF(2) crystal. These results suggest that Ho(3+)/Yb(3+)-codoped PbF(2) crystal may become an attractive host for developing solid state lasers at around 2.86 µm under a conventional 970 nm LD pump.

Intense 2.89 µm emission from Dy³âº/Yb³âº-codoped PbF2 crystal by 970 nm laser diode pumping.

A novel Dy(3+)/Yb(3+) co-doped PbF2 mid-IR laser crystal was successfully grown using the vertical Bridgman method. Efficient emission at around 3 µm from the crystal was observed under excitation of a conventional 970 nm laser diode (LD). The energy transfer efficiency from Yb(3+) to Dy(3+) in Dy(3+)/Yb(3+):PbF2 crystal is as high as (97.7±0.3)%. It is also found that the Dy(3+)/Yb(3+):PbF2 crystal possesses long fluorescence lifetime (15.4±0.2) ms, high quantum efficiency (95.0±0.3)%, and large emission cross section (1.37±0.11)×10(-20) cm2 corresponding to the stimulated emission of Dy(3+):(6)H(13/2)→(6)H(15/2) transition. Additionally, the phonon energy of the crystal was analyzed by the Raman spectrum. These results indicate that Dy(3+)/Yb(3+):PbF2 crystal may become a promising material for 3 µm solid state lasers under a conventional 970 nm LD pump.

Fabrication and characterization of cerium-doped terbium gallium garnet with high magneto-optical properties.

High optical quality (Tb((1-x))Ce(x))3Ga5O12 (TCGG) single crystal has been grown by the Czochralski method. The optical and magneto-optical properties of the TCGG are analyzed in detail and the Verdet constant (V) of TCGG is compared with that of undoped terbium gallium garnet (TGG) crystal. TCGG presents a very high transmittance, particularly in the visible-near infrared (VIS-NIR) region, and its V is obviously larger than that of TGG in the VIS-NIR region. The figure of merit and optical features point out the superior characteristics of TCGG with respect to TGG.

760 fs diode-pumped mode-locked laser with Yb:LuAG crystal at 1032 nm.

In this study, we experimentally demonstrate the generation of 760 fs pulse duration from a diode-pumped Yb:LuAG mode-locked laser at 1032 nm. At the repetition rate of 58.6 MHz, the maximum average power of 1.07 W was obtained, corresponding to the peak power of 24 kW. To our knowledge, these results represent the shortest pulse duration and highest peak power ever obtained for a 1032 nm mode-locked laser with Yb:LuAG crystal.