Continuous-wave Laser Operation Research Articles

Spectroscopy and diode-pumped laser operation of Pr:LaMgAl11O19 crystal

We report on the growth, spectroscopic properties and visible laser operation of Pr3+-doped LaMgAl11O19 (LMA) crystal. The absorption and emission spectra were recorded in visible wavelength range and the decay time of 3P0 manifold was measured to be about 34.5 μs at room temperature. Using an InGaN laser diode as pump source, continuous-wave laser operation of Pr:LMA crystal have also been demonstrated in red at about 645 nm and deep red at about 725 nm, which provide new linearly polarized sources for various potential applications.

Demonstration of Diode-Pumped Yb:LaF3 and Tm,Ho:LaF3 Lasers

Diode-pumped solid-state lasers using novel Yb:LaF3 and Tm,Ho:LaF3 crystals as laser gain materials are demonstrated herein. The Yb:LaF3 and Tm,Ho:LaF3 crystals were grown using the Bridgman method. By matching their absorption bands, continuous-wave laser operations were achieved for the first time. The Yb:LaF3 laser obtained a maximum average output power of 1.19 W with dual wavelengths of 1028 nm and 1033 nm. The maximum average output power and slope efficiency of the Tm,Ho:LaF3 laser were 574 mW and 18.5%, respectively. The Tm,Ho:LaF3 laser exhibited two peaks at 2043 nm and 2048 nm. Both the Yb:LaF3 and Tm,Ho:LaF3 crystals were confirmed to be laser gain materials.

Spectral properties and highly efficient continuous-wave laser operation in Nd, Gd:CaF2 crystals

Spectral properties of Nd, Gd:CaF2 crystals were investigated. In comparison with Nd:CaF2, the spectral parameters of Nd, Gd:CaF2 were altered in a large scale. LD-pumped true CW laser has been demonstrated in the crystals. The slope efficiency with the value of 45% in 0.5 at.% Nd, 5 at.% Gd:CaF2 was achieved, it is the highest slope efficiency in Nd doped CaF2 single crystals by LD-pumping. The system is a promising candidate for highly efficient lasers.

Laser Operation in a Tm:LuAG Crystal Grown by the Micro-Pulling-Down Technique

We report on the growth and laser operation of Tm:Lu3Al5O12 (Tm:LuAG) single crystal grown via the micro-pulling-down ( $\mu $ -PD) method, for the first time to the best of our knowledge. Spectral properties (absorption and fluorescence) and fluorescence lifetime of the Tm:LuAG crystal were measured at room temperature. Using a 790-nm diode laser as pump source, continuous-wave laser operation of the Tm:LuAG crystal was demonstrated with a maximum output power of 2.88 W and a slope efficiency of about 39.1% at 2016 nm. Passively $Q$ -switched laser operation was also investigated using Cr:ZnSe as saturable absorber. The maximum average output power reached about 0.53 W with the shortest pulse width of 54.3 ns and a pulse energy of $21.9~\mu \text{J}$ . This letter reveals that the $\mu $ -PD technique is reliable for growing high-performance Tm3+-doped crystals for various potential applications.

Effect of La3+ proportion on spectroscopic and continuous wave laser properties of Nd,La:CaF2 single crystals

The effect of the lanthanum proportion on the spectroscopic properties of Nd, La:CaF2 crystals was investigated. Compared with 0.5 at.% Nd:CaF2, the spectral parameters of 0.5 at.% Nd, x at.% La:CaF2 (x = 2, 5, 8) were altered in a large scale. Under laser diode pumping, the continuous-wave laser operations around 1.06 µm were demonstrated in the 0.5 at.% Nd, x at.% La:CaF2 (x = 2, 5, 8) samples. The 0.5 at.% Nd, 5 at.% La:CaF2 sample had the best laser performance with a maximum output power of 1.33 W and a slop efficiency of 40.3%.

Growth, spectral properties, and diode-pumped laser operation of a Nd3+-doped LaMgAl11O19 crystal.

A Nd3+-doped LaMgAl11O19 (Nd:LMA) crystal was grown by the Czochralski method. Room temperature polarized absorption spectra, fluorescence spectra, and fluorescence lifetime of the Nd:LMA crystal were measured and analyzed. The Judd-Ofelt parameters Ω2,4,6 were calculated to be 1.21×10-20, 3.63×10-20, and 2.35×10-20 cm2, respectively. The absorption and emission cross sections were calculated. Using a 790-nm diode laser as pump source, continuous-wave laser operation of an a-cut Nd:LMA crystal has been demonstrated with a maximum output power of 1.71W and slope efficiency of 40.4% for a 1055nm laser. Low-gain laser operation at 1082nm is also realized with a maximum output power of 1.46W and slope efficiency of 34.5%.

11 W continuous-wave laser operation at 209 μm in Tm:Lu16Sc04O3mixed sesquioxide ceramics pumped by a 796 nm laser diode

High quality thulium doped Lu1.6Sc0.4O3 mixed sesquioxide laser ceramics were fabricated using a solid-state reactive sintering method. Optical and spectroscopic properties of the ceramics were studied. A high transmittance almost identical to the theoretical value of the ceramics was reached at the lasing wavelength. A large Stark splitting of 920 cm−1 for the ground states 3H6 and 472 cm−1 for the first excited states 3F4 of Tm3+ were observed, resulting in a long wavelength emission band around 2.09 μm with low reabsorption losses at this wavelength. CW laser operation at 2.09 μm pumped by a 796 nm laser diode was achieved with an output power of 11 W and an optical-to-optical conversion efficiency of 28.9%, both of which are the highest values reported so far for lasing around 2.1 μm in Tm3+ doped mixed sesquioxide ceramics.

Highly efficient CW operation of a diode pumped Nd:Y2O3 ceramic laser

High efficiency continuous-wave laser operation of an in-house made Nd:Y2O3 ceramic was demonstrated. The Nd:Y2O3 laser ceramic was fabricated by vacuum sintering plus the hot isostatic pressing process, whose in-line transmittance reaches 81.6% at the wavelength of 1000 nm. The 1.08 and 1.36 µm CW laser oscillation of an uncoated ceramic sample was experimentally investigated. Both achieved the highest slope efficiency and output power so far reported for the Nd:Y2O3 ceramic lasers. For the operation of 4F3/2-4I11/2 transitions, simultaneous oscillations at 1074.6 nm and 1078.8 nm were observed. At an absorbed pump power of 7.0 W, a maximum output power of 3.01 W was obtained with a slope efficiency of 49.6%. For the laser operation of 4F3/2-4I13/2 transitions, a 1.68 W single wavelength at 1357.7 nm with the slope efficiency of 29.3% was achieved at the absorbed pump power of 6.7 W.

Widely tunable dual-wavelength operation of Tm:YLF, Tm:LuAG, and Tm:YAG lasers using off-surface optic axis birefringent filters.

In this work, we have demonstrated dual-wavelength continuous-wave laser operation in diode-end-pumped Tm:YLF, Tm:LuAG, and Tm:YAG lasers. A 3-mm-thick quartz birefringent filter with an optical axis 45° to the surface plane was exploited for achieving broadly tunable two-color laser operation. By using the different orders of the filter with varying filter width and free spectral range values, dual-wavelength operation has been achieved in 11, 12, and 8 different wavelength pairs in Tm:YLF, Tm:LuAG, and Tm:YAG, respectively. Fine tuning of the rotation angle of the birefringent filter enabled control of laser power in each line. To our knowledge, this is the first report of multicolor laser operation in these gain media, and the technique used is applicable to other laser operation regimes including mode-locking.

Experimental Investigation of Mid-Infrared Laser Action From Dy3+ Doped Fluorozirconate Fiber

Efficient continuous-wave laser operation at 2.982 $\mu \text{m}$ is achieved with a Dy3+:fluoride fiber pumped using an inhouse-built 1.1 $\mu \text{m}$ ytterbium (III) fiber laser. The laser output power reached is 554 mW, with a maximum slope efficiency of 18% with respect to the launched pump power. Additionally, the measured spontaneous luminescence within the visible wavelength range, under 1.1 $\mu \text{m}$ pumping, is presented and attributed to excited state absorption (ESA). The influence of the ESA on the laser performance is discussed. The results confirm that high output powers from Dy:fluoride fiber laser pumped at 1.1 $\mu \text{m}$ are possible.

Spectroscopic properties and continuous-wave deep-red laser operation of Eu3+-doped LiYF4.

Eu3+-doped LiYF4 is reexamined as a laser material for the visible spectral region. Polarized absorption and emission cross sections as well as the fluorescence lifetime are determined. Branching ratios and radiative lifetime are calculated within the theory of 4f-4f transition intensities, which takes into account the influence of an excited configuration of the opposite parity 4fN-15d. Continuous-wave laser operation at 702nm is demonstrated with a maximum output power of 15mW and a slope efficiency of 4.6% under pumping with a frequency-doubled Ti:sapphire laser at 393.5nm.

Highly efficient continuous-wave laser operation of LD-pumped Nd,Gd:CaF2 and Nd,Y:CaF2 crystals

Spectroscopic properties of Nd:CaF2 crystals are investigated. The photoluminescence intensity in the near infrared region is drastically enhanced by co-doping Gd3+ ions and Y3+ in Nd:CaF2 crystals. Preliminary laser experiments are carried out with 0.3%Nd,5%Gd:CaF2 and 0.3%Nd,5%Y:CaF2 crystals under laser diode pumping; true continuous wave laser operation is achieved with slope efficiencies of 42% and 39%, respectively, and the maximum output power reaches 1.188 W.

Growth, spectroscopy and continuous-wave laser performance of Nd3+:LiLu0.65Y0.35F4 crystal

A mixed fluoride crystal of LiLu0.65Y0.35F4 doped with Nd3+ ions was grown by the Bridgman–Stockbarger method. Polarized absorption and luminescence spectra as well as luminescence lifetime were measured at room temperature. Emission probabilities, branching ratios and radiative lifetime were studied within the Judd–Ofelt theory and the emission cross section spectra were calculated. Efficient continuous wave laser operation was demonstrated with the crystal. A maximum output power of 7.7 W and slope efficiency of 60% were achieved at 1047 nm for the TEM00 mode.

Highly-efficient mid-infrared CW laser operation in a lightly-doped 3 at.% Er:SrF2 single crystal.

3 at.% Er:SrF2 laser crystals with high optical quality were successfully grown using the temperature gradient technique (TGT). The intense mid-infrared emission was observed around 2.7 μm with excitation by a 970 nm LD. Based on the Judd-Ofelt theory, the emission cross-sections of the 4I13/2-4I11/2 transition were calculated by using the Fuchtbauer-Ladenburg (FL) method. Efficient continuous-wave laser operation at 2.8 µm was achieved with the lightly-doped 3 at.% Er:SrF2 crystal pumped by a 970 nm laser diode. The laser output power reached up to 1.06 W with a maximum slope efficiency of 26%.

Continuous-wave and chemical vapor deposition graphene-based passively Q-switched Er:Y2O3 ceramic lasers at 2.7 μm.

We report on 976-nm diode-pumped Er:Y2O3 ceramic lasers in continuous-wave and passively Q-switched regimes. The maximum output power of continuous-wave laser operation is about 0.78W with slope efficiency of about 11.8% at 2.7μm. Passively Q-switched Er:Y2O3 ceramic laser operation with chemical vapor deposition (CVD) graphene as the saturable absorber is also demonstrated for the first time, to our knowledge. Using a monolayer CVD graphene, the achieved shortest pulse width is about 408ns, while the shortest pulse width reduces to about 296ns with pulse energy of 2.59μJ and peak power of 8.77W by using a three-layer CVD graphene. The results reveal that graphene is a very promising saturable absorber operating in the middle infrared spectral region.

Highly efficient CW laser operation in 4 at. % Tm3+ and 4 at. % Y3+ codoped CaF2 crystals

Tm:CaF2 and Tm,Y:CaF2 single crystals were prepared by the temperature gradient technique. The spectral properties of Tm,Y:CaF2 single crystals were investigated and compared with those of Tm:CaF2. It was demonstrated that codoping with Y3+ ions could efficiently improve the spectroscopic properties. Tm,Y:CaF2 crystals have larger absorption cross-sections at the pumping wavelength, larger mid-infrared stimulated emission cross-sections, and much longer fluorescence lifetimes of the upper laser level (Tm3+: H43 level) than Tm:CaF2 crystals. Continuous-wave (CW) lasers around 1.97 μm were demonstrated in 4.0 at. % Tm,4.0 at. % Y:CaF2 single crystals under 792 nm laser diode (LD) pumping. The best laser performance has been demonstrated with a low threshold of 0.368 W, a high slope efficiency of 54.8%, and a maximum output power of 1.013 W.

Continuous-wave laser operation at 743 and 753 nm based on a diode-pumped c-cut Pr:YAlO3 crystal

We report on blue-diode-pumped continuous-wave Pr:YAlO3 (YAP) crystal lasers. Using a b-cut sample, a maximum output power of 181 mW is achieved at ∼747 nm with slope efficiency of 12.7% with respect to the absorbed power. Using a c-cut sample, a dual-wavelength laser at ∼743 and ∼753 nm is obtained with a total maximum output power of 72 mW by using the blue diode pumping, for the first time to our knowledge. These laser emissions are all linearly polarized and M2 factors of these output laser beams are also measured. YAP is experimentally verified to be one of effective oxide hosts for Pr-doped visible laser operation besides its fluoride counterparts.

High-Power CW and Q-Switched Tm:CaYAlO4 Lasers at $1.94~\mu \text{m}$ for Shallow Water Absorption

We report on 790-nm diode-pumped continuous-wave and passively Q-switched Tm:CYA lasers. For continuous-wave laser operation, a maximum output power of 7.62 W is achieved with slope efficiency of 50.9%. Passive Q-switching of the Tm:CYA crystal is also obtained with a maximum average output power of 1.32 W using a Cr:ZnSe saturable absorber. The shortest pulse width is about 42.6 ns with a pulse energy of 60.2 $\mu \text{J}$ and a pulse peak power of 1.41 kW. These results represent the best laser performances of continuous-wave and passively Q-switched Tm:CYA lasers, to date. The 1.94- $\mu \text{m}$ Tm:CYA lasers provide better laser sources for shallow absorption of biological tissue.

Femtosecond-laser-written hexagonal cladding waveguide in Tm:KLu(WO_4)_2: µ-Raman study and laser operation

We report on the fabrication, µ-Raman characterization, and continuous-wave laser operation of a channel waveguide with a hexagonal optical-lattice-like cladding fabricated in monoclinic Tm:KLu(WO4)2 crystal by femtosecond direct laser writing. µ-Raman spectroscopy indicates preservation of the crystalline quality in the core region and an anisotropic residual stress field. When pumped by a Ti:Sapphire laser at 802 nm, the Tm:KLu(WO4)2 buried channel waveguide laser generated 136 mW at 1843.7 nm with a slope efficiency of 34.2% and a threshold as low as 21 mW, which are the record characteristics for femtosecond-laser-written Tm crystalline waveguide lasers. The variation of the output coupling resulted in discrete wavelength tuning of the laser emission from 1785 to 1862 nm. The propagation losses in the waveguide are ~1.2 ± 0.3 dB/cm.

Efficient 1620 nm continuous-wave laser operation of Czochralski grown Er:Yb:Lu2Si2O7 crystal.

Efficient continuous-wave diode-pumped laser operation of Czochralski grown Er:Yb:Lu2Si2O7 crystal is reported. Polarized absorption and emission spectra, fluorescence lifetimes, and energy transfer efficiency from Yb3+ to Er3+ were determined. A maximal output power of 522 mW was achieved at 1620 nm with slope efficiency of 15.8% and absorbed pump threshold of 470 mW. Among the Er3+ and Yb3+ co-doped materials with long fluorescence lifetimes of the upper level 4I13/2, which are candidates for gain media of pulsed laser around 1.55 μm with high energy, comprehensive performance of the Er:Yb:Lu2Si2O7 crystal is the best till now.