Highly efficient Er:YAP laser with 6.9 W of output power at 2920 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.

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.

Diode-pumped Tm:YAP laser operating at 2.3 µm with enhanced performance through cascade lasing

The laser diode (LD)-pumped Tm:YAP (a-cut, 3.5 at.%) laser generated a maximum ∼2.3 µm continuous wave (CW) laser output power of ∼3 W. The higher output power benefited from the positive effect of the cascade lasing (simultaneously operating on the 3H4 → 3H5 and 3F4 → 3H6 Tm3+ transition). It was the highest CW laser output power amongst the LD/Ti:Sapphire-CW-pumped ∼2.3 µm Tm3+-doped lasers reported so far. Under the cascade laser operation, the slope efficiency of the ∼2.3 µm laser emission versus the absorbed pump power increased from 13.0% to 21.4%.

976 nm and 808 nm dual-GSA-wavelength pumped 3 µm erbium-doped solid-state laser

A dual-wavelength pumping scheme at 976 nm and 808 nm is proposed to improve the performance of 3 µm Er:YAP laser. 976 nm and 808 nm correspond to the ground state absorption processes of 4I15/2→I11/2 and 4I15/2→I9/2, respectively. The experimental results indicate that the introduction of 808 nm pumping not only increases the total inversion population, but also can adjust the population distribution among the sublevels in the upper and lower manifold, thus supporting higher output power and multiple wavelengths emissions. Under the single-wavelength pumping, the maximum output powers of 1.192 W and 0.223 W are obtained for 976 nm and 808 nm pumping, respectively. With regard to the 976/808 nm dual-wavelength pumping, the achievable maximum output power is 1.398 W, increased by 17.3% compared to the case of single-wavelength pumping at 976 nm. The dual-wavelength pumped Er:YAP laser can also operate in a state of multi-wavelength emissions at 2.79 µm, 2.82 µm and 2.92 µm with different dual-wavelength pump power combinations. Considering the broadband absorption characteristics of ground state absorption and the convenience of obtaining near-infrared laser diodes pumping sources, the proposed dual-wavelength pump scheme shows great potential to realize high-power, high-efficiency 3 µm erbium-doped solid-state lasers with better cost-effectiveness and more compact structure.

Performance of the mid-infrared Q-switched LD side-pumped Er:YSGG MOPA laser

We report on a laser-diode (LD)-pumped master-oscillator power amplifier (MOPA) mid-infrared laser system based on an LD side-pumped Er:YSGG seed laser that can operate in both free-running and Q-switched regimes. In the free-running mode of the seed laser, the maximum amplified single-pulse energy was 83.4 mJ. In Q-switched mode of the seed laser, a maximum single-pulse energy of 7.8 mJ was achieved at 100 Hz repetition rate with the pulse width of 90 ns, corresponding to the peak power of 86.7 kW and the single-pass amplification factor of 1.66. The results indicate that the LD side-pumped MOPA structure is an effective way to realize a nanosecond ∼3µm mid-infrared laser with high repetition rate and high pulse energy.

Efficient continuous wave and passively Q switched Er:GdScO3 laser using Fe:ZnSe at 2.8 µm

We report on diode-pumped continuous wave and passively Q switched Er:GdScO₃ crystal lasers at around 2.8 µm. A continuous wave output power of 579 mW was obtained with a slope efficiency of 16.6%. Using Fe:ZnSe as a saturable absorber, a passively Q switched laser operation was realized. A maximum output power of 32 mW was generated with the shortest pulse duration of 286 ns at a repetition rate of 157.3 kHz, leading to a pulse energy of 204 nJ and a pulse peak power of 0.7 W.

Reduction of thermal effects in a 2.7-µm Er:Y2O3 ceramic laser with annular pumping

Reduction of thermal effects is a challenging aspect for power scaling of 2.7-µm bulk Er-lasers due to the large quantum defect when pumping at ∼ 0.97 µm. Here, we demonstrate that thermal effects in an Er:Y₂O₃ ceramic laser can be significantly reduced pumping by an annular beam, thus improving the continuous-wave (CW) laser performance in the 3-µm spectral range. The excitation conditions of the TEM₀₀ mode were determined theoretically by taking into account the propagation characteristics of the annular pump beam. For a comparison, the temperature and stress distributions are at first theoretically studied with three different pump configurations. In the experiment, output power of the Er:Y₂O₃ ceramic laser improved by ∼ 60% by changing the pump beam from coventional quasi-top-hat to a designed annular one. This work, as a proof-of-principle study, indicates the potential of power scaling of the 2.7-µm bulk Er-lasers pumping with an annular beam.

1.14 kW peak power mid-infrared Er:YAG planar waveguide MOPA laser

We report on a quasi-continuous Er:YAG planar waveguide laser operated at 2.94 µm based on the major oscillator power amplification configuration. With the total pump peak power of 32.01 kW, a maximum output peak power of 1.14 kW was obtained at the seed injection peak power of 184.4 W operated at 400µs, 40 Hz. Furthermore, the numerical simulation results indicate that better performance of the laser could be obtained with the higher injected seed laser power. To the best of our knowledge, this is the first experimental demonstration of 2.94 µm planar waveguide laser with an Er doped host material.

Tb,Y:SrF2 crystal for efficient laser operation in the visible spectral region

A Tb,Y:SrF₂ crystal with high optical quality is grown using the temperature gradient technique. The spectroscopic and laser properties of the crystal in the visible spectral region are studied. A fluorescence lifetime of 5.6 ms is measured from the crystal, which is beneficial for laser operation with a low threshold. A continuous-wave Tb,Y:SrF₂ laser delivers an output power of 259 mW at 545 nm, with a slope efficiency of 35.2%. To the best of the authors' knowledge, this is the first report on a Tb-doped SrF₂ laser and represents the highest output power for visible alkaline-earth fluoride lasers. The limitations for power scaling are discussed.

Efficient diode-pumped Er:YAP master-oscillator power-amplifier system for laser power improvement at 2920 nm

We report on the first demonstration of laser-diode-pumped master-oscillator power-amplifier (MOPA) system based on Er-doped bulk material working at 2920 nm. The relaxation oscillation at the beginning of the laser pulse from the Er:YAlO₃ (YAP) oscillator was suppressed effectively when the pump frequency was increased to 140 Hz, as a result of the establishment of a three-level system. In the amplifier, the small signal gain of the Er:YAP strongly depends on pump duration and repetition frequency, and can reach the upper limit of parasitic oscillation. Further, 25.5 mJ of output pulse energy has been achieved from the amplifier at 150 Hz frequency (2.2 ms pump duration), with over 32% of optical-to-optical efficiency. Further improvement of the amplification ability of the MOPA system was discussed.

13-W and 1000-Hz of a 2.7-µm laser on the 968 nm LD side-pumped Er:YAP crystal with concave end-faces

We demonstrate a 968-nm LD side-pumped Er:YAP laser with concave end-faces and a working frequency of 50∼1000 Hz. The maximum average powers of 26.75 and 13.18 W are obtained at 250 and 1000 Hz, corresponding to the slope efficiency of 16.2% and 9.0%, respectively. The M2 factors of 7.98 and 1.49 are determined under the multi-mode and single-mode, and three laser wavelengths of 2713, 2732 and 2796 nm are observed. The results indicate that the LD side-pumped Er:YAP crystal with negative curvature end-faces is a promising candidate for the high power and high frequency mid-infrared laser device.