Er3+:YLiF4 channeled waveguide laser near 2.7-2.8†µm fabricated by femtosecond laser inscription.

We report, for the first time to our knowledge, a demonstration of robust waveguide lasing near 2.7-2.8 µm in an erbium-doped fluoride host. Femtosecond laser inscription was employed to fabricate 50- and 70-µm diameter channeled waveguides inside an Er3+:YLiF4 crystal. The best power performance was obtained with the 70-µm diameter waveguide and 16% transmitting output coupler. The propagation loss and refractive index contrast were measured as 0.23 dB/cm and 7.1 × 10-4, respectively, for the 70-µm diameter waveguide. Both self-Q-switched (SQS) and continuous-wave (CW) operations could be obtained. During the SQS operation, as short as 240-ns pulses with average power of 51 mW, repetition rate of 368 kHz, and power slope efficiency of 15.2% were generated at the wavelength of 2717 nm with 465 mW of the pump power. During the CW operation, as high as 66 mW of output power was achieved at 2808 nm by using 460 mW of pump power at 798 nm, with a power slope efficiency of 19.6%.

Near-Infrared Triggered Degradation for Transient Electronics.

Electronics that disintegrate after stable operation present exciting opportunities for niche medical implant and consumer electronics applications. The disintegration of these devices can be initiated due to their medium conditions or triggered by external stimuli, which enables on-demand transition. An external stimulation method that can penetrate deep inside the body could revolutionize the use of transient electronics as implantable medical devices (IMDs), eliminating the need for secondary surgery to remove the IMDs. We report near-infrared (NIR) light-triggered transition of metastable cyclic poly(phthalaldehyde) (cPPA) polymers. The transition of the encapsulation layer is achieved through the conversion of NIR light to heat, facilitated by bioresorbable metals, such as molybdenum (Mo). We reported a rapid degradation of cPPA encapsulation layer about 1 min, and the rate of degradation can be controlled by laser power and exposure time. This study offers a new approach for light triggerable transient electronics for IMDs due to the deep penetration depth of NIR light through to organs and tissues.

Broadly tunable continuous wave 2.3-µm Tm3+:tellurite bulk glass laser.

We report, for the first time to the best of our knowledge, a continuous wave trivalent thulium ion (Tm3+)-doped bulk glass near 2.3 µm. In the experiments, a bulk Tm3+-doped tellurite glass with the stoichiometric composition of 74TeO2-12ZnO-4La2O3-10Na2O (Tm3+:TZLN) was used. Lasing operation was achieved by using an x-fold cavity at the free-running wavelength of 2303 nm. The maximum slope efficiency of 6.2% was obtained with respect to the absorbed pump power with a 1% transmitting output coupler. In this case, as high as 100-mW output power was generated with 2.2 W of absorbed pump power. Continuous, broad tuning was achieved from 2233 nm to 2400 nm. The excitation spectrum of the laser was also investigated and 2.3-µm lasing was obtained by varying the pump wavelength over the 773-809-nm range. The absorption cross section was determined to be 4.4 × 10-21 cm2, based on open-aperture z-scan measurement. By using the laser efficiency data, the emission cross section of the Tm3+:TZLN glass was further determined to be 1.3 × 10-20 cm2 at 2.3 µm.

Laser-micromachined zebra-patterned graphene as a mode locker with adjustable loss.

In this Letter, we describe a novel, to the best of our knowledge, device based on micro-structured graphene, referred to as zebra-patterned graphene saturable absorber (ZeGSA), which can be used as a saturable absorber with adjustable loss to initiate femtosecond pulse generation. Femtosecond laser micro-machining was employed to ablate monolayer graphene on an infrasil substrate in the form of stripes with a different duty cycle, resulting in the formation of regions with variable insertion loss in the 0.21%-3.12% range. The mode-locking performance of the device was successfully tested using a ${{\rm Cr}^{4 {+} }}{:}\,{\rm forsterite}$Cr4+:forsterite laser, operating near 1250 nm. In comparison with mode locking using non-ablated graphene, the ZeGSA device with regions of decreasing graphene, enabled improved power performance where the mode-locked output power increased from 68 mW to 114 mW, and the corresponding pulse duration decreased from 62 to 48 fs at the same incident pump power of 6.3 W. These experiments indicate that ZeGSA shows great potential as a laser mode locker with adjustable loss and that it should find applications in the development of femtosecond lasers over a broad spectral range.

Upconversion pumping of a 2.3 µm Tm3+:KY3F10 laser with a 1064 nm ytterbium fiber laser.

We report efficient lasing of the isotropic ${{\rm Tm}^{3 + }}\!:\!{{\rm KY}_3}{{\rm F}_{10}}$Tm3+:KY3F10 crystal near 2.3 µm via upconversion pumping with a 1064 nm ytterbium fiber laser as the pump source. When pumped at 1064 nm, an x-cavity ${{\rm Tm}^{3 + }}\!:\!{{\rm KY}_3}{{\rm F}_{10}}$Tm3+:KY3F10 laser operated at the free-running wavelength of 2344 nm. Lasing was obtained with output couplers having transmissions in the range of 1-3%, and as high as 124 mW of continuous-wave (cw) output power was generated with 604 mW of absorbed pump power by using the 3% output coupler. Broadly tunable cw lasing could be obtained in the 2268-2373 nm wavelength range. An analysis of the experimental power efficiency data shows that nearly all of the absorbed pump photons were converted to 2.3 µm laser output after accounting for the quantum defect of the laser transition and resonator losses. We expect that higher lasing efficiency should be possible by using longer crystals to increase the pump absorption.