The discovery of two-dimensional (2D) material graphene has opened a door towards a class of layered novel nanomaterials with unique photonic and optoelectronic properties. Recently many new 2D ...materials have been reported, including topological insulators (TIs), transition metal dichalcogenides (TMDs) and black phosphorus (BP). These materials have been demonstrated high optical nonlinearity and Pauli blocking used as saturable absorbers (SAs) in pulsed lasers. In this paper, we summarize the current specifications from these 2D materials based mode-locked and Q-switched lasers. The laser performance in operating wavelength, optical bandwidth, repetition rate and pulse energy is reviewed. Finally future perspective is suggested.
•Mode-locked and Q-switched lasers based on three 2D materials are reviewed.•Best specifications of bandwidth, repetition rate and pulse energy are summarized.•Material basic properties, fabrication and characterization are also introduced.
--The role of injection seeding power on the operation and output characteristics of a single-longitudinal-mode (SLM) injection seeded Q-switched fiber laser is investigated. The mode coupling ...between seeding laser and the potential longitudinal-modes of the oscillator changes as the injection seeding power increase. So the Q-switched laser may operate at different regimes which can be distinguished by the pulse features. Only with a proper range of injection seeding power that is not too larger or too small, the operation of injection seeded Q-switched fiber laser with narrow-linewidth, high peak power and narrow pulsewidth laser pulses is possible. The Q-switched fiber laser linewidth is narrowed through inserting a dual-OCs oscillator into the laser cavity. 200-ns, 1-W peak power SLM Q-switched laser pulse with nearly transform-limited linewidth is obtained when the pump power is 300 mW.
The thermal effect and Q-switching of flashlamp-pumped Cr, Tm, Ho: YAG (CTH: YAG) laser were investigated systematically. The fraction of pump power dissipated as heat in flashlamp-pumped CTH: YAG ...laser system was evaluated for the first time by measurements and calculations on thermal lens effect. The quasi-steady state and transient temperature distributions of laser rod were numerical simulated. In addition, Electro-optically Q-switching was studied by design of thermal effect compensation resonator. An unusual phenomenon that the optimal delay time of Q-switch in CTH: YAG was shorter than the pump duration was reported for the first time as far as we know. According to the experimental and theoretical calculation results, the main cause of the phenomenon is the long lifetime of lower laser level, followed by up-conversion and fluorescence quenching at high temperature. The mechanism proposed in this paper is of great significance for the design of highly efficient Q-switched CTH: YAG lasers.
•The fraction of pump power dissipated as heat in flashlamp-pumped CTH: YAG was evaluated.•Transient temperature distributions of laser rod were numerical simulated.•The optimal delay time of Q-switch in CTH: YAG was found shorter than the pump duration.•The experimental results were explained through a modified rate equation system.
•Q-switch Ho:Sc2SiO5 laser modulated by a acousto-optic modulator and a Cr2+:ZnSe is reported for the first time.•The maximum peak power is obviously higher than the actively and passively Q-switch ...ones.•Ho:Sc2SiO5 possesses large energy splitting, wide absorption and emission spectrum.
A double Q-switch (DQS) Ho:Sc2SiO5 laser modulated by a acousto-optic modulators (AOM) combined with a Cr2+:ZnSe saturable absorber (SA) was reported for the first time. The actively Q-switch (AQS) and passively Q-switch (PQS) were also studied. For the DQS mode, a maximum average output power of 2.49W under the incident pump power of 12.5W was obtained, corresponding to a slope efficiency of 24%. The characteristics of the DQS Ho:SSO laser versus different repetition frequencies (RF) of the AOM were researched. The maximum single-pulse energy of the DQS Ho:SSO laser was calculated to 1.98mJ. The maximum peak power of the DQS Ho:SSO laser was 49.5kW. The output beam quality factor M2 of DQS Ho:SSO laser was measured to be 1.15 with the highest peak power by knife-edge method at different positions.
Selective frequency mixing in a cascaded Nd:YVO4 self-Raman laser was investigated for wavelength-switchable visible light output. Phase-matching with temperature tuning of both critical and ...non-critical phase-matched LBO crystals was analyzed. The critical phase-matched LBO crystal with θ = 86.0° and φ = 0° generated five discrete visible wavelengths by frequency mixing among the fundamental, first, and second Stokes waves, without sub-zero °C cooling. While laser performance examination was experimentally limited to frequency conversion of the first and second Stokes fields, average output power across three visible wavelengths was high, at 2.2, 1.31, and 1.58 W for 588, 620, and 657 nm, respectively, for the incident power of 15.5 W. This is promising for practical laser sources with multi-wavelength tunability across the visible spectrum. Such lasers can replace numerous single-line sources for various applications.
•Selective frequency mixing in a cascaded Nd:YVO4 self-Raman laser was investigated.•A diffusion-bonded crystal was used to reduce thermal lens effect and increase effective length of Raman gain medium.•Critical phase-matched LBO crystal realized the frequency doubling of second Stokes wave without sub-zero °C cooling.•Average output power of 2.2, 1.31, and 1.58 W was obtained for 588, 620, and 657 nm, respectively.•Such lasers can replace numerous single-line sources for various applications.
Background
Axillary hyperpigmentation (AH) is a condition in which axillary skin is darker than the adjacent areas. To date, there is no standard treatment for AH. The Q‐switched neodymium‐doped ...yttrium aluminum garnet 1064‐nm(QS) laser and intense pulsed light (IPL) are two effective modalities for the treatment of pigmentary disorders; however, the efficacy and safety levels of both treatments for AH have not yet been compared in a controlled study.
Aims
To evaluate and compare the efficacy and safety of the QS laser and IPL in the treatment of AH.
Methods
A randomized, split‐side study was conducted on 22 subjects; all subjects received a total of five split‐side treatments every 2 weeks. The efficacy was determined using the melanin index (MI), color chart level using the Pantone SkinTone™ Guide, improvement grading scale (IGS), and patient satisfaction scores at weeks 2, 4, 6, 8, and 10.
Results
The results showed that there was no significant difference in MI, color chart level, IGS, and patient satisfaction scores between the two treatments. Both treatments significantly improved AH after three sessions. However, the pain score was lower for IPL treatment. The adverse effects were transient and were found after IPL treatment in one participant (4.45%) who developed hyperpigmentation and another participant (4.45%) who developed erythema.
Conclusions
Intense pulsed light therapy is safe and effective for the treatment of AH, with no significant difference in the outcome compared with QS laser treatment.
•The Pulse-LD-intermittent-pumped acousto-optically Q-switched Tm:YAG laser is proposed.•The technology relies on precise time control among pulse laser diodes and Q-switch.•The technology relieves ...the thermal effect of Tm:YAG crystal.•Output pulse energy increases while ensuring the operation repetition of Tm:YAG laser.
An innovative pulse-diode-intermittent-pumped 2-µm acousto-optically Q-switched Tm:YAG laser is presented for the first time, which can improve the output energy, while ensuring the operation repetition of laser. Maximum output energy of 6.83 mJ and minimum pulse width of 367.7 ns at Q-switched repetition rate of 200 Hz is obtained at pump energy of 86.2 mJ. The output wavelength is 2014.9 nm. The beam quality factor Mx2 is 1.48 and My2 is 1.59. The stability is larger than 98%.
•Ultra-broad supercontinuum source using SM-2000 fiber as the non-linear medium is demonstrated experimentally for the first time.•High peak power Self-Q-switched emission from figure nine Ytterbium ...doped fiber laser.•Such spectrum has a flatness better than 5 dB in the 1256–2141 nm range and spans more than an octave ∼ 856–2141 nm at −20 dB level excluding the main peak.
Intracavity supercontinuum generation based on self-Q-switch assisted by stimulated Brillouin scattering is experimentally demonstrated from an all-fiber Ytterbium laser in the form of figure-9 configuration. At 3 W of pump power, a supercontinuum (SC) extending from visible red light to beyond two microns is obtained. Such spectrum has a flatness better than 5 dB in the 1256–2141 nm range and spans more than an octave ∼ 856–2141 nm at − 20 dB level excluding the main peak. The proposed SC laser source comes in a compact, simple, and low-cost design which could find application in areas such as spectroscopy, microscopy, and biomedical imaging.
The current need for coherent light sources for integrated (nano)photonics motivates the search for novel laser designs emitting at technologically relevant wavelengths with high‐frequency stability ...and low power consumption. Here, a new monolithic architecture that integrates monolayer MoS2 and chains of silver nanoparticles on a rare‐earth (Nd3+) doped LiNbO3 platform is developed to demonstrate Q‐switched lasing operation at the nanoscale. The localized surface plasmons provided by the nanoparticle chains spatially confine the gain generated by Nd3+ ions at subwavelength scales, and large‐area monolayer MoS2 acts as saturable absorber. As a result, an ultra‐compact coherent pulsed light source delivering stable train pulses with repetition rates of hundreds of kHz and pulse duration of 1 µs is demonstrated without the need of any voltage‐driven optical modulation. Moreover, the monolithic integration of the different elements is achieved without sophisticated processing, and it is compatible with LiNbO3‐based photonics. The results highlight the robustness of the approach, which can be extended to other 2D materials and solid‐state gain media. Potential applications in communications, quantum computing, or ultra‐sensitive sensing can benefit from the synergy of the materials involved in this approach, which provides a wealth of opportunities for light control at reduced scales.
Self‐Q switched nanolasing is demonstrated by developing a compact monolithic solid‐state laser platform. The device combines the optical gain delivered by Nd3+:LiNbO3 crystal, the extreme spatial confinement supplied by plasmonic Ag nanoparticle chains, and the temporal control provided by a single layer MoS2 acting as a saturable absorber. Stable and high‐quality short laser pulses are achieved at the nanoscale.
