Q-switched Solid-state Laser Research Articles

Influence of Opening Time Interval of Gate Signals on Suppression of Horizontally Polarized Signal of Infrared Pulsed Laser.

Since the beginning of the 21st century, infrared Nd:YVO4 pulsed lasers have been widely applied, especially in some actual industrial processes. In the working process of a laser-aided etching device, the "match-head" effect must be effectively controlled by suppressing the first giant pulse for a solid-state Q-switched laser. In the process of optimizing the infrared Nd:YVO4 pulsed laser by adjusting the slope parameters of the radio frequency (RF) modulation to suppress the first giant pulse, it has been found that an abnormal horizontally polarized emission with a very short time appears before the formal vertically polarized emission when the gate signal is artificially started. Actually, abnormal horizontally polarized emissions will bring some unexpected machining traces during the production process and even greater dangers. The experimental results show that with the increase in the slope duration of an RF signal, the existence time of abnormal output horizontally polarized light will be shortened, and the horizontal giant pulse and vertical giant pulse are well suppressed. When the slope duration is greater than 0.18 ms, both horizontal and vertical giant pulses will disappear. The horizontally polarized light can be thoroughly suppressed when the slope duration is greater than 13.7 ms. Compared with the method of adding a polarizer to eliminate abnormal output horizontally polarized light, this method does not add elements in the laser, ensuring that the laser volume is relatively small, and does not affect the quality of the normal output laser. The research conclusion is thought to be of great practical significance, especially for processing transparent materials.

1.4 W Passively Q-Switched Mode-Locked Tm:CALGO Laser with a MoS2 Saturable Absorber

The passively Q-switched mode-locked (QML) operation of a Tm:CaGdAlO4 (Tm:CALGO) bulk laser pumped by a wavelength-tunable Ti:sapphire oscillator using molybdenum disulfide (MoS2) as a saturable absorber was demonstrated. By using an output coupler with 3% transmittance, Q-switched mode-locked operation can be achieved with 3.56 W absorbed pump power. At a pump power of 6.77 W, laser pulses with the maximum average power of 1.44 W were obtained, corresponding to a slope efficiency of 21.3%. The laser delivered pulses centered at 1927 nm with a repetition frequency of 131.6 MHz. The experimental results confirm the promising application of the MoS2 in high-power Q-switched mode-locked solid-state lasers at 2 µm.

CH3NH3PbBr3 as a saturable absorber for infrared passively Q-switched solid-state laser

Perovskite materials are used in the field of lasers and can achieved good results. In this paper, we prepared an organic–inorganic hybridized CH3NH3PbBr3 saturable absorber (SA). Continuous wave (CW) Tm:YAP solid-state lasers with CH3NH3PbBr3-SA successfully obtained pulsed lasing at 1987.5 nm after continuous tuning. In CW mode, the maximum absorbed pump power by the laser was 19.42 W, which corresponds to 0.68 W output power. The central output wavelength of the continuous wave laser was 1989.9 nm. In PQS mode, the output power of laser was 203 mW. Under the condition of maximum repetition frequency of 45 kHz, the narrowest pulse width of the PQS laser were 1.16 μs. Meanwhile, the laser produced a maximum single-pulse energy (4.5 μJ) and a maximum peak power (3.9 W). The beam quality factors (the horizontal/vertical directions) were M2 x = 1.1 and M2 y = 1.39. The CH3NH3PbBr3 was an excellent SA for infrared PQS solid-state lasers, which had a large potential for development applications in the field of lasers.

Seedless synthesis of Au nanoplates with tunable plasmonic peaks

Au nanoplates with tunable in-plane dipolar localized surface plasmon resonance peaks in a broad range from the visible to near-infrared region were obtained in high yield using a seedless wet chemical growth method after purification. Cetyltrimethylammonium chloride was used as a surfactant, while hydrogen peroxide and sodium borohydride were used as the weak and strong reducing agents, respectively. The edge length and in-plane dipolar localized surface plasmon resonance peak of the Au nanoplates could be adjusted by varying the amounts of hydrogen peroxide and sodium borohydride. The Au nanoplates were further used as the saturable absorber to generate pulsed laser output in a passively Q-switched solid-state laser at approximately 2 µm. Our study offers a new method for obtaining Au nanoplates with tunable plasmonic peaks over a broad range.

30-100 kHz, 2 ns passively Q-switched laser for fast and efficient photoacoustic microscopy.

Actively Q-switched (AQS) fiber laser and solid-state laser (SSL) are widely used for photoacoustic microscopy (PAM). In contrast, passively Q-switched (PQS) SSL not only maintains most of the merits of AQS lasers, but also exhibits unique advantages, including the pulse width (PW), pulse repetition rate (PRR) tunability, wavelength, compactness, and cost. These advantages all benefit the PAM. However, there are few reports demonstrating the performance of PQS-SSL on PA imaging. Here, we demonstrate a compact PQS-SSL for fast and efficient PA imaging. The laser uniquely maintains a constant PW (~2 ns) and pulse energy (~3 μJ) during the PRR variation (30-100 kHz), which is valuable for preserving a stabilized imaging performance at different scanning rates. The PA imaging performance is compared by a resolution target and showcased by whole-body scanning of an embryonic zebrafish in vivo. The performance indicates that PQS-SSL is a promising candidate for PAM.

Simulation of spatial rogue waves in actively Q-switched solid-state laser with transverse mode locking

We report the generation of spatial rogue waves in the actively Q-switched Nd:YAG laser with several transverse modes and negligible nonlinear effects in the cavity. We discuss a basic theoretical model that is able to reproduce the experimental observations of spatial rogue waves in the output Q-switched pulses as a result of the coherent superposition of transverse modes. The simulated rogue wave statistics depends on the configuration of the lasing modes and take a more pronounced L-shaped form in the case of highly anisotropic mode distribution and reduced frequency spacing between the modes. For larger frequency spacing between the modes, the mode-locking effects result in the periodic dynamics of the transverse beam profile and formation of spatio-temporal rogue waves. These results indicate that transverse mode-locking and spatial symmetry breaking through anisotropy in the mode configuration represent factors responsible for spatial rogue wave emergence in multimode lasers with low nonlinearity.

An infrared passively Q-switched laser based on graphene/BN heterojunction

Passively Q-switched solid-state lasers (PQSL) can obtain output lasers with narrow pulse widths and high peak powers, where play a vital role in the information society. Saturable absorbers (SA) are an essential part of passively Q-switched solid-state lasers. In this paper, we demonstrated 2 μm passively Q-switched (PQS) solid-state laser based on a graphene/BN heterojunction saturable absorber. In the experiments, we used two output mirrors with transmittance of 1.5 %/2.5 % for comparative study. We also used monolayer graphene as saturable absorber for experiment to compared with graphene/BN saturable absorber. The experimental results showed that the best passively Q-switched operation was achieved with the graphene/BN heterojunction saturable absorber at output mirror transmittance of 1.5 %. When the maximum absorption pump power was 1.49 W, the maximum average output power was 38 mW, corresponding with a slope efficiency of 5.4 %. At this point, the minimum pulse width was 1.56 μs, corresponding with a repetition frequency of 52 kHz. The single pulse energy and the peak power were calculated to be 730.36 nJ and 466.96 mW, respectively. The center wavelength of the PQS laser was 2066.8 nm. The experimental results showed that graphene/BN heterojunction was a promise saturable absorber in the field of 2 μm passively Q-switched solid-state lasers.

Generation of mode-switchable nanosecond pulsed cylindrical vector beams and vortex beams from a Q-switched solid-state laser

We reported and demonstrated a Q-switched solid-state laser for the generation of mode-switchable nanosecond pulsed cylindrical vector beams and vortex beams between different orders. In the cavity, an order-switchable Q-plate, consisted of two Q-plates and two quarter wave plates, was applied to achieve the mode-switch between two different orders by adjusting the angles of quarter wave plates. Besides, two extra quarter wave plates and a Faraday rotator were utilized to realize the intracavitary self-reproducibility of cylindrical vector beams and vortex beams, respectively. The experimental results show that by using two Q-plates of 1st and 3rd orders, the cylindrical vector beams and vortex beams of 2nd and 4th orders can be directly generated from the solid-state laser. For the 2nd order cylindrical vector beam and vortex beam, the slope efficiency, pulse width, and repetition rate are 7.2%, 415 ns, and 227 kHz, respectively. To the best of our knowledge, it is the first time to realize the controlled generation of mode-switchable cylindrical vector beams and vortex beams between two different orders from a solid-state laser.

Introducing a 2V-resonator for the improvement of pulse stability in a high-gain Q-switched Yb:YAG thin-disk laser.

Pulse instability in Q-switched solid-state lasers at enough high repetition rates is a significant problem for getting high powers. This issue is more critical for Thin-Disk-Lasers (TDLs) due to the smallness of round-trip gain in the thin active media. The main idea of this work is that increasing the round-trip gain of a TDL makes it possible to diminish its pulse instability at high repetition rates. Accordingly, a novel 2V-resonator is introduced to overcome the low gain of TDLs, in which the passage of the laser beam from the active media is twice that of the standard V-resonator. The experiment and simulation results indicate that the threshold of laser instability considerably improves for the 2V-resonator relative to the traditional V-resonator. This improvement is well seen for various time windows of the Q-switching gate and different pump powers. By choosing appropriate Q-switching time and pump power, the laser was stably run at 18 kHz, a recorded repetition rate for Q-switched TDLs.

Evolution of optical nonlinearity within a graphene/Bi2Te3 heterostructure

Effect of passive Q-switched solid-state laser for different absorption behaviours of absorbers.

High-Peak-Power Acoustic-Optic Q-Switched Solid-State Laser with Hermite-Gaussian Modes

High-Peak-Power Acoustic-Optic Q-Switched Solid-State Laser with Hermite-Gaussian Modes

Method and portable bench for tests of the laser optical calibration system components for the Baikal-GVD underwater neutrino Cherenkov telescope

The Large-scale deep underwater Cherenkov neutrino telescopes like Baikal-GVD, ANTARES or KM3NeT, require calibration and testing methods of their optical modules. These methods usually include laser-based systems which allow us to check the telescope responses to the light and for real-time monitoring of the optical parameters of water such as absorption and scattering lengths, which show seasonal changes in natural reservoirs of water. We will present a testing method of a laser calibration system and a set of dedicated tools developed for Baikal-GVD, which includes a specially designed and built, compact, portable, and reconfigurable scanning station. This station is adapted to perform fast quality tests of the underwater laser sets just before their deployment in the telescope structure, even on ice, without a darkroom. The testing procedure includes the energy stability test of the laser device, 3D scan of the light emission from the diffuser and attenuation test of the optical elements of the laser calibration system. The test bench consists primarily of an automatic mechanical scanner with a movable Si detector, beam splitter with a reference Si detector and, optionally, Q-switched diode-pumped solid-state laser used for laboratory scans of the diffusers. The presented test bench enables a 3D scan of the light emission from diffusers, which are designed to obtain the isotropic distribution of photons around the point of emission. The results of the measurement can be easily shown on a 3D plot immediately after the test and may be also implemented to a dedicated program simulating photons propagation in water, which allows us to check the quality of the diffuser in the scale of the Baikal-GVD telescope geometry.

Dual-wavelength controllable Q-switched Nd:GSAG laser with molybdenum disulfide saturable absorber

The present work successfully demonstrated a passively Q-switched solid-state 1 µm Nd:GSAG laser using a few layer molybdenum disulfide (MoS2) saturable absorber. Controllable dual wavelengths of 1059.94 nm and 1062.3 nm were achieved in the experiment. We obtained the shortest pulse width of 217 ns and the highest pulse repetition frequency of 51.2 kHz. The pulse energy and peak power are 9.5 μJ and 43.7 W, respectively. To our knowledge, this is the first time that dual wavelengths with a controllable intensity ratio have been obtained in a Q-switched solid-state laser based on a MoS2 saturable absorber at 1 μm. The results demonstrate that MoS2 is a highly reliable optical modulator for dual wavelength laser applications.

Electro-optic Q-switched Cr:LiSAF laser

We demonstrate electro-optic Q-switched solid state laser with Cr:LiSAF active medium. A single 50 ns pulse with 14 mJ of output energy is demonstrated. Simultaneous generation of several peaks with a step of 1.4 nm within the spectrum envelope with a full width at half maximum of 10.3 nm is demonstrated. For an electro-optic Q-switched mode a Pockels cell is used. Demonstrated laser can be used in differential absorption lidar systems.

Mxene Ti3C2Tx Langmuir–Blodgett films as saturable absorber for near-infrared Q-switched laser

MXene is a fast-growing family of 2D materials with unique light–matter interactions. Ti3C2Tx belongs to the family of MXene that show nonlinear saturable absorption characteristics and has been studied widely. However, translating the excellent performance of MXene flakes into stable thin film saturable absorbers (SA) devices has been a challenging task. Herein, we report the fabrication of a long term stable MXene Ti3C2Tx film SA deposited on a quartz plate by the Langmuir–Blodgett (LB) method for the first time, and it was used in passive Q-switched solid-state pulsed laser generation at the central wavelengths of 1.06 and 1.34 μm, respectively. LB Ti3C2Tx SAs exhibits excellent optical properties such as high modulation depth, low loss, and high linear transmittance at mid-infrared wavelengths. By inserting the LB Ti3C2Tx SAs into two Nd-doped solid-state lasers, short pulses were generated with the pulse duration of 244 ns and 311 ns in the 1.06 and 1.34 μm regimes, respectively. In addition, long-term stability was maintained in constant temperature drying. The results illustrate the potential of the MXene LB Ti3C2Tx SA films for laser applications, paving new ways for producing large-area, ultra-uniform, low-loss and stable MXene SA by the LB method.

Broadband few-layer niobium carbide MXene as saturable absorber for solid-state lasers

Recently, niobium-carbide (Nb2C) nanosheets, a member of MXene family, have gained significant attention because of their unique physical and chemical properties. Here, the few-layer Nb2C nanosheets were synthesized by a combination of selective etching and liquid cascade centrifugation. The broadband absorption properties of the few-layer Nb2C nanosheets were systematically investigated by the open-aperture Z-scan technique. The results indicate the excellent saturable absorption responses of Nb2C nanosheets, revealing the promising optical modulate application of Nb2C in solid-state lasers. Using the Nb2C saturable absorber (SA), passively Q-switched solid-state lasers from visible to near-infrared range were realized, which presented a promising alternative for a broadband optical modulator. Furthermore, a passively mode-locked laser at 1.06 μm was successfully achieved based on the Nb2C SA. A pulse duration of 13.5 ps was produced with the maximum average output power of 426 mW and a repetition rate of 99.1 MHz. To the best of our knowledge, this is the first time to use Nb2C nanosheets as a broadband SA for the solid-state lasers. The results may promote further applications of 2D optoelectronic materials from visible to near-infrared range.

Three-step seedless synthesis of ultralong gold nanorods

Ultralong gold nanorods with an average aspect ratio up to 77 and average length up to 1.6 μm were obtained by using the three-step seedless wet chemistry growth method. The prepared ultralong gold nanorods were pentatwinned. The effects of the amount transferred from flask B to C, and the pH value in the growth solution C on the synthesized ultralong gold nanorods were investigated by using the scanning electron microscopy images. Results showed that ultralong gold nanorods with tunable average aspect ratio from 24 to 77 were obtained by changing the amount transferred from flask B to C and the pH value in the growth solution C. Due to the large aspect ratio of the prepared gold nanorods, the longitudinal surface plasmon resonance wavelength of the ultralong gold nanorods was expected in the infrared wavelength region. Moreover, 2 μm mid-infrared pulsed laser output was achieved in a passively Q-switched solid-state laser by using the prepared ultralong gold nanorods as the saturable absorber. Our method offers a new facile strategy to obtain ultralong gold nanorods with tunable aspect ratios, which have wide applications in areas such as photonics and optoelectronics.

Pedagogically fast model to evaluate and optimize passively Q-switched Nd-doped solid-state lasers.

The coupled rate equations with the spatial overlap effect for four-level passively Q-switched lasers are fully considered. A transcendental equation is derived for the residual fraction of the inversion density after the finish of the Q-switched pulse. Comprehensive calculations for the transcendental equation were executed to attain an analytical function for precisely fitting the residual fraction of the inversion density. With the fitting function, a pedagogical model with the correction for high output coupling is developed to straightforwardly analyze the output pulse energy and peak power. Detailed experiments are carried out to validate the model.

MXene/Graphene Oxide Heterojunction as a Saturable Absorber for Passively Q-Switched Solid-State Pulse Lasers.

Owing to their unique characteristics, two-dimensional (2-D) materials and their complexes have become very attractive in photoelectric applications. Two-dimensional heterojunctions, as novel 2-D complex materials, have drawn much attention in recent years. Herein, we propose a 2-D heterojunction composed of MXene (Ti2CTx) materials and graphene oxide (GO), and apply it to an Nd:YAG solid-state laser as a saturable absorber (SA) for passive Q-switching. Our results suggest that a nano-heterojunction between MXene and GO was achieved based on morphological characterization, and the advantages of a broadband response, higher stability in GO, and strong interaction with light waves in MXene could be combined. In the passively Q-switched laser study, the single-pulse energy was measured to be approximately 0.79 µJ when the pump power was 3.72 W, and the corresponding peak power was approximately 7.25 W. In addition, the generation of a stable ultrashort pulse down to 109 ns was demonstrated, which is the narrowest pulse among Q-switched solid-state lasers using a 2-D heterojunction SA. Our work indicates that the MXene–GO nano-heterojunction could operate as a promising SA for ultrafast systems with ultrahigh pulse energy and ultranarrow pulse duration. We believe that this work opens up a new approach to designing 2-D heterojunctions and provides insight into the formation of new 2-D materials with desirable photonic properties.

Ti2CTx MXene as a Saturable Absorber for Passively Q-Switched Solid-State Lasers.

In this work, we successfully fabricated a transmissive saturable absorber (SA) with Ti2CTx MXene using the spin-coating method. By inserting the Ti2CTx saturable absorber into the diode-pumped solid-state (DPSS) Nd:YAG laser, a stable passively Q-switched operation was obtained near 1.06 μm. At a pump power of 4.5 W, we obtained the shortest pulse duration of 163 ns with a repetition rate of 260 kHz. The corresponding single pulse energy and peak pulse power were 3.638 μJ and 22.3 W, respectively. The slope efficiency and the optical conversion efficiency of the laser were 21% and 25.5%, respectively. To the best of our knowledge, this is the first time that Ti2CTx was used in the passively Q-switched solid-state lasers. This work demonstrates that Ti2CTx can be a promising saturable absorber for solid-state laser pulse generation.