Passive Q-switched Laser Research Articles

Q-switched Thulium-doped fibre laser using Bismuth (III) Telluride-based saturable absorber

We demonstrate a passive Q-switched thulium-doped fibre laser (TDFL) pulse generation using bismuth (III) telluride (Bi2Te3) thin film as saturable absorber. The Bi2Te3 was fabricated by a simple processing technique; simply by embedding the Bi2Te3 into the polyvinyl alcohol (PVA) film. By sandwiching 1 mm x 1 mm Bi2Te3 thin film between two fibre ferrules in a TDFL ring cavity, a stable Q-switching pulses train was generated. The repetition rate and pulse width were tuneable from 10.72 kHz to 39.9 kHz and 13.08 µs to 5.98 µs, respectively, as the pump power increased from 309 mW to 454 mW. The slope efficiency was 4.51%, while, the maximum pulse energy was calculated as 0.17 µJ.

Samarium (III) oxide thin film as a saturable absorber for the passively Q-switched Tm-doped fiber laser

We have demonstrated a passive Q-switched Thulium-doped fiber laser (TDFL using samarium oxide (Sm2O3) nanomaterial as saturable absorber (SA). The Sm2O3 based SA was fabricated by simply mixing the Sm2O3 powder solution with polyvinyl alcohol (PVA) solution. The homogeneously mixed solution was spread and dry to form a thin film. A piece of 1 mm x 1 mm of the SA thin film is sandwiched between two fiber ferrules and incorporated into a TDFL ring cavity for pulses generation. By controlling the loss and gain in the cavity, stable Q-switching operation was generated. The repetition rate was tunable from 17.62 kHz to 29.20 kHz by varying the pump power from 619 mW to 784 mW. The smallest pulse width of 3.54 µs and the highest pulse energy of 0.20 uJ were obtained at the highest pump power.

Active–passive Q-switched fiber laser based on graphene microfiber

We report an active–passive Q-switched laser based on graphene-covered microfiber modulator. The graphene-covered microfiber not only serves as a passive saturable absorber in a single laser cavity, but also can be used as an all-optical modulation device to synchronize two pulses generated from different wavelengths. The laser can not only actively change the output frequency of the Q-switched pulse to achieve the repetition frequency reduction, but also compress the pulse and increase the peak power of the output pulse. We successfully achieve the output of the active–passive Q-switched pulse using this fiber laser with a repetition rate from 41.1 kHz to 50.5 kHz. The fiber laser has potential applications in simultaneous output of multi-wavelength pulse.

Passively Q-switching fiber lasers using acetone solution as a saturable absorber

Organic materials are attracting attention for their potential applications due to their large third-order optical nonlinearities. A passive fiber Q-switching laser has been demonstrated based on an erbium/ytterbium codoped amplifier and an acetone solution saturable absorber (SA). When pump power was increased from 120 to 155 mW, the repetition rate increased from 5.68 to 16.67 kHz, while the pulse width decreased from 24.1 to 15 μs. These results indicate that acetone solution can be used as an effective SA for pulsed lasers.

A compact and portable laser radioactive decontamination system using passive Q-switched fiber laser and polygon scanner

We designed a compact and portable laser radioactive decontamination system using a passive Q-switched fiber laser and a polygon scanner. The passive Q-switched fiber laser produced average power of 15 W at a repetition rate of 60 kHz. The scanner system contained a 12-sided spinning polygon mirror driven by a DC motor. By varying the spinning speed of the polygon mirror, we achieved a processing speed of up to 88,500 mm/s. This system was demonstrated to be very efficient for radioactive decontamination on surfaces of various metals: stainless steel, brass, iron, and aluminum.

Influence of Absorption cross section of saturable absorber on Passive Q-switching laser pulse characteristics

Influence of Absorption cross section of saturable absorber on Passive Q-switching laser pulse characteristics

Bifurcation and nonlinear dynamics in passive Q-switched optical vortex lasers

In a laser resonator with an intra-cavity spiral phase plate, a passive Q-switched pulsed vortex laser carrying a positive unit topological charge is formed by the coherent superposition of the supported off-axis multiple-pass transverse (MPT) resonant modes. Under different pumping conditions, the modal interaction induces spatiotemporal instability and results in periodic and aperiodic oscillations in the vortex laser pulses while the vortex structure remains stable. The constituting off-axis MPT modes that form the vortex strongly overlap in the time domain and can be simulated by a modified Tang–Statz–DeMars model including coherent modal interactions. Expected potential applications using this vortex laser include the manipulation of laser chaos and stochastic events.

Passively Q-switched laser action of Yb:LaCa4O(BO3)3 crystal

We report on the passive Q-switching laser performance of Yb:LaCa4O(BO3)3 crystal with Cr4+:YAG or two-dimensional (2D) MoS2 acting as a saturable absorber. With Cr4+:YAG, a pulsed output power of 3.8 W was produced at 71 kHz with a slope efficiency of 49%, whereas at a lower repetition rate, the average pulse energy achieved could reach 250 µJ; the shortest duration and peak power were respectively 17 ns and 14.7 kW. For passive Q-switching with 2D MoS2, 1.61 W of pulsed output power was achieved at 395 kHz; the resulting pulse energy, duration, and peak power were 4.1 µJ, 220 ns, and 18.6 W, respectively.

Study the effect of output coupler mirror reflectivity on Stokes Raman laser pulse characteristics

The effect of output coupler mirrors reflectivity on characteristics of Stokes Raman pulse, which is generated from passive Q-switching intracavity Raman media laser system has been studied. A software computer program based on this study to solve the rate equations of instantaneous performance of the mentioned system (Nd:YVO4, Cr+4:YAG and BaWO4 ) numerically by Runge- kutta-Fehalberg method. The study shows that the energy, duration, and the power of the pulse increasing when the output coupler mirrors reflectivity increasing.

Tin diselenide-based saturable absorbers for eye-safe pulse lasers

Eye-safe pulse lasers have attracted increasing attention due to their potential wide application in many fields. However, optical modulators with excellent nonlinear optical absorption properties in the range of 1.4–2.1 μm are still very scarce. In this study, tin diselenide (SnSe2), a newly-developed 2D layered semiconductor material with facile processability and low cost, was investigated. The nonlinear optical response of SnSe2 was investigated using the open aperture Z-scan method at 1500 and 1800 nm. Using SnSe2 as the saturable absorber, a passive Q-switched solid-state laser was realized at 1.3 and 1.9 μm for the first time. This study proved SnSe2 to be an effective optical modulating material for the eye-safe waveband.

Few-layer MXene Ti3C2Tx (T = F, O, or OH) saturable absorber for visible bulk laser

The novel two-dimensional MXenes have been investigated in the photonics field in areas such as broadband nonlinearity, pulse laser generation and passive photonic diode, and so on. In this contribution, the nonlinear optical response at the visible band and the demand pulse laser generation based on MXenes was initially realized. The few-layer MXene Ti3C2Tx was fabricated and utilized as a saturable absorber (SA) to realize passive Q-switched visible bulk laser covering the spectral range of orange (607 nm), red (639 nm), and deep red (721 nm). At the three wavelength, the maximum average output powers and the shortest pulse widths were (111 mW, 426 ns) for 607 nm, (150 mW, 264 ns) for 639 nm, (115 mW, 328 ns) for 721 nm, respectively. Our experimental results indicate the MXene Ti3C2Tx SA could be an efficient and promising optical modulator in the visible domain.

Development of a subsurface LIBS sensor for in situ groundwater quality monitoring with applications in CO2 leak sensing in carbon sequestration

Sub-surface activity such as geologic carbon sequestration (GCS) has the potential to contaminate groundwater sources with dissolved metals originating from sub-surface brines or leaching of formation rock. Therefore, a Laser Induced Breakdown Spectroscopy (LIBS) based sensor is developed for sub-surface water quality monitoring. The sensor head is built using a low cost passively Q-switched (PQSW) laser and is fiber coupled to a pump laser and a gated spectrometer. The prototype sensor head was constructed using off the shelf components and a custom monolithic, PQSW laser and testing has verified that the fiber coupled design performs as desired. The system shows good calibration linearity for tested elements (Ca, Sr, and K), quick data collection times, and Limits of Detection (LODs) that are comparable to or better than those of table top, actively Q-switched systems. The fiber coupled design gives the ability to separate the PQSW LIBS excitation laser from the pump source and spectrometer, allowing these expensive and fragile components to remain at the surface while only the low-cost, all optical sensor head needs to be exposed to the hostile downhole environment.

Growth, spectroscopic properties and laser performances of Yb:La0.11Y0.89VO4 and Yb:La0.15Y0.85VO4 crystals

0.45 at. % Yb doped La0.11Y0.89VO4 and La0.15Y0.85VO4 mixed crystals were grown by the Czochralski method, the structures and polarized spectroscopic properties were systematically studied. The fluorescence lifetimes of these two crystals were 355 and 374 μs, respectively. Continuous wave laser performances of the a-cut mixed crystals were demonstrated, with Yb:La0.11Y0.89VO4, a maximum output power of 1.97 W was achieved at the absorbed pump power of 7.58 W. Passive Q-switched laser with MoS2 as saturable absorber was also achieved, and the maximum average output power was 82 mW at a repetition rate of 200 kHz with a slope efficiency of 20%.

Pulse delay-controlled passive Q-switched laser with tunable pulse width

We present a method for obtaining a passive Q-switched Nd : YAG / Cr4 + : YAG laser with tunable pulse width. The output pulse width is tuned based on the delay time between the pumping pulse and trigger pulse. An auxiliary laser with a narrow pulse is used to trigger the laser pulse generation at different delay times during the pumping pulse duration. It is found that the output pulse width can be continuously adjusted from 1415 to 562 ps with an output peak power ranging from 44 to 240 kW at a fixed pumping power. The beam quality factor M2 is kept <1.5 with changing of the pulse width.

Laser-Diode Pumped Passive Q-Switched Laser with Quick Tunable Pulse-Width Capability

A laser-diode pumped passive Q-switched Nd:YAG/Cr4+:YAG laser with quick tunable pulse-width capability is studied and experimentally demonstrated. By focusing the auxiliary controlling laser beam onto a Cr4+:YAG crystal and thereby changing the initial transmission of the Cr4+:YAG crystal, laser pulses with different pulse widths can be achieved. The obtained laser pulse width is tunable in the range of 550–1492 ps with a fixed cavity length of 7 mm. The laser can be used to achieve different pulse widths between two pulses in the range of sub-nanosecond to a few tens of nanoseconds.

Magnetron sputtered Al-doped ZnO thin film as saturable absorber for passively Q-switched Er/Yb double clad fiber laser

The passive Q-switched operation of a ring cavity Er/Yb-doped double clad fiber laser by using an Al-doped ZnO (AZO) thin film as saturable absorber is experimentally demonstrated. In order to improve the absorbance in the C-band wavelength region, a thin film of AZO containing Zn and Al metal precursors in a proportion of 98:2 wt% was developed by an radio-frequency (RF) magnetron sputtering process. Then the AZO film was used as a saturable absorber (SA) in a ring cavity Er/Yb double clad fiber laser. The AZO-SA exhibits a modulation depth of 11.3% and a saturation intensity of 0.057 MW cm−2 in the 1.55 µm waveband. In a pump power range from 0.475 to 1.356 W, stable Q-switched pulse trains with repetition rates of 70.1–161.3 kHz were observed. With a maximum pump power of 1.356 W, a minimum pulse width of 1.12 µs and a maximum pulse energy of 1.32 µJ are obtained. To the best of our knowledge, we present the first demonstration of a passive Q-switching laser operation using an RF sputtered AZO thin film as a saturable absorber. The reliability of the RF magnetron sputtered AZO thin films used as an SA for 1.55 µm Q-switched laser applications is experimentally demonstrated.

MoSSe Saturable Absorber-Based High-Power Passively Q-Switched &lt;inline-formula&gt; &lt;tex-math notation="LaTeX"&gt;$2.0~\mu$ &lt;/tex-math&gt; &lt;/inline-formula&gt;m Bulk Laser

A ternary transitional metal dichalcogenides alloy material, molybdenum sulphoselenide (MoSSe), has been successfully fabricated and used as a saturable absorber (SA) for a passively Q-switched (PQS) Tm:YAP bulk laser operating at $2.0~\mu \text{m}$ for the first time, to best of our knowledge. The open aperture Z-scan method was used to characterize the saturable absorption properties of the prepared MoSSe SA. The maximum average output power and pulse repetition rate, shortest pulse width, highest single pulse energy, and highest pulse peak power of this laser were 2.26 W, 95 kHz, 303 ns, $24.2~\mu \text{J}$ , and 80 W, respectively. The results are distinguished from other two-dimensional materials-based $2.0~\mu \text{m}$ PQS lasers, indicating that MoSSe could be a promising material for generating high power and short pulse width lasers in the $2.0~\mu \text{m}$ spectral range.

Dynamic cavity effects in topological insulator Bi2Te3 based passive Q-switched solid state laser

In this work, a comprehensive investigation of dynamic evolution for pulsed solid state laser using topological insulator as saturable absorber (SA) is reported. Without material damage, dynamic transition from Q-switched (QS) state to continuous wave (CW) state in the laser cavity is observed when the pumping rate to the Nd3+:YAG laser crystal increases. With a sufficiently large pumping rate, the initiated laser spiking damps and relaxes to CW state similar to a laser system without intra-cavity SA. Formulated by well-known laser rate equations, analysis of the perturbations around fixed points reveals the instability spectrum that is able to explain the observed transition in experiments. Theoretically, the parameters space to support QS operation are given in terms of the ratio of saturation intensity of laser gain media over the saturation intensity of SA, pumping speed, the ratio of relaxation time of laser gain media over cavity lifetime and the modulation depth of the SA. The result of this work suggests a simple approach to understand passive Q-switched (PQS) laser with SAs of low saturation intensity and guidelines to the design of laser system employing low-saturation materials as SA, such as two-dimensional TI material.

All-fiber passively Q-switched erbium fiber laser implementing erbium-ytterbium-thulium co-doped saturable absorber fiber

We demonstrate a passive Q-switched fiber laser using an erbium-ytterbium-thulium (Er-Yb-Tm) doped fiber. The length of the Er-Yb-Tm co-doped fiber is varied from 0.4 m to 1.4 m to study the effect of this passive gain medium for pulse laser performance. The proposed laser operates in the pulse operation regime within a certain range of pump powers, which is dependent on the length of the Er-Yb-Tm co-doped fiber. A longer fiber employed in the laser cavity results in a higher laser pump power threshold, but a wider pump power range of pulse laser operation. The experimental outcome shows that a 1.0 m Er-Yb-Tm co-doped fiber offers the best performance in this work with a Q-switched pump power threshold of 45.1 mW, the widest pulse energy output range of 0.0439 μJ from 0.0167 μJ to 0.0606 μJ, with the supplementary advantage of 120.7 mW Q-switched laser operating range. This fiber gain medium analysis contributes to the generation of short pulse laser source without employing any chemical materials and complex laser setup.

Passively Q-Switched Thulium-Doped Fiber Laser Using Alcohol

A passively Q-switched thulium-doped fiber laser using isopropyl alcohol as a saturable absorber is experimentally demonstrated. The absorber was made of two FC/PC connectors matched into a cannula with the gap between them filled by isopropyl alcohol. The alcohol-based saturable absorber incorporated into a ring cavity thulium-doped fiber laser leads to passive Q-switching laser operation at the wavelength of 1.88 μm. With the maximum pump power of 1.42 W, passive Q-switched pulses with a minimum duration of 1.46 μs, maximum repetition rate of 66.7 kHz and pulse energy of 0.93 μJ were obtained.