Solid-state laser passively Q-switched in a new geometry

A new passive Q-switching geometry of a laser cavity has been proposed. In the proposed scheme, the volume of the passive Q-switch just partially overlaps the intracavity laser beam cross-section, leading, however, to the entire beam modulation. This technique was applied for passive Q-switching of a flash-lamp pumped multimode YAG:Nd³⁺ laser by LiF:F₂⁻ crystals. The giant pulse laser action threshold has been detected in the proposed geometry, and is lower than that in the scheme where the passive Q-switch operates in the traditional manner. Stable giant pulse oscillation of 1064 nm wavelength with a pulse duration of 24 ns, pulse energy of 450 mJ, and pulse repetition rates of up to 100 Hz, have been obtained.     

All-fiber passively Q-switched low-threshold erbium laser

A novel all-fiber passively Q-switched erbium laser with a Co(2+):ZnSe crystal as a saturable absorber is demonstrated experimentally. A pump power threshold of 20.5 mW, which the authors believe is the lowest to date, has been measured. Giant pulses with energy of 3.6 nJ and peak power of 0.7 mW have been obtained.     

Coupled-cavity passively Q-switched two-Stokes microchip laser

Experimental and theoretical studies of the coupled-cavity diode-pumped Nd:YAG/Cr:YAG microchip lasers with intracavity Raman conversion of laser pulses in a Ba(NO₃)₂ crystal into two Stokes pulses have been made. Two lasers with a different cavity length have been investigated. The minimal pulse durations at the 2nd Stokes wavelength were ??100 ps in the short-cavity laser at pulse energy of 5???J, and the pulse repetition rate reached 20?C24?kHz. The laser and Stokes pulse dynamics, as well as the spatial intensity distribution of the laser and the 1st Stokes beams at the output mirror have been recorded. A model describing such coupled-cavity microchip Raman lasers has been developed. The numerically simulated laser and Stokes pulse dynamics, and the calculated pulse energy, duration, and repetition rate are in good agreement with the experimental data.     

LD-pumped single-frequency passively Q-switched green laser

A LD-pumped single-frequency passively Q-switched Nd: YVO₄/KTP/Cr:YAG green laser is presented. Cr:YAG plays the double role of a passive Q-switch and a Brewster plate. With 900 mW incident pump laser, single-frequency passively Q-switched green laser with average power of 86 mW, pulse width of 14.7 ns, repetition rate of 140.8 kHz and peak power of 41.6 W is obtained. Measurement shows that the pulse amplitude and period between pulses are stable within ±1.5%.     

The pulse shape of a passively Q-switched microchip laser

The shape of the intensity pulse of a passively Q-switched microchip laser is investigated numerically and analytically. Our analysis is motivated by independent microchip laser experiments exhibiting nearly symmetric pulses in the case of a semiconductor saturable absorber and asymmetric pulses in the case of a solid state saturable absorber. Asymptotic methods are used to determine limiting behaviors of the pulse shape for both symmetric and asymmetric pulses. In the first case, we determine a sech² solution parametrized by one parameter which can be determined by solving two coupled nonlinear algebraic equations. In the second case, the pulse solution is decomposed into two distinct approximations exhibiting different amplitude and time scales properties. We review earlier approximations of the repetition rate and the pulse width. Received 2 August 1999     

Model of CW pumped passively Q-switched laser

An analytical model of a CW pumped passively Q-switched laser in plane wave approximation is presented. The model was based on possibility to express the analytical solution of simplified rate equations with the help of LambertW function. The LambertW function is now commonly available in most of mathematical software and became to be easy to use. The significant simplification of saturable absorber dynamics is made and its presence is described only by its initial and saturated transmission. Using this model it is possible to estimate giant pulse parameters, like pulse length and energy density, the pulse repetition rate, and the laser input-output power characteristic. The validity limits of this model were verified using numerical solution of more complicated rate equations model which included nonlinear response of the modulator. The model was compared with experimental results obtained for passively Q-switched diode pumped Nd:YAG/V:YAG microchip laser.     

56-ps passively Q-switched diode-pumped microchip laser

We passively Q switched a diode-pumped Nd:YVO4 microchip crystal with an antiresonant Fabry-Perot saturable absorber and achieved single-frequency pulses as short as 56 ps. We can vary the pulse width from 56 ps to 30 ns and the repetition rate from 27 kHz up to 7 MHz by changing the design parameters of the saturable absorber and the pump power.     

Radially polarized and passively Q-switched fiber laser

We report, for the first time to our knowledge, a radially polarized and passively Q-switched Yb-doped fiber laser. By using a Cr(4+):YAG crystal as a saturable absorber and a photonic crystal grating as a polarization mirror, a radially polarized pulse is produced, which has 202 W of peak power, 75 ns duration, and ~92% polarization purity at a 56.6 kHz repetition rate. The Q-switched pulse with radial polarization from the fiber laser would facilitate numerous applications.     

Graphene-based passively Q-switched dual-wavelength erbium-doped fiber laser

We demonstrate a compact Q-switched dual-wavelength erbium-doped fiber (EDF) laser based on graphene as a saturable absorber (SA). By optically driven deposition of graphene on a fiber core, the SA is constructed and inserted into a diode-pumped EDF laser cavity. Also benefiting from the strong third-order optical nonlinearity of graphene to suppress the mode competition of EDF, a stable dual-wavelength Q-switching operation has been achieved using a two-reflection peak fiber Bragg grating as the external cavity mirror. The Q-switched EDF laser has a low pump threshold of 6.5 mW at 974 nm and a wide range of pulse-repetition rate from 3.3 to 65.9 kHz. The pulse duration and the pulse energy have been characterized. This is, to the best of our knowledge, the first demonstration of a graphene-based Q-switched laser.     

On combined diode pumping of a passively Q-switched solid-state laser

Peculiarities of using combined diode pumping consisting of continuous wave (CW) and pulsed components in a diode-pumped solid-state (DPSS) laser with intracavity saturable absorber are studied. The requirements to pumping parameters for Q-switched operation are stated. The threshold optical pump energy and the diode-pumping time are investigated.     

被动调Q激光器优化的研究

被动调Q激光器以其结构简单、紧凑而获得了广泛的应用。为优化其性能参数,在总结近些年被动调Q基本理论基础上,对于具有能量上转换(Energy-transfer upconversion)的激光工作物质构成的被动调Q激光器,提出了可以将能量上转换引起的损耗归到线性损耗中进行优化设计的方法,并给出了输出镜的反射率和饱和吸收体的小信号透过率两者优化选择的直接关系图。根据被动调Q激光器的特有参数α,在总结提高调Q峰值功率的方法基础上,得出当α接近无穷大时,从被动调Q过渡到主动调Q,实现了被动调Q和主动调Q理论的统一。     

LD-pumped passively Q-switched red laser at 660 nm

A laser diode (LD) pumped Nd:YAG red pulse laser at 660 nm was presented by V:YAG passively Qswitching and LBO intracavity frequency doubling. With 1.6-W incident pump power, average output power of 46-mW, pulse duration (FWHM) of 23.3 ns, pulse repetition rate of 21.6 kHz, peak power of 91.4 W, and single pulse energy of 2.13μJ were obtained. The beam quality factor M2 was less than 1.2. The fluctuations of pulse energy and repetition rate were less than 3% in 4 hours. The pulsed laser at 660 nm is expected to be used as the pump source of Cr3+:doped crystal to obtain the gain-switched tunable laser.     

A passively Q-switched Yb:YAG microchip laser

We present a diode-pumped passively Q-switched Yb:YAG microchip laser, using a semiconductor saturable absorber mirror. We obtained pulses with 1.1-μJ energy, 530-ps duration, 1.9-kW peak power, and a repetition rate of 12 kHz. The laser is oscillating in a single longitudinal mode. Received: 23 October 2000 / Published online: 7 February 2001     

Efficient passively Q-switched Yb:LuAG microchip laser

An efficient passively Q-switched Yb:LuAG microchip laser with Cr4+:YAG as saturable absorber was demonstrated for the first time to our knowledge. Slope efficiencies of 40% and 28% were measured for the initial transmission of Cr4+:YAG, T(0)=95% and 90%, respectively. Laser pulses with a pulse energy of 19 microJ and a pulse width of 610 ps at the repetition rate of 12.8 kHz were achieved for T(0)=90%; the corresponding peak power of over 31 kW was obtained. The lasers oscillated at two or three longitudinal modes owing to the broad emission spectra of Yb:LuAG and mode selection by Cr4+:YAG thin plate acting as an intracavity etalon.     

Graphene passively Q-switched Ho:YAG ceramic laser

We report on the first graphene passively Q-switched Ho:YAG ceramic laser with central wavelength of 2,097 nm. Stable pulses of 28–64 kHz repetition rate and 2.6–9 μs pulse widths were generated under 1,907 nm thulium fiber laser pumping. Maximum average power of 264 mW with 9.3 μJ pulse energy was obtained under 3.27 W of pump power.     

Thermal mode-switching of a passively Q-switched microchip Nd:YAG laser

In the present article, the thermal distribution inside the gain medium of a passively Q-switched microchip laser is modeled and simulated for actual practical values associated with an available microchip laser constructed in our laboratory. The effects of the non-uniform heat distribution on the spectral properties of the output laser beam have been investigated and simulated with the variation of diode-pump power and pulse repetition rate. It is observed that the gain bandwidth as well as Optical Path Difference (OPD) values of the propagating pulses are significantly decreased, while the Nd:YAG chip is cooled down to a certain value. The validity of the utilized model is checked by setting and characterizing the spectral properties of a fabricated laboratory microchip laser under different heating conditions. It is verified that when the temperature of the gain material is changed by an electronically controlled Peltier device, the spectrum of the output laser beam can be switched between single- and dual-mode situations. This physical character has shown good agreement between the presented model and obtained experimental results.     

Watt-level continuous-wave and passively Q-switched red lasers pumped by a single blue laser diode

Praseodymium-ion-doped gain materials have the superiority of lasing at various visible wavelengths directly.Simple and compact visible lasers are booming with the development of blue laser diodes in recent years. In this Letter, we demonstrate the watt-level red laser with a single blue laser diode and Pr:YLiF_4 crystal. On this basis,the passively Q-switched pulse lasers are obtained with monolayer graphene and Co:ZnO thin film as the Q-switchers in the visible range.     

Compact diode-pumped passively Q-switched tunable Er-Yb double-clad fiber laser

Efficient repetitive passive Q switching of a cladding-pumped Er-Yb fiber laser has been demonstrated by use of an external-cavity configuration containing a Co(2+): ZnS crystal as a saturable absorber. Energies of as much as 60muJ in pulses of durations as short as 3.5 ns (FWHM), corresponding to a peak power of >10kW, have been generated, and the maximum slope efficiency with respect to the absorbed pump power was 13%. Using a bulk diffraction grating in the Littrow configuration to provide wavelength-selective feedback, we tuned the passively Q -switched fiber laser over 31 nm from 1532 to 1563 nm. The prospects for further improvement in performance are discussed.     

Graphene-based passively Q-switched diode-side-pumped Nd:YAG solid laser

In this paper, a desirably simple, convenient and inexpensive saturable absorber mirror has been fabricated based on graphene, which has no wavelength selectivity. Moreover, there are no changes in the structure and characteristics of graphene. By inserting the graphene-PMMA SA mirror to the Nd: YAG laser, the shortest pulse width of 260 ns can be obtained with the single-pulse energy of about 8.32 μJ. The experimental results prove that our graphene-PMMA SA mirror is feasible and suitable for Q-switched lasers.     

High-power MoTe_2-based passively Q-switched erbium-doped fiber laser

Materials in the transition metal dichalcogenide family, including WS_2, MoS_2, WSe_2, and MoSe_2, etc., have captured a substantial amount of attention due to their remarkable nonlinearities and optoelectronic properties.Compared with WS_2 and MoS_2, the monolayered MoTe_2 owns a smaller direct bandgap of 1.1 eV. It is beneficial for the applications in broadband absorption. In this letter, using the magnetron sputtering technique, MoTe_2 is deposited on the surface of the tapered fiber to be assembled into the saturable absorber. We first implement the MoTe_2-based Q-switched fiber laser operating at the wavelength of 1559 nm. The minimum pulse duration and signal-to-noise ratio are 677 ns and 63 dB, respectively. Moreover, the output power of 25 mW is impressive compared with previous work. We believe that MoTe_2 is a promising 2D material for ultrafast photonic devices in the high-power Q-switched fiber lasers.