Q-switched Mode-locked Pulses Research Articles

Multilayer graphene for Q-switched mode-locking operation in an erbium-doped fiber laser

We report the laser operation of Q-switched mode-locking (QML) in an erbium-doped fiber laser by using a multilayer graphene saturable absorber (SA), which consists of 22-layer of graphene fabricated by the chemical vapor deposition method. Based on our balanced twin detector measurement, the graphene sample is confirmed to show a saturable intensity of 3.375MW/cm2 and an absolute modulation depth of 40.27%. It is demonstrated that this graphene SA can readily produce high quality QML pulses. At the pump power of 391.9mW, the stable mode-locked pulse train with the Q-switched envelope repetition rate of 16.98kHz and the envelope width of 13.84μs are achieved. The maximal main pulse peak power can reach up to 35.89W. This verifies that the multilayer graphene can be still applied as an effective saturable absorber for passively Q-switched mode-locked operation.

A high-quality, monolayer graphene absorber for a 1.06 μm Q-switched mode-locking Nd:YVO4 laser

High-quality, monolayer graphene was grown by the chemical vapor deposition method. The monolayer graphene was used as a saturable absorber in a Nd:YVO4 laser. Stable Q-switched mode-locking laser pulses at a central wavelength of 1.06 μm were obtained. The maximum average output power and pulse repetition rate were 1570 mW and 142.8 MHz, respectively. Our results illustrate that graphene is a promising saturable absorber for solid-state lasers.

A Q-switched, mode-locked fiber laser using a graphene oxide-based polarization sensitive saturable absorber

We demonstrate the use of a graphene oxide (GO)-deposited D-shaped fiber as a polarization sensitive saturable absorber for the implementation of a stable Q-switched, mode-locked fiber laser. Using both features of nonlinear saturable absorption and large polarization dependence loss of GO-deposited D-shaped fiber, stable Q-switched mode-locked pulses are readily obtained from an erbium-doped fiber ring laser through simple intra-cavity polarization control under a fixed pump power. It is shown that bursts of sub-picosecond, mode-locked pulses with a Q-switching envelope of a ∼2.63 μs temporal width and a ∼71.3 kHz repetition rate can readily be generated from the laser. It is also demonstrated that the operating regime of the pulsed laser can be readily changed between mode-locking, Q-switched mode-locking, and Q-switching simply by changing the polarization state of the oscillated beam within the cavity.

Passively continuous-wave mode-locked Er^3+-doped ZBLAN fiber laser at 28 μm

An Er(3+)-doped ZrF(4)-BaF(2)-LaF(3)-AlF(3)-NaF (ZBLAN) fiber laser was passively mode-locked by inserting a Fe(2+):ZnSe crystal into the free space part of the cavity. Continuous-wave mode-locked pulses at 2.8 μm with a pulse duration of 19 ps estimated from the spectral bandwidth and an average power of 51 mW were generated when a collimated beam traversed the Fe(2+):ZnSe crystal, while Q-switched mode-locked pulses were obtained when the Fe(2+):ZnSe crystal was illuminated by the focused beam.

Q-switched mode-locking of an erbium-doped fiber laser using cavity modulation frequency detuning

We present the results of an investigation regarding a Q-switched mode-locked fiber laser scheme based on a cavity modulation frequency detuning technique. The approach is based on undamped laser relaxation oscillations occurring due to frequency detuning in the fundamental cavity resonance frequency. Through a range of experiments with an erbium-doped, fiber-based, ring-cavity laser, this approach has been shown to be capable of generating high-quality Q-switched mode-locked pulses from an optical fiber-based laser. The maximum frequency detuning range for a stable Q-switched mode-locking operation has been observed to vary depending on the pump power used. We found that the highest pulse peak power was obtained at the frequency detuning threshold at which the operation changed from the mode-locking to the Q-switched mode-locking regime.

Diode-pumped passively Q-switched and mode-locked Nd:Lu0.15Y0.85VO4 laser with a GaAs saturable absorber

By using a-cut Nd:Lu0.15Y0.85VO4 mixed crystal as laser gain medium, a diode-pumped passively Q-switched and mode-locked (QML) laser with a GaAs saturable absorber in a Z-type folded cavity is demonstrated for the first time. The Q-switched mode-locked laser pulses with about 90% modulation depth are obtained as long as the pump power reached the oscillation threshold. The repetition rate of the passively Q-switched pulse envelope ranges from 50 to 186 kHz as the pump power increases from 0.915 to 6.520 W. Under an incident pump power of 6.52 W, the QML pulses with the largest average output power of 694 mW, the shortest pulse width of 200 ns and the highest pulse energy of 3.73 μJ are obtained. The mode-locked pulse width inside the Q-switched envelope is estimated to be about 275 ps. The experimental results show that Nd:Lu0.15Y0.85VO4 is a promising mixed crystal for QML laser.

Passively Q-switched mode-locking Erbium-doped fiber laser with net-normal dispersion using nonlinear polarization rotation technique

We experimentally demonstrate a passively Q-switched mode-locking (QML) operation in an Erbium-doped fiber ring laser with net normal dispersion by using nonlinear polarization rotation technique. A 2 m long section of dispersion compensating fiber (DCF) with extra large positive dispersion was inserted into the cavity to ensure the fiber laser working in the region of net positive dispersion. By carefully adjusting the polarization controller, both uniform dissipative mode-locking pulses with fundamental repetition rate and QML pulse trains with tunable repetition rate from 71.58 to 98.83 kHz are achieved. It is found that the QML operation is caused by the interaction between the polarization state of the pulse and the intracavity polarizer.

Compact and efficient Kerr-lens mode-locked diode-pumped actively Q-switched YVO 4–Nd:YVO 4 laser

By using a simple linear configuration, a stable and efficient YVO 4–Nd:YVO 4 laser, actively Q-switched by an acousto-optic modulator and passively mode-locked by KLM is realized, from which the great average output power, the high efficiency are obtained and the mode-locked pulse inside the Q-switched pulse has a repetition rate of 470 MHz. The nearly 100% modulation depth of the Q-switched mode-locked pulses can be obtained at any pump power over the threshold. Considering the Kerr-lens effect of laser medium and Q-switching by an acousto-optic modulator, we have analyzed the self-mode-locked YVO 4–Nd:YVO 4 laser by using the nonlinear ABCD propagation matrix and the hyperbolic fluctuation mechanism. The numerical solutions are in good agreement with the experimental results.

Diode-pumped doubly Q-switched mode-locked YVO 4/Nd:YVO 4 laser with AO and GaAs saturable absorber

By using both acousto-optic (AO) modulator and GaAs saturable absorber, a diode-pumped doubly Q-switched and mode-locked (QML) YVO 4/Nd:YVO 4 laser is presented. The average output power and the pulse width of the Q-switched envelope have been measured. The Q-switch pulse energy of the doubly QML laser are higher than that only with GaAs. The stability of the QML laser with the dual-loss-modulation is significantly improved if compared to that only with GaAs.The experimental results show that the doubly QML YVO 4/Nd:YVO 4 laser has nearly 80% modulation depth and deeper than that of the singly passively QML pulse. The doubly Q-switched mode-locked pulse inside the Q-switched envelope has a repetition rate of 111 MHz and its pulse width is estimated to be about 700 ps. By using a hyperbolic secant square function and considering the Gaussian distribution of the intracavity photon density, the coupled equations for diode-pumped dual-loss-modulated QML laser is given and the numerical solutions of the equations are in good agreement with the experimental results.

Injection Mode-Locked, Q-Switched Nd:YAG Laser at 1319 nm

There is currently no laser source that can provide both efficient excitation of mesospheric sodium and allow removal of the effects of guide-star elongation, as required for multi-conjugate adaptive optics in next-generation extremely large telescopes. We describe a Q-switched 1319 nm Nd:YAG laser that is mode-locked by injecting a short pulse into the Q-switched laser. It produces Q-switched mode-locked pulses that are synchronized to an external source. We also discuss how such pulses at 1064 nm and 1319 nm can be used to generate pulsed sodium-resonant guide stars via sum frequency generation, and thus satisfy the above requirements.

Diode-pumped passively Q-switched mode-locking Nd:Y0.5Gd0.5VO4 laser at 1.34 μm with Co2+:LaMgAl11O19 saturable absorber

We reporte a passively Q-switched and mode-locked Nd:Y0.5Gd0.5VO4 laser at 1.34 μm with Co2+:LaMgAl11O19(Co:LMA) crystal as the saturable absorber. With the incident pump power of 6.56 W, a maximum output power of 242 mW was obtained. Q-switched mode-locking pulses with modulation depth nearly 100% were obtained. The width of the mode-locked pulse was estimated to be less than 600 ps.

High-power passively Q-switched mode-locking Nd:GdVO4 laser with LT-InGaAs saturable absorber

The generation of passively Q-switched mode-locking (QML) pulse has been obtained from a diode-pumped Nd:GdVO4 laser with a LT-InGaAs wafer as saturable absorber as well as output coupler. Under the incident pump power of 10 W, an average output power of QML was 1.8 W with a Q-switched repetition rate of 280 kHz. The pulse duration of Q-switched pulse is about 160 ns and mode-locked pulse within the Q-switched envelope had a repetition rate of 410 MHz. It is indicated that the present LT-InGaAs is a very promising device in the field of mode locking solid-state laser, and we are sure that it will be complete pure cw mode locking with single beam output easily after further optimizing in the parameter such as saturation fluence, modulation depth, recovery time and damage threshold in semiconductors.

Stable Q-switched mode-locked Nd3+:LuVO4 laser by Cr4+:YAG crystal

In use of saturable Cr(4+):YAG crystals, we have demonstrated the stable Q-switched and mode-locked (QML) operation of the Nd:LuVO(4) laser. The operation range of QML in use of the Cr(4+):YAG is larger than that use of SESAM and NLM. The obtained shape of Q-switched envelope, repetition rate and pulse energy are demonstrated to depend on the initial transmittance of the Cr(4+):YAG and reflectivity of the output coupler. Using R = 60% and T(0) = 40%, the highest pulse energy of 77 microJ of each Q-switched envelope, and the highest peak power about 200 kW of Q-switched mode-locked pulses can be obtained at 15 W pump power. It demonstrate the superior characteristic of the Nd:LuVO(4) crystal.

Efficient Laser-Diode End-Pumped Passively Q-Switched Mode-Locked Yb:LYSO Laser Based on SESAM

We report an efficient Q-switched laser action based on a semiconductor saturable absorber mirrors (SESAMs) as passively Q-switched laser starter and a Yb:LYSO alloyed crystal as gain material pumped directly by 974 nm In GaAs laser diodes. The output pulse duration is measured to be about 7μs, while the average power and the repetition rate of the pulse chain are about 0.92 W and 6.2kHz, respectively, under 12.5 W absorbed pumping power. The Q-switched mode-locked pulse train is also observed in this setup. The laser performance shows that Yb:LYSO is a promising laser gain medium for laser-diode pumped compact solid-state lasers.

Diode-pumped passively Q-switched mode-locked Nd:YLF laser with uncoated GaAs saturable absorber

We have demonstrated passively Q-switched mode-locked all-solid-state Nd:YLF laser with an uncoated GaAs wafer as saturable absorber and output mirror simultaneously. Q-switched mode-locking pulses laser with about 100% modulation depth were obtained. The average output power is 890mW at the incident pump power of 5.76W, corresponding to an optical slop efficiency of 20%. The temporal duration of mode-locked pulses was about 21ps. At the Q-switched repetition rate of 30kHz, the energy and peak power of a single pulse near the maximum of the Q-switched envelope was estimated to be about 1.6μJ and 76kW.

Q-switched mode locking with acousto-optic modulator in a diode-pumped Nd:YVO4 laser

The Q-Switched Mode Locking (QML) regime provides the generation of relatively high peak power picosecond pulses train with energies of a few muJ each in a simple resonator. The fully modulated efficient QML regime was demonstrated in the diode-pumped Nd:YVO4 laser. The acousto-optic cell playing a double role of Q-switch and Mode Locker was located near flat output coupler. The two folding mirrors were mounted on the translation stages for matching the resonance frequency of the cavity to the radio frequency of acousto-optic modulator. The QML pulses with envelope durations of 100-150 ns and near 100% modulation depth were observed for wide range of pump powers and repetition rates. Up to 3 W of output average power, 100 muJ of the envelope energy, having approximately 5-8 mode-locked pulses were achieved.

Characterization of laser-diode end-pumped intracavity frequency doubled, passively Q-switched and mode-locked Nd:YVO 4 laser

Simultaneous Q-switching and mode-locking in a laser-diode end-pumped intracavity frequency doubled Nd:YVO 4/KTP green laser using Cr 4+:YAG saturable absorber is experimentally demonstrated. The influence of the initial transmission ( T 0) of the Cr 4+:YAG crystal on the Q-switched mode-locked green pulses as well as on the average green power is characterized by using Cr 4+:YAG crystal with various T 0. The effect of T 0 on the pulse build-up time in intracavity second harmonic configuration is theoretically investigated. It was found that the depth of modulation for the mode-locked pulses is greatly improved at the second harmonic wavelength as compared to that for the fundamental wavelength. The average pulse duration of the individual mode-locked pulse for the second harmonic beam measured to be less than 500 ps with a repetition rate of 400 MHz .

All-solid-state passively Q-switched mode-locked Nd-doped fiber laser

We report the generation of Q-switched mode-locked pulses from a Nd-doped fiber laser that uses a solid-state solution of BDN-I dye as the saturable absorber and is pumped by a GaAlAs laser diode. For an absorbed pump power of 110 mW, pulses of 8-nsec duration at a repetition rate of 14 MHz can be generated under an 800-nsec-wide Q-switched envelope at a repetition rate of 10 kHz, yielding an average output power of 8 mW near 1.06 μm. This corresponds to approximately 9 W of peak power in the main mode-locked pulse.

Pulsed laser damage thresholds and laser treatment energy parameters, in vivo, of human aphakic intraocular membranes.

Energy and power density damage thresholds were determined for the perforation of human aphakic pupillary membranes and intraocular lens implants, in vivo, at the focal point of Neodymium-YAG ophthalmic laser systems, at 1,064 nm, which produced Q-switched nanosecond pulses (TEMoo, pulse duration; 20 ns) and mode-locked pulse trains (TEMoo, 9-11 pulses, pulse duration; 30 ps, entire pulse train delivered in 50-70 ns). Pulse energies bracketing the damage thresholds and focal diameter were tabulated. The energy density and power density thresholds for perforation of the pupillary membranes (hereafter referred to as perforation threshold) were slightly lower and power density damage thresholds higher for shorter duration pulses, eg--66 J/cm2 (2,200 GW/cm2) with the picosecond pulse trains vs 80 J/cm2 (2.7 GW/cm2) with the nanosecond pulses and were similar in pseudophakics and aphakics; 78 J/cm2 for pseudophakics vs 83 J/cm2 aphakics, both treated with single nanosecond Nd-YAG pulses, and 68 J/cm2 for pseudophakic vs 66 J/cm2 for aphakic patients treated with picosecond Nd-YAG laser pulse trains. The number of laser pulses and pulse energies required for successful discussion of the pupillary membranes depended not only on the pulse parameters but also on the characteristics of the membrane, such as thickness, nonuniformity, capsular haze, or capsular haze combined with fibrosis.

High performance avalanche transistor switchout for external pulse selection at 106 μm

The design and performance of an avalanche transistor switchout are described. The device selects a single pulse from a train of cw or Q-switched mode-locked pulses and introduces less than +/-1% amplitude variation in the selected pulse. The prepulse rejection ratio exceeds 10(7), and a lifetime of greater than 10(7) shots has been achieved.