Single Q-switched Pulse Research Articles

All fibre Q-switched Thulium-doped fibre laser incorporating Thulium–Holmium co-doped fibre as a saturable absorber

A novel all fibre Q-switched Thulium-doped fibre laser (TDFL) is reported which includes a short length of a Thulium–Holmiumco-doped fibre (THDF) as a saturable absorber. A high repetition rate (27.26 kHz) coupled with a low pulse width (19.06μs) is obtained for single wavelength Q-switched pulse operation at an output wavelength of 1911.5 nm using a pump power of 200 mW. Increasing the pump power from 200 mW to 700 mW results in the repetition rate increasing from 27.26 kHz to 99.67 kHz and the pulse width decreasing from 19.06μs to 920 ns. The centre wavelength of the single Q-switched pulse was also red shifted from 1911.5 nm to 1932.5 nm with increasing the pump power. A 45 m length single-mode fibre (SMF-28) provided dispersion compensation, and effectively an SMF-THDF-SMF structure is inserted in the cavity which operates in a similar manner to an SMF-MMF-SMF structure, providing a strong multimode interference effect which supports dual-wavelength operation. A stable dual-wavelength Q-switched pulse was achieved at a threshold pump power of 213 mW. The dual-wavelength Q-switched pulse operation was generated at 1911.5 nm and 1914.5 nm with a repetition rate of 8.45 kHz and pulse width of 20.02μs. The dual-wavelength spacing of this pulse operation was 3 nm, which was in good agreement with calculations based on the multimode interference effect induced by the THDF. The repetition rate increased from 8.45 kHz to 70.65 kHz and the pulse width decreased from 20.02μs to 870 ns with increasing pump power. At the maximum pump power of 700 mW, the maximum output power was measured as 27.4 mW. The experimental results confirm that the THDF can be utilized as a SA to generate a stable and tunable single-wavelength Q-switched pulse output as well as dual-wavelength Q-switched pulse in the 2.0μm wavelength region.

Q-switched and mode-locked Er-doped fiber laser using PtSe2 as a saturable absorber

We report a passively Q-switched and mode-locked erbium-doped fiber laser (EDFL) based on PtSe2, a new two-dimensional material, as a saturable absorber (SA). Self-started Q-switching at 1560 nm in the EDFL was achieved at a threshold pump power of 65 mW, and at the maximum pump power of 450 mW, the maximum single Q-switched pulse energy is 143.2 nJ. Due to the polarization-dependent characteristics of the PtSe2-based SA, the laser can be switched from the Q-switched state to the mode-locked state by adjusting the polarization state. A mode-locked pulse train with a repetition rate of 23.3 MHz and a pulse width of 1.02 ps can be generated when the pump power increases to about 80 mW, and the stable mode-locked state is maintained until the pump power reaches its maximum 450 mW. The maximum single mode-locked pulse energy is 0.53 nJ. This is the first time to our knowledge that successful generation of stable Q-switched and mode-locked pulses in an Er-doped fiber laser has been obtained by using PtSe2 as a saturable absorber.

Tunable, Q-switched Tm,Ho:LLF laser with a conductively cooled triangular prism rod

We have developed a conductively cooled, Q-switched 2 μm laser with a triangular-prism Tm,Ho:LLF rod. Using a fused-silica acousto-optic Q-switch, the laser produced an output energy of 30 mJ in a single Q-switched pulse at a pulse repetition frequency of 5 Hz. Although the laser rod had polished lateral surfaces, no parasitic oscillation occurred, even at the maximum pumping level. In addition, broadly tunable laser performance was achieved with a birefringent filter plate under relatively large output coupling. The laser could be continuously tuned from 2051 to 2069 nm. Measured tuning characteristics were in reasonable agreement with calculated results.

Pulse characteristics of passively Q-switched 1.34 μm Nd:GdVO4/Co2+:MgAl2O4 laser

Passively Q-switched output of a diode-pumped 1.34 μm Nd:GdVO4 laser was demonstrated by using Co2+:MgAl2O4(Co2+:MALO) crystal as the saturable absorber for the first time. When the transmission of output mirror is 15%, the Q-switched pulse width is 110 ns and a corresponding average output power is 460 mW under the pump power of 9.69 W. The optical-optical conversion efficiency is 36%. At about 330 kHz repetition rate, the single Q-switched pulse energy and the peak power are about 1.39 μJ and 12.6 W, respectively.

Diode-pumped passively Q-switched and mode-locked Nd:GGG laser at 1.3 μm with V3+:YAG saturable absorber

Using V3+:YAG crystal as the saturable absorber, a diode-pumped passively Q-switched and mode-locked Nd:GGG laser operating at 1.3 μm is realized for the first time. The mode-locking modulation depth of nearly 100% has been achieved. The maximum output power and the single Q-switched pulse energy are 410 mW and 8.3 μJ. The mode-locked pulse inside the Q-switched pulse has a repetition rate of 349 MHz, and its average pulse width is estimated to be about 750 ps.

Diode-pumped passively Q-switched Nd:GdVO4 laser at 1342 nm with V:YAG saturable absorber

We have demonstrated an efficient diode-pumped passively Q-switched Nd:GdVO4 laser working at 1342nm by using an uncoated V3+:YAG crystal as the saturable absorber, in which both a-cut and c-cut Nd:GdVO4 crystals are employed. At the maximum absorbed pump power of 9.45W, the maximum average output power can reach 519mW and 441mW corresponding to the output coupler with different transmission of 3% and 10% by using an a-cut Nd:GdVO4 crystal at 1342nm, while the shortest pulse duration could be as low as 21.7ns and 22.3ns with the repetition rate of 48.41kHz and 53.25kHz by using a c-cut Nd:GdVO4 crystal, corresponding to the output coupler with different transmission of 3% and 10% at 1342nm, and the single Q-switched pulse energy are 6.67uJ and 7.06uJ, the pulse peak power are 307W and 316W, respectively. The experimental results show that c-cut Nd:GdVO4 laser can generate shorter pulse with higher peak power in comparison with a-cut one.

Co2+:LMA crystal as saturable absorber for a diode-pumped passively Q-switched Nd:YVO4 laser at 1342 nm

We have demonstrated an efficient diode-pumped passively Q-switched Nd:YVO4 laser at 1342 nm by using an uncoated Co2+:LaMgAl11O19 (Co2+:LMA) crystal as the saturable absorber. With the absorbed pump power of 11.7 W, the pulse width could be as low as 42 ns, with a corresponding average output power of 580 mW. At around 40 kHz repetition rate, the energy of a single Q-switched pulse was estimated to be about 14.5 μJ and the peak power was 346 W. The passive Q switching operation for the Co2+:LMA in different polarization states was also investigated.

Passively Q-switched and mode-locked diode-pumped Nd:YVO4 laser with LT-GaAs output coupler

We have demonstrated an efficient and compact passively Q-switched and mode-locked (QML) 1064nm Nd:YVO4 laser by using a low temperature grown GaAs (LT-GaAs) saturable absorber as well as an output coupler. Stable QML with envelope duration as short as 10ns and Q-switched repetition rate of 36kHz was obtained. It is the shortest envelope duration as far as we know, and it is so short that it can be used as Q-switching pulses directly. At 6.9W of the incident pump power, average output power of 1.24W was achieved and the corresponding peak power and energy of a single Q-switched pulse were 3.44kW and 34.4μJ, respectively. The mode-locked pulses inside the Q-switched pulse envelope had a repetition rate of 780MHz.

Growth and Q-switching performance on mixed laser crystal Nd 0.0055(Gd 0.64Y 0.36) 0.9945VO 4

A Nd 0.0055(Gd 0.64Y 0.36) 0.9945VO 4 mixed laser crystal has been successfully grown by the Czochralski method. Properties of this crystal have been introduced. Formed with a simple concave-plano resonator, passive Q-switching operation of a diode-pumped Nd 0.0055(Gd 0.64Y 0.36) 0.9945VO 4 laser with Cr 4+:YAG has been demonstrated. For the Q-switched operation, the maximum average power was measured to be 1.11 W with a corresponding pulse repetition rate of 10 kHz and a Q-switched pulse duration of 7.6 ns. The largest single Q-switched pulse energy of 111 μJ and the highest peak power of 14.61 kW have been obtained in the laser.

Passive Q-switching characteristics of Yb3+:Gd3Ga5O12 crystal

The passively Q-switched laser characteristics of a quasi-three level Yb3+:Gd3Ga5O12 (Yb3+:GGG) crystal with Cr4+:YAG saturable absorbers are studied experimentally and theoretically. The pulse parameters under different experimental conditions are measured. Some characteristics different from those of a four-level system are found. In the theoretical aspect, taking into account the spatial distributions of the pump light and intracavity laser mode, the rate equations describing the single Q-switched pulse characteristics of a quasi-three-level system are obtained. The obtained theoretical results are in fair agreement with the experimental results. Some topics such as the influence of the pumping power, the selection of the pump beam size, the optimal combination of output coupler reflectivity and saturable absorber initial transmission, the influence of the excited absorption of the saturable absorber, are discussed.

Passively Q-switched operation of a double contact tapered InGaAs/GaAs diode laser

High power picosecond pulse generation from a two-contact tapered two quantum well 980 nm InGaAs/GaAs diode laser is investigated using a passive Q-switching technique for the first time. Tail-free and single peak Q-switched pulses are obtained by applying reverse bias voltages in the range of 0 to −9 V to the absorber section of the device. Optical pulses with 41 ps (down to 29 ps) durations and peak powers in excess of 1.5 W are obtained in a well-defined single lobed far-field. Such an improvement in the optical pulses is attributed to a reduction of absorber recovery time.

Narrow-linewidth operation of a compact THz-wave parametric generator system

We developed a compact THz-wave parametric generator (TPG) system with a diode-pumped Nd:YAG laser that was specially designed for pumping the TPG. The pump laser produced an output energy of 11 mJ in a single Q-switched pulse with a pulse width of 6 ns. Using MgO:LiNbO 3 crystals, a THz-wave energy of 1.7 pJ was obtained in unseeded operation, and a broad THz-wave spectrum (1.4–2.2 THz) was then observed. Furthermore, a narrow THz-wave linewidth of less than 33 GHz was achieved by injection seeding of the idler wave. The THz-wave energy was increased by a factor of 3 compared to the unseeded output.

Tabletop terahertz-wave parametric generator using a compact, diode-pumped Nd:YAG laser

We specifically developed a diode-pumped, Q-switched Nd:YAG laser to act as a pump source for a terahertz-wave parametric generator. A single Q-switched laser pulse (pulse width 12 ns, pulse repetition frequency 40 Hz) produced an output energy of 12 mJ. Utilizing this pump source, we were able to construct a compact (650×350 mm) terahertz-wave parametric generator using LiNbO3 crystals. We achieved a broad terahertz-wave spectrum, ranging from 1.2 to 2.4 THz, with a pump energy of 12 mJ.

Pulsed fiber laser using micro-electro-mechanical mirrors

Two different types of micromirrors are integrated with a fiber laser to modulate the cavity Q-factor. Both systems operate at frequencies up to 60 kHz and generate a pulse peak power 100 times higher than the continuous emission. We simulate the emitted pulses and find a good agreement with the measured value for the period of relaxation oscillations. The simulations also show the necessity of a shorter rise time of the Q-factor modulation to achieve one single giant and narrow Q-switched pulse.

Short pulse generation in a Nd:YAG laser by silicon

A novel passive Q-switching technique using silicon is demonstrated. A single Q-switched pulse with a maximum energy of 3 mJ and 18 ns duration in a Nd:YAG laser was obtained. A theoretical model that describes the short pulse generation dynamics based on the change of refractive index of silicon due to lattice temperature increase and free-carrier production is presented. Experimental results have confirmed our theoretical model.

Eyesafe Lasers and Their Applications. Characteristics for Normal Mode and Q-Switched Operations of Flashlamp-Pumped Cr,Tm(,Ho): YAG Lasers.

We have demonstrated normal mode and Q-switched operations of flashlamp pumped Cr, Tm (, Ho):YAG lasers. When operation in the normal mode, output energies of 2.3 J and a slope efficiency of 2 % have been achieved, and the thermal lensing has been observed in the laser rod at the high repetition rate. In addition, the TEM00 mode single Q-switched pulse with a pulse energy of 54 mJ and a pulse width of 206 ns was obtained by using a fused silica AO Q-switch as a mode selector. The comparison of Q-switched operations employing a LiNbO3 Pockels cell and the AO Q-switch is also described.

Ho:CaF_2 solid-state saturable-absorber Q switch for the 2-μm Tm,Cr:Y_3Al_5O_12 laser

The holmium-doped calcium fluoride (Ho:CaF(2)) crystal was shown to be an effective solid-state saturable-absorber Q-switch for a flash-lamp-pumped Tm,Cr:Y(3)Al(5)O(12) laser at 2.017 µm. With a 1-cm-thick Ho(0.5%),Er(5%):CaP(2) saturable absorber and a 6.3% output coupler, a single Q-switched laser pulse of 51 mJ in energy and 60 ns in duration was obtained at a flash-lamp input energy of 85 J. With a 14.6% output coupler, a typical Q-switched laser pulse of 84 mJ and 82 ns was observed.

Ho:YVO_4 solid-state saturable-absorber Q switch for a 2-μm Tm, Cr:Y_3Al_5O_12 laser

The holmium-doped yttrium orthovanadate (Ho:YVO4) crystal was shown to be an effective solid-state saturable-absorber Q switch for a flash-lamp-pumped Tm,Cr:Y3Al5O12 laser operating at 2.017 μm. A single Q-switched laser pulse of 3.5 mJ in energy and 45 ns in duration was observed with a 1-mm-thick 4% Ho:YVO4 solid-state saturable absorber, which was grown with the high-temperature-solution-growth method.

Passive Q switching of the alexandrite laser with a Cr4+:Y2SiO5 solid-state saturable absorber

Passive Q switching of a flashlamp-pumped alexandrite laser with a Cr4+:Y2SiO5 (Cr4+:YSO) solid-state saturable absorber has been demonstrated at room temperature. An output of a single Q-switched laser pulse of 20 mJ in energy and 70 ns in duration was obtained. The output wavelength of the Q-switched laser pulse and the free-running laser was 753 nm.

Diode-pumped long-pulse-length Ho:Tm:YLiF_4 laser at 10 Hz

An optical efficiency of 0.052 under normal mode operation for diode-pumped Ho:Tm:YLiF(4) at a pulse repetition frequency of 10 Hz has been achieved. Laser output energy of 30 mJ in single Q-switched pulses with 600-ns pulse length were obtained for an input energy of 3 J. A diffusion-bonded birefringent laser rod consisting of Ho:Tm-doped and undoped pieces of YLF was utilized for 10-Hz operation.