Saturable absorber Q- and gain-switched all-Yb3+ all-fiber laser at 976 and 1064 nm

All-fiber passively Q-switched Tm-doped laser with a mode field area mismatched Tm-doped saturable absorber

We demonstrate a high peak power, all-fiber passively Q-switched Tm-doped laser operating at 1940 nm for applications in soft tissue ablation. High peak power and passive Q-switching were achieved via a clad pumped gain fiber and a smaller core Tm-doped fiber saturable absorber respectively. Clad pumping was achieved via two 30 W diodes operating at 793 nm. At 50.7 W of pump power, laser pulses with 140 ns FWHM duration and average power of 14.5 W were obtained at a repetition rate of 328 kHz which corresponded to a pulse energy of ~44 µJ and a peak power of ~316 W. The laser had a narrow 0.14 nm linewidth at the maximum output power. The laser was used to cut chicken breast as well as ovine cortical and subcortical brain tissues and average ablation efficiencies of 29, 40 and 42% were obtained, respectively. Cutting speeds of 10 mm/s for ovine brain tissue and 5 mm/s for chicken breast were achieved. Further resection experiments were performed with the target tissue placed under a thin layer of water. A resected volume with length, width and depth of 5 mm, 2.5 mm, and 2.8 mm were obtained, corresponding to a resection rate of ~0.58 mm3/s. To our best knowledge, this is the first report of an all-fiber clad-pumped passively Q-switched Tm-doped fiber laser with a core mismatched saturable absorber being used for tissue ablation experiments.

Demonstration of a 700 W × 2 ports single-stage all-fiber nanosecond amplifier seeded by a multi-cavity passively Q-switched laser

We demonstrate a single-stage all-fiber nanosecond amplifier with a total average power of greater than 1.4 kW by employing what we believe to be a novel multi-cavity passively Q-switched fiber laser as the seed laser. The multi-cavity seed laser adopts a piece of Yb-doped fiber (YDF) as saturable absorber (SA), and it includes two external cavities resonating at 1030 nm and an internal cavity working at 1064 nm, respectively. Using such a scheme, a stable dual-channel laser output with a total average power of >35 W, a pulse width of 45 ns, and an optical conversion efficiency of 72% operating at 1064 nm is achieved. By power scaling the multi-cavity seed laser, a dual-channel single-stage nanosecond amplifier is obtained with a single-port average power of exceeding 700 W and a pulse energy of about 7.3 mJ. To the best of our knowledge, this work is the highest average power and optical conversion efficiency for passively Q-switched all-fiber laser employing SA fiber, and the highest average power for a single-stage all-fiber nanosecond amplifier.

Simulation for efficiency improvement of a thuilium Q-switched ytterbium-doped all-fiber laser

We theoretically explore the mechanism in a thulium Q-switched ytterbium-doped all-fiber fiber laser using a set of rate equations to model the correlations between the photons and the five energy levels of thulium involved in the Q switching mechanism. We demonstrate that by coupling with a gain-switched resonator, the Q-switched laser is stabilized up to the maximum pulsing rate that is limited by the lifetime of level ³H₅. To the best of our knowledge, this is the first study that revealed that level ³H₅ plays an essential role in reinitialization, achieving sequential pulses, and limiting the maximum repetition rate.

Simultaneous dual-wavelength pulses achieved by mixing spiking and passive Q-switching in a pulsed Nd:GdVO4 laser with a Cr4+:YAG saturable absorber

A method for generating a dual-wavelength, dual pulse Nd:GdVO₄ laser at 1.06 μm (F_3/24→I_11/24) and 1.34 μm (F_3/24→I_13/24) is proposed. When the 1.34-μm spiking threshold is less than the 1.06-μm Q-switched threshold, the generation of a 1.34-μm spiking pulse leads to a 1.06 μm Q-switched pulse, resulting in a dual-wavelength laser. With a pump power of 11 W, the pulse widths are 89.5 and 427.8 ns for 1.06 and 1.34 μm, respectively, with a 36.5-KHz repetition frequency.

1590-nm-pumped passively Q-switched thulium all-fiber laser at 1900 nm

We propose and demonstrate a passively Q-switched 1900-nm thulium all-fiber laser using the mode-field-area mismatch method. A thulium fiber laser was core-pumped at 1590 nm and saturable-absorber Q-switched at 1900 nm through the use of a thulium saturable absorber fiber that had a relatively smaller mode field area than the gain medium. Sequential pulsing with a pulse energy of 12 μJ and a pulse duration of 160 ns was obtained. The pulse repetition rate was increased linearly with the applied pump power. With a pump power of 4.5 W, an average output power of 0.61 W and a pulse repetition rate of 50.7 kHz were achieved.

Short pulsed gain-switched fiber laser with improved efficiency utilizing unabsorbed pump recovery

A simple solution for increasing the slope efficiency of a gain-switched fiber laser based on Yb-doped active fiber is presented. By adding a fiber amplifier stage, which recovers the unabsorbed pump light from the gain-switched oscillator, a significant increase in slope efficiency is achieved. The pulses at 1030-nm wavelength have an FWHM of 28 ns and a peak power of 2.3 kW.

Single stage Yb-doped fiber laser based on gain switching with short pulse duration

A simple solution for producing nanosecond laser pulses can be obtained using gain-switched fiber lasers. In this paper, we present an optimized single stage gain-switched ytterbium-doped fiber laser. Three fiber lengths were tested to show the impact of length on the laser output pulse. A pulse as short as 28 ns at 1.4 kW peak power and a maximum peak power of nearly 2 kW at 41 ns pulse duration was achieved. The laser possess a linear polarized output, very good beam quality of M2 < 1.1, and a spectral bandwidth of 0.11 nm.

Hybrid-pumped, gain-switched 1120 nm ytterbium-doped fiber laser

A monolithic, hybrid-pumped, gain-switched, single-mode, 1120 nm Yb-doped fiber laser is reported. Pumped by a 1064 nm pulse fiber source and a continuous-wave 976 nm laser diode, a record output pulse energy of 91.7 μJ at repetition rate of 10 kHz is obtained. The full width at half-maximum of the pulses is 4.1 μs, and the slope efficiency corresponding to the 1064 nm laser is more than 46%. The pulse build-up time and a pulsewidth decrease with an increase in the pump pulse energy are observed. In the gain-switched pulses, mode-lock-resembling pulses are detected. The subpulse's duration is about 415 ns, including the cavity round-trip time, and the width varied from 80 to 320 ns, which is longer than the traditional mode-locked laser.

Stable passively Q-switched and gain-switched Yb-doped all-fiber laser based on a dual-cavity with fiber Bragg gratings

We demonstrate a stable passively Q-switched and gain-switched Yb-doped all-fiber laser cladding-pumped by a continuous fiber-coupled 976 nm laser diode. By use of an all-fiber dual-cavity, the efficient elements of the laser mainly include the fiber Bragg gratings and rare-earth doped fiber, allowing the oscillator to be integrated in a compact size with reliable and stable output. In this scheme, an efficient laser output with 45 ns pulse width, 62 μJ pulse energy, and 1.4 kW peak power operating at 1081 nm was obtained. To the best of our knowledge, this is the minimum pulse width in this similar kind of all-fiber configuration at present. Sequential nanosecond pulses were obtained at the repetition rate of several to tens of kHz with the variation of the diode pumping power. Effects of laser parameters such as pump power, cavity length, external-cavity wavelength, and FBG reflectivity on laser performance were also presented and discussed.

All-fiber passively Q-switched fiber laser with a Sm-doped fiber saturable absorber

We demonstrate an all-fiber passively Q-switched Yb-doped laser using a piece of Sm-doped fiber as a saturable absorber. The laser was pumped by two 25W, 975 nm fiber coupled diodes and Q-switching was initiated when the ASE generated in the core of the gain fiber bleached the Sm-doped saturable absorber. The laser produced 1064 nm pulses with 28 μJ pulse energy and a 200 ns pulse width at a repetition rate of 100 kHz. The pulse energy and peak power are an order of magnitude higher than what previous reported which was also in all-fiber configuration. Effects of laser parameters, such as Sm-fiber length, pump power and duration on laser performance were presented and discussed. Stable Q-switched pulses were obtained at the repetition rate varying from 10 kHz to 100 kHz, which makes this laser suitable for different applications.

Lensless intracavity focusing in a passively Q-switched all-fiber laser using the mode-field-area mismatch

Intense lensless intracavity focusing in a saturable absorber Q-switched all-fiber laser resonator by use of loss arrangement and mode-field-area mismatch between the fibers is investigated for the first time. The intracavity power distribution was related to the locations and values of the cavity losses as the saturable absorption loss, the reflection loss of the output coupler, and the splicing loss between the gain fiber and the absorber fiber. With a mode-field-area mismatch and a reduced splicing loss with the gain fiber, a power density in the absorber fiber was achieved that was 11.9 times higher than that in the gain fiber.

High-power all-fiber passively Q-switched laser using a doped fiber as a saturable absorber: numerical simulations

We report a design for a power-scalable all-fiber passively Q-switched laser that uses a large mode area Yb-doped fiber as a gain medium adiabatically tapered to an unpumped single-mode Yb-doped fiber, which serves as a saturable absorber. Through the use of a comprehensive numerical simulator, we demonstrate a passively Q-switched 1030 nm pulsed laser with 14 ns pulse duration and 0.5 mJ pulse energy operating at 200 kHz repetition rate. The proposed configuration has a potential for orders of magnitude of improvement in both the pulse energies and durations compared to the previously reported result. The key mechanism for this improvement relates to the ratio of the core areas between the pumped inverted large mode area gain fiber and the unpumped doped single-mode fiber.

Experimental investigation of relative timing jitter in passively synchronized Q-switched lasers

Relative timing jitter between synchronized Q-switched lasers, or lack thereof, is important for stable sum-frequency generation. Experimental investigation of two passively synchronized lasers shows that the jitter is minimized when the free-running repetition rates of the two lasers are close to, but not exactly, matching. When the free-running repetition rates are matched, the jitter is significantly large. At the best operating point, the pulse-to-pulse period was 200 μs, while the relative jitter between the two lasers was 9 ns. If the effect of the master laser's pulse-to-pulse jitter is removed, the residual timing jitter between the two lasers was 6 ns, which corresponds to the lower limit set by pump power fluctuations and noise from spontaneous emission.