Passive Q-switching Research Articles

Bismuth functionalized GaAs as saturable absorber for passive Q-switching at 1.34 μm

First principles simulations showed bismuth doped GaAs could modify the electronic band structure. Hereby, Bi:GaAs exhibited excellent nonlinear absorption properties at 1.3 μm with a modulation depth of 6.2%, larger than that of pure GaAs. Subsequently, the passively Q-switched Nd:YVO4 lasers were demonstrated at 1.34 μm with Bi:GaAs and GaAs the saturable absorbers. Stable pulses with the shortest duration of 64 ns at a repetition rate of 138 kHz were generated with Bi:GaAs saturable absorber. In the meantime, we also observed Bi ion doping accelerates the free-carrier recovery, indicating Bi:GaAs excellent candidant for 1.3 μm pulse generation.

Frequency expansion of efficient passively Q-switched orthogonally-polarized dual-wavelength laser

We report on the frequency expansion of efficient passively Q-switched (PQS) orthogonally-polarized dual-wavelength laser for the first time, to our knowledge. The dynamic of pulse synchronization for the PQS dual-wavelength laser was analyzed theoretically. With two Nd:YLF crystals, the simultaneous PQS orthogonally-polarized dual-wavelength laser at 1047 and 1053 nm was obtained with the maximum output powers of 4.5 and 4.2 W, respectively, resulting in a total optical-to-optical conversion efficiency of 18.7%. The timing jitter between the 1047 nm main pulse and 1053 nm main pulse was 26.6 ns. Furthermore, substituting one of the Nd:YLF crystals for a Nd:YAG crystal, two sets of simultaneous orthogonally-polarized dual-wavelength lasers at 1047, 1064 nm and 1053, 1064 nm were generated with near 6 W of output power.

Q-switched lasing at the 2 µm wavelength induced by Cu18S nanocrystals

In this paper, we first investigated the nonlinear optical properties of Cu1.8S nanocrystals (NCs) by using Z-scan and balanced twin detector measurement technologies, and then demonstrated a passively Q-switched laser at the 2 µm wavelength. The Cu1.8S NCs were synthesized by a solventless thermolysis method and then mixed with sodium carboxymethylcellulose to form the Cu1.8S NCs film. The film exhibited broadband surface plasmon resonance (SPR) absorption from 800 nm to 2000 nm. By incorporating the Cu1.8S NCs film into a thulium doped fiber laser cavity pumped by a 1570 nm fiber laser, stable passive Q-switching at ∼1975.16 nm was obtained for a threshold pump power of ∼931 mW, and ∼3.4 µs pulse duration with a pulse repetition rate of ∼35.14 kHz was also obtained for a pump power of ∼996 mW. Our results showed that Cu1.8S NCs is a promising saturable absorber (SA) for pulse laser generation at the 2 µm wavelength.

MXene saturable absorber for nanosecond pulse generation in a mid-infrared Ho,Pr:LLF bulk laser

In this paper, high quality few-layer MXene-Ti3C2Tx was fabricated by the LPE method and successfully applied as saturable absorber for a passively Q-switched (PQS) Ho,Pr:LLF laser operating at 2.95 µm. The maximum average output power was determined to be 105 mW with a slope efficiency of 5%. The shortest pulse width and the largest pulse repetition rate were determined to be 266.7 ns and 83.24 kHz, corresponding to the single pulse energy and pulse peak power of 1.26 µJ and 4.73 W, respectively. It is the first demonstration of MXenes applied in mid-infrared (MIR) PQS solid-state bulk lasers, to the best of our knowledge. The results not only verify the broadband nonlinear saturable absorption properties of MXenes, but also pave the way for exploring their applications in photonic devices.

Fluorite-type Tm3+:KY3F10: A promising crystal for watt-level lasers at ∼1.9 μm

Tm3+-doped cubic potassium yttrium fluoride, KY3F10, is a promising laser crystal for efficient watt-level lasers at ∼1.9 μm because of the relatively easy crystal growth by the Czochralski method, advantageous thermo-optical properties, high available Tm3+ doping levels and very efficient cross-relaxation mechanism. A compact diode-pumped 8 at.% Tm3+:KY3F10 laser generated 1.85 W at 1891 nm with a slope efficiency of 65.2% and a laser threshold of 450 mW. A negative thermal lens was detected in this crystal owing to the negative dn/dT coefficient (−8.9 × 10−6 K−1). Passive Q-switching of the Tm3+:KY3F10 laser by single-walled carbon nanotube saturable absorber was demonstrated yielding 13.2 μJ/490 ns pulses at a repetition rate of 58 kHz.

Passive Q-switching using Lead Sulfide suspension as a saturable absorber in 1.5 μm region

We report on Lead Sulfide (PbS) dispersed in sodium dodecyl sulfate (SDS) used as a saturable absorber (SA) in erbium-doped fiber laser (EDFL) ring cavity configuration. It has been fabricated in a suspension form by simple method for flexible usage with high stability. Then, the prepared SA was integrated in the EDFL cavity producing passively Q-switched pulses at wavelength of 1566.3 nm with 3 dB bandwidth of 4.23 nm. Stable short pulses of 8.55–3.43 µs were generated as the corresponding pump power increased from 73 to 300 mW while the repetition rate tuned from 14.86 to 38.71 kHz accordingly. The maximum pulse energy obtained by the present setup was 10.6 nJ at maximum input pump power. The high signal-to-noise ratio (SNR) of proposed PbS-SDS based SA of ~63 dB represents a considerable stable Q-switched EDFL and proves a high prospect to be used in practical photonic applications.

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.

Passively Q-switched diode-pumped Tm, Ho:LuVO4 laser with a black phosphorus saturable absorber**Project supported by the National Natural Science Foundation of China (Grant Nos. 61775053, 51572053, 51777046, and 61705140).

We presented a passively Q-switched (PQS) diode-pumped c-cut Tm, Ho:LuVO4 laser with a black phosphorus saturable absorber for the first time. Under PQS mode, an average output power of 0.86 W and a peak power of 2.32 W were acquired from the Tm, Ho:LuVO4 laser with the pump power of 14.55 W, corresponding to a pulse width of , a pulse repetition rate of 71.84 kHz, and a pulse energy of about .

Efficient 1 µm Laser Emission of Czochralski-Grown Nd:LGSB Single Crystal.

A 5.0-at.% Nd-doped La0.64Gd0.41Sc2.95(BO3)4 (Nd:LGSB) borate laser crystal was successfully grown by the Czochralski method, for the first time to our knowledge. The spectroscopic properties of the grown crystal are discussed and 1 µm laser emission, under end-pumping with a fiber-coupled diode laser at 807 nm, is reported. A c-cut Nd:LGSB medium yielded 1.35 W continuous-wave output power at 0.63 overall optical-to-optical efficiency, with respect to the absorbed pump power, together with the high 0.68 slope efficiency. With an a-cut Nd:LGSB sample, 0.81 W output power at 0.52 optical-to-optical efficiency was obtained. The laser emission performances under quasi-continuous wave pumping are presented as well, for both c-cut and a-cut crystals. Passive Q-switching was investigated with a semiconductor saturable absorber mirror (SESAM). Laser pulses with 2.2 µJ energy and 32.8 ns durations were recorded from a-cut Nd:LGSB. The average output power reached 0.36 W at 1.55 W absorbed pump power. Passive mode-locking with SESAM was achieved in a long Z-type resonator. Ultrashort pulses with 0.19 W average power, 1.63 nJ energy, and 1.43 ps pulse duration, at 118 MHz repetition rate, are demonstrated for the a-cut Nd:LGSB medium.

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.

Sensitive saturable absorber and optical switch of epsilon-near-zero medium

We investigated the nonlinear absorption and optical switching properties of a typical Epsilon-near-zero (ENZ) thin film made of indium tin oxide (ITO) in the near-infrared region. ITO has a low saturable absorption intensity with the advantages of electric field enhancement. The Q-switching performance in the near-infrared region was demonstrated with the ITO as a passive Q-switcher in the bulk lasers for the first time, to the best of our knowledge. This work shows that ENZ materials have promising applications in ultrafast photonics and may be helpful for the development of further nonlinear optoelectronic devices.

Pulsed laser module based on a high-power semiconductor laser for the spectral range 1500 – 1600 nm

A laser source for bleaching passive Q-switches of erbium-ytterbium lasers is developed and studied. The developed and studied compact pulsed module (peak power exceeding 10 W in a pulse with a duration of 1 μs at a wavelength around 1550 nm) is made on the basis of a semiconductor lasers with an ultra-narrow waveguide integrated with a pulsed pump card. To optimise the output laser characteristics, a series resistance was used in the laser pump circuit. The powers of the free-space and fibre-coupled modules at a temperature of 25 °C are 15 and 12 W, respectively, at a pulse shape close to rectangular.

Saturable absorption properties at 1.54 µm of Cr2+:ZnS prepared by thermal diffusion at hot isostatic pressing

Polycrystalline zinc sulfide (ZnS) samples obtained by chemical vapour deposition were doped with Cr2+ ions using hot isostatic pressing (at 100 MPa/1250 °C). Their structure was studied by means of x-ray diffraction, SEM and Raman spectroscopy. The Cr2+:ZnS samples exhibited excellent transparency in the near-IR. Absorption saturation of Cr2+:ZnS is demonstrated at 1.54 µm (5T2(5D) → 5E(5D) transition of Cr2+ ions in tetrahedral sites) for ns-long pulses yielding a saturation fluence of 0.16 ± 0.03 J cm−2. The laser-induced damage threshold is 6.0 ± 0.5 J cm−2. The synthesized polycrystalline Cr2+:ZnS is promising for passive Q-switching of erbium lasers emitting at 1.5–1.7 µm.

Q-switched Dy:ZBLAN fiber lasers beyond 3 μm: comparison of pulse generation using acousto-optic modulation and inkjet-printed black phosphorus

We report high-energy mid-infrared pulse generation by Q-switching of dysprosium-doped fiber lasers for the first time. Two different modulation techniques are demonstrated. Firstly, using active acousto-optic modulation, pulses are produced with up to 12 μJ energy and durations as short as 270 ns, with variable repetition rates from 100 Hz to 20 kHz and central wavelengths tunable from 2.97 to 3.23 μm. Experiments are supported by numerical modeling, identifying routes for improved pulse energies and to avoid multi-pulsing by careful choice of modulator parameters. Secondly, we demonstrate passive Q-switching by fabricating an inkjet-printed black phosphorus saturable absorber, simplifying the cavity and generating 1.0 μJ pulses with 740 ns duration. The performance and relative merits of each modulation approach are then critically discussed. These demonstrations highlight the potential of dysprosium as a versatile gain medium for high-performance pulsed sources beyond 3 μm.

Passive Q-Switched Operation of a c-Cut Tm,Ho:LuVO4 Laser with a Few-Layer WSe2 Saturable Absorber

We demonstrate experimentally a passive Q-switched (PQS) operation of 2 μm c-cut Tm,Ho:LuVO4 laser with a WSe2 saturable absorber (SA) mirror. We obtain an average output power of 500 mW with a pulse width of 3.5 μs at 116.6 kHz and a pump power of 13.03 W. We measure the output wavelengths of the Tm,Ho:LuVO4 laser to be 2,075.8 nm at the continuous-wave (CW) mode operation and 2,056.9 nm at the PQS mode operation. The beam quality factors $$ {M}_x^2 $$ = 1.11 and $$ {M}_y^2 $$ = 1.06 are obtained in the PQS Tm,Ho:LuVO4 laser.

High efficiency nanosecond passively Q-switched 23 µm Tm:YLF laser using a ReSe2-based saturable output coupler

A 785 nm diode-pumped nanosecond passively Q-switched (PQS) 2.3 µm Tm:YLF laser using a ReSe2-based saturable output coupler (SOC) was reported for the first time. The SOC combined the function of a passive Q-switch and output coupler, greatly reducing the additional insertion loss compared with a conventional separate structure. The modulation depth, saturation intensity, and nonsaturable loss for this ReSe2-based SOC were determined to be 1.3%, 1.7 GW/cm2, and 0.2%, respectively. A maximum average output power of 486 mw, a shortest pulse width of 716 ns, and a repetition rate of 5.0 kHz were obtained under the absorbed pump power of 7.21 W. The nanosecond pulses make the diode-pumped compact 2.3 µm thulium solid-state lasers more attractive for practical applications.

Simulation of saturable absorber material length effect on characteristics of Passive Q-switching and Stokes pulses

The effect of saturable absorber material length on characteristics of passive Q-switching and Stokes pulses has been simulated. A software computer program has been based for solving a rate equations model numerically by Rung –Kutta- Fehalberg method. (Nd:GdVO4), (Cr+4:YAG), and Ba(NO3)2 are used as a active medium, saturable absorber material, and Raman medium respectively. The study shows that an decrease in pulse duration for both pulses (passive Q- switching and Stocks) with saturable absorber material length increases. While the energy and the power are increase with saturable absorber material length increases.

Performance of an Yb:LaCa4O(BO3)3 crystal laser at 1.03–1.04 μm passively Q-switched with 2D MoTe2 saturable absorber

The passive Q-switching performance of an Yb:LaCa4O(BO3)3 crystal laser was investigated for the first time to our knowledge. Stable repetitively pulsed laser action was demonstrated with a 2D MoTe2 saturable absorber under high output couplings ranging from 70% up to 95%. A maximum pulsed output power of 2.11 W was produced at a repetition rate of 357 kHz, with a slope efficiency of 32% in terms of incident pump power. The largest pulse energy, minimum pulse duration, and highest peak power achievable were, respectively, 6.6 μJ, 103 ns, and 52.4 W. Our work suggests that this relatively new monoclinic oxyborate crystal may be more advantageous over most of other Yb-ion materials in making high-energy pulsed lasers passively Q-switched with 2D saturable absorbers.

High Stability LED-Pumped Nd:YVO4 Laser with a Cr:YAG for Passive Q-Switching

With improvements in light-emitting diode (LED) performance and a sharp decline in price, a light source with the irradiance of a laser and the cost of an LED is worthy of further study. We demonstrated a LED-pumped Nd:YVO4 laser in quasi-continuous-wave (QCW) and passively Q-switched (PQS) regime. With an incident pump energy of 6.28 mJ (150 μs pulses at 1 Hz), the Nd:YVO4 laser has an energy of 206 μJ at 1064 nm in the QCW regime. The optical conversion efficiency of the system is 4.1%, and the slope efficiency is 9.0%. A pulsed energy of 2.5 μJ was obtained with a duration of 897 ns (FWHM) in the PQS regime, which means the peak power is 2.79 W. The output energy stability is 97.54%.

Large diameter coreless fiber as a saturable absorber for erbium doped fiber laser cavity based on multimode interference

• Easily handling C-band passively Q-switched erbium doped fiber laser nm has been demonstrated. • Easily spliced large core diameter coreless fiber is served as a saturable absorber for Q-switching ignition. • High pulse repetition rate of 73.3–92 KHz without any intra-cavity tuning element has been obtained. • Stable output pulses of SNR of 50 dB is generated. We demonstrated a Q-switched erbium-doped fiber laser (EDFL) based on large diameter coreless fiber without intra-cavity tuning element for the first time. A single mode fiber –coreless fiber –single mode fiber (SNCFS) structure was employed as a passive Q-switcher relies on Kerr nonlinearity associated with multi-mode interference (MMI) effect. By splicing 10 cm of 125 µm in diameter coreless fiber (NCF) between two single mode fibers (SMFs), C-band Q-switched EDFL with 3-dB bandwidth of 0.138 nm was successfully obtained, making it a simple, compact and easily handling modulation device. A stable Q-switched pulses were achieved with a pump threshold of 188 mW. Pulse repetition rate ranges from 73.3 to 92.0 kHz, minimum pulse width of 3.5 µs and maximum energy of 50.9 nJ were recorded.