Compact Linear Cavity Research Articles

Comparison in 2.1 μm laser performances among Tm:YLF laser intra-cavity pumped Ho:YLF, Ho:YAG, and Ho:YAP lasers

We demonstrate lasing properties of the c-cut Ho:YLF, Ho:YAG and c-cut Ho:YAP laser intra-cavity pumped by a σ-polarized Tm:YLF laser within a compact linear cavity. Owing to the weak thermal lens of the YLF-based host media, maximum Ho laser power of 8.63 W at 2063.1 nm, with a slope efficiency of 25.2% and M2 of 1.41 was obtained in the Ho:YLF laser. Besides, maximum output power of 7.45 W at 2122.2 nm and 3.55 W at 2129.5 nm were obtained with the Ho:YAG and Ho:YAP lasers, respectively, with corresponding slope efficiencies of 23.1% and 11.8%.

Switchable and tunable dual-wavelength passively mode-locked fiber laser

We demonstrate a switchable and tunable dual-wavelength passively mode-locked fiber laser in a compact linear cavity. Two cascaded polarization-maintaining fiber Bragg gratings (PM-FBGs) are used as wavelength-selective components, and a semiconductor saturable absorber mirror (SESAM) is used as a mode-locked component. Four kinds of switchable single-wavelength and two kinds of switchable dual-wavelength mode-locked operations are achieved in 1.0-μm band under lower pump power condition. Through temperature control, we obtain the tunable single-wavelength and dual-wavelength mode-locked operations, and the tunable wavelength range is about 0.5 nm when increase the temperature from 25 °C to 80 °C.

High power continuous laser at 461 nm based on a compact and high-efficiency frequency-doubling linear cavity.

A Watt-level continuous and single frequency blue laser at 461 nm is obtained by frequency-doubling an amplified diode laser operating at 922 nm via a LBO crystal in a resonant Fabry-Pérot cavity. We achieved a best optical conversion efficiency equal to 87% with more than 1 W output power in the blue, and limited by the available input power. The frequency-converted beam is characterized in terms of long term power stability, residual intensity noise, and geometrical shape. The blue beam has a linewidth of the order of 1 MHz, and we used it to magneto-optically trap 88Sr atoms on the 5s2 1S0 - 5s5p 1P1 transition. The low-finesse, linear-cavity doubling system is very robust, maintains the lock for several days, and is compatible with a tenfold increase of the power levels which could be obtained with fully-fibered amplifiers and large mode area fibers.

Compact, 2.95-GHz repetition-rate femtosecond optical parametric oscillator with tunable pulse repetition frequency

We report a compact femtosecond optical parametric oscillator (OPO) with a tunable repetition rate that is harmonically pumped using a 52.5 MHz Yb-doped fiber laser system. By reducing the OPO cavity length, the repetition rate can be adjusted successively from 1.935 to 2.95 GHz at 52.5 MHz intervals. The multiplication of the repetition rate is achieved by placing a nonlinear crystal in a compact linear cavity, and the minimum cavity length is 47.8 mm. The maximum signal power (205.2 mW) at 2.04 GHz is obtained at an input pump power of 2.35 W and a central wavelength of 1472 nm. The central wavelength of the signal pulses can be tuned from 1383 to 1596 nm. To the best of our knowledge, 2.95 GHz is the highest repetition rate achieved using a femtosecond OPO based on an ultrashort cavity with a length that is N times (N is an integer) shorter than that of the pump cavity.

Noise-Like Square Pulses in Both Normal and Anomalous Dispersion Regimes

Noise-like square pulses (NLSPs) have been experimentally investigated in both normal and anomalous dispersion regimes. A chirped fiber Bragg grating (CFBG) has been employed as a dispersion management element in the compact linear-cavity mode-locked Yb-doped fiber laser. The net cavity dispersion could be switched from large anomalous dispersion (-2.71 ps <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> ) to large normal dispersion (+5.33 ps <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> ), depending on the direction of CFBG inserting in laser cavity. Two kinds of NLSPs with different temporal profiles are achieved in the proposed laser. In anomalous dispersion regime, the square pulse duration can be tuned from 0.91 ns to 5.39 ns, and the maximum square pulse energy is 39.57 nJ. In normal dispersion regime, the top of the pulse is flatter, the square pulse duration can be tuned from 0.89 ns to 5.97 ns, and the maximum square pulse energy is slightly higher, up to 40.17 nJ. The output laser is linearly polarized.

Noise-like square pulses in a linear-cavity NPR mode-locked Yb-doped fiber laser

We have first experimentally demonstrated the generation of noise-like square pulses (NLSPs) in a linear-cavity mode-locked Yb-doped fiber laser. The mode-locking mechanism is based on nonlinear polarization rotation (NPR) in our simple and compact linear-cavity configuration, in which a fiber-pigtailed polarization beam splitter (PBS) is used as a mode-locking element. The pulse duration of square pulses can be tuned from 2.92 ns to 12.06 ns with the amplitude remaining constant, and the maximum output average power is 75.4 mW with the slope efficiency of 23.69%, under our pump-power condition.

Self-Q-switched and broad wavelength-tunable lasing in Tm3+-doped CaF2 single-crystal fiber

Self-Q-switched lasing was demonstrated for the first time around 2 μm in Thulium (Tm) doped CaF2 single-crystal fiber (SCF) using a compact linear cavity. Maximum average output power of 1.17 W was obtained under 2.38 W absorbed pump power, corresponding to the slope efficiency of up to 56.01%. Self-Q-switched laser with a 1.736 μs shortest pulse width at 48.80 kHz repetition rate was successfully realized. Besides, broad wavelength-tunable Tm:CaF2 SCF laser in 1859–2040 nm region was operated. These results show that the Tm:CaF2 SCF is a promising alternative for generating efficient micro diode-pumped pulsed lasers at 2 μm.

Linear‐cavity mode‐locked fibre laser with cylindrical vector beam generation

A cylindrical vector beam (CVB)-pulsed fibre laser with compact linear-cavity configuration has been demonstrated, using a two-mode fibre (TMF) Bragg grating (TM-FBG) for mode discrimination and a semiconductor saturable absorber mirror (SESAM) for passive mode-locking. As a result, mode-locked CVB pulses with fundamental repetition rate of 10.295 MHz have been obtained. Besides, with increased pump power harmonic, mode-locked CVB pulses have been achieved, for the first time.

A compact linear-cavity multi-wavelength Brillouin/thulium fiber laser in S/S+-band

• A compact Brillouin laser linear cavity system. • Multi-wavelength output over a 55 nm tuning range from 1460 to 1515 nm. • 28 Brillouin Stokes lines generated at maximum pump power of 250 mW. • Also covers the S + -band region with 5 Stokes lines. A compact Brillouin thulium-doped fluoride fiber (TDFF) multi-wavelength fiber lasers (MWFLs) operating in the S/S + band region is proposed and demonstrated. The system is based on a linear design and utilizes two Faraday mirrors at both ends of the cavity to enable bi-directional oscillation. An 11.5 m long TDFF with an absorption rate of 0.15 dB/m at 1400 nm is used as the gain medium. A stable output laser comb with 28 Stokes lines is obtained at the maximum pump power of 250 mW at the wavelength of 1488 nm. The multi-wavelength Brillouin fiber laser can also be tuned, covering a total tuning range of 55 nm from 1460 nm to 1515 nm. The proposed system is highly stable, and would have significant practical applications.

A passively Q-switched compact Er:Lu2O3 ceramics laser at 2.8 μm with a graphene saturable absorber

We have demonstrated a passively Q-switched Er:Lu2O3 ceramics laser using a monolayer graphene saturable absorber (SA). Stable pulsed operation with watt-level average power was achieved by a compact linear cavity without focusing on the SA. This is the first demonstration of a passively Q-switched mid-IR Er:Lu2O3 laser using a graphene SA. A maximum pulse energy of 9.4 μJ and a peak power of 33 W were achieved with a 247 ns pulse duration. To our knowledge, this is the shortest pulse duration, highest pulse energy, and highest peak power obtained with a graphene SA in the 3 μm wavelength region.

High-power dissipative soliton resonance fiber laser with compact linear-cavity configuration

An ultra-compact mode-locked Yb-doped fiber laser under the operation regime of dissipative soliton resonance (DSR) has been demonstrated, which exports sub-nanoscond pulses with a maximum output average power of 2.4 W. The linear-cavity configuration of the proposed fiber laser is formed by a highly reflective fiber Bragg grating at 1066 nm and a nonlinear optical loop mirror (NOLM) consisting of a 5/95 optical coupler. As a result, DSR pulses with maximum average power of 2.4 W and repetition rate of 10.119 MHz have been obtained, when pump power is 10 W. The compact DSR Yb-doped fiber laser with high output power have great potential applications in material processing, optical communications, and so on.

Continuous-Wave Widely Tunable MgO:PPLN Optical Parametric Oscillator With Compact Linear Cavity

An efficient continuous-wave, widely tunable, intra-cavity optical parametric oscillator (OPO) based on periodically poled MgO:LiNbO3 (MgO:PPLN) with a compact three-mirror linear cavity was demonstrated. The mode radii of fundamental and OPO cavities with plane and concave mirrors were calculated and theoretically compared. The result shows that the fundamental laser beam could be compressed, and its power density on the MgO:PPLN crystal could be improved by optimizing concave radii of cavity mirrors. Meanwhile, better mode matching between fundamental cavity and OPO cavity could be realized. A widely tunable signal spectrum from 1.43 to $1.79~\mu \text{m}$ and an idler spectrum from 2.62 to $4.16~\mu \text{m}$ were achieved as the OPO system derived by a diode laser end-pumped Nd:YVO4 crystal laser at 1064 nm. The maximum total output power up to 6.35 W (signal output power of about 4.24 W at $1.60~\mu \text{m}$ and idler output power of about 2.11 W at $3.17~\mu \text{m}$ ) and conversion efficiency of 31.6% were obtained at an incident pump power of 20.1 W.

Efficient continuous-wave and passive Q-switched mode-locked Er3+ : CaF2-SrF2 lasers in the mid-infrared region.

An Er3+-doped CaF2-SrF2 mixed crystal was grown using the temperature gradient technique, and its laser characteristics were studied. In a compact linear cavity, a continuous-wave output power of 712mW was obtained with the highest slope efficiency of 41.4%. Using a semiconductor saturable absorber mirror, a passive Q-switched mode-locked Er3+:CaF2-SrF2 laser emitting at 2729.5nm was demonstrated for the first time, to the best of our knowledge. The maximum average output power of 125mW was obtained at an absorbed pump power of 1.81W, and the repetition rate of the Q-switched envelope was 4.17kHz. The mode-locked pulses in the Q-switched pulse envelope had a repetition rate of 136.3MHz, and its duration was estimated to be approximately 1.78ns. These results indicate that the Er3+-doped CaF2-SrF2 mixed crystal is promising for the development of an ultrafast laser in the mid-infrared regime.

Compact passive Q-switching of a diode-pumped Tm,Y:CaF2 laser near 2 μm

Lasing was realized near a wavelength of 2 μm with a compact linear cavity by using a fiber-coupled 792-nm laser diode as the pump source and a Tm3+,Y3+ co-doped CaF2 crystal. By employing broadband graphene oxide (GO) as the saturable absorber (SA), a passive Q-switching Tm,Y:CaF2 laser was implemented for the first time. When the transmission of the output couple (OC) was 2%, the maximum average output power was measured to be 400 mW with a corresponding repetition rate of 20.22 kHz and a pulse width of 1.316 μs. A maximum continuous-wave (CW) output power of more than one watt was obtained with slope efficiency of 51.5%.

Dual-wavelength Bi2Se3-based passively Q-switching Nd3+-doped glass all-fiber laser

We demonstrate a dual-wavelength passively Q-switched Nd3+-doped glass fiber laser using a few-layer topological insulator Bi2Se3 as a saturable absorber (SA) for the first time, to the best of our knowledge. The laser resonator is a simple and compact linear cavity using two fiber end-facet mirrors. The SA is fabricated by Bi2Se3/polyvinyl alcohol composite film. By inserting the SA into the laser cavity, a stable Q-switching operation is achieved with the shortest pulse width and maximum pulse repetition rate of 601 ns and 205.2 kHz, respectively. The maximum average output power and maximum pulse energy obtained are about 6.6 mW and 38.8 nJ, respectively.

Investigation on the effect of output mirror transmission in WS2-based red-light passively Q-switched Pr:ZBLAN all-fiber lasers.

We report the experimental investigation of visible passively Q-switched Pr3+-doped all-fiber lasers with tungsten disulfide (WS2) saturable absorber, where red-light short-pulse generations from different output mirror transmissions are systemically characterized. The proposed simple and compact all-fiber linear cavity was constructed by a fiber-pigtail-based blue laser-diode pump, a Pr3+-doped fluorozirconate glass active fiber, and the fiber end-facet mirrors. Integrating a free-standing layered WS2 film into the laser cavity initiated the Q-switching operation. Stable microsecond-duration output pulses with kilohertz repetition rates are achieved, corresponding to a few mW/nJ average output power and single-pulse energy. The comparisons on red-light Q-switched output parameters for output transmissions of both ∼40% and ∼80% are performed. This work could provide a useful guideline to manipulate the output performance of visible pulsed all-fiber lasers for various practical applications.

High power fiber-coupled acousto-optically Q-switched 532 nm laser with a side-pumped Nd:YAG laser module

We demonstrated a high power laser at 532 nm by frequency-doubling of an acousto-optically Q-switched and side-pumped Nd:YAG laser at 1064 nm using a compact linear cavity. The average output power of the pulsed fundamental laser at 1064 nm was as high as 299 W. The laser employed two acousto-optic Q-switches placed orthogonally with each other to improve the hold-off capacity. Through intracavity frequency doubling with a type II non-critically phase-matched LBO crystal, a 165 W average power of the frequency-doubled output at 532 nm was generated with a repetition rate of 20 kHz and pulse width of 160 ns, which corresponds to a pulse energy of 8.25 mJ and a peak power of 51.6 kW, respectively. The output power of the green laser was very stable and the stability at various output powers was measured. The RMS instability was ±1.4% when the output power of 532 nm was 135 W. After coupling the 165 W output power at 532 nm into an 800 μm fiber, the final output from the optical fiber was 149 W with a coupling efficiency of 90.3%.

28 μm passively Q-switched Er:CaF_2 diode-pumped laser

A mid-infrared Er doped CaF2 crystal was successfully grown by the bridgeman method. Efficiently continuous wave and Q-switched laser operations were demonstrated at 2.8 μm with a 4 at.% Er doped CaF2 crystal end-pumped by a fiber-coupled 974 nm diode laser. The continuous wave output power of 295 mW was obtained in a compact linear cavity. A stable 2.8 μm passively Q-switched Er:CaF2 laser was also demonstrated with a graphene saturable absorber. Under an absorbed pump power of 2.353 W, an average output power of 172 mW was generated with a pulse duration of 1.324 μs and a repetition rate of 62.70 kHz, corresponding to the single pulse energy of 2.74 μJ and the peak power of 2.07 W, respectively. The high-quality Er:CaF2 crystal and the monolayer graphene are an ideal combination to directly obtain a near 3 μm mid-infrared region pulse laser.

Watt-level narrow-linewidth Nd:YAG laser operating on 4F3/2→4I15/2 transition at 1834 nm.

We report on a 808 nm diode-pumped Nd:YAG narrow linewidth laser at 1834.25 nm using a compact two-mirror linear cavity. In free-running mode, a maximum output power of 1.10 W is obtained with a slope efficiency of about 11.1% at a cooling temperature of the laser crystal of 18°C. Decreasing this temperature down to 8°C increases the output power linearly up to 1.31 W. Shortening the laser cavity reduces the output power down to about 0.70 W but on a single longitudinal mode. These laser results represent the best laser performance ever achieved with any Nd-doped bulk material in the 1.8 µm mid-infrared spectral range.

Diode-pumped simultaneous multi-wavelength linearly polarized Nd:YVO4 laser at 1062, 1064 and 1066 nm

We report on a diode-end-pumped simultaneous multiple wavelength Nd:YVO4 laser. Dual-wavelength laser is achieved at a π-polarized 1064 nm emission line and a σ-polarized 1066 nm emission line with total maximum output power of 1.38 W. Moreover, tri-wavelength laser emission at the π-polarized 1064 nm emission line and σ-polarized 1062 and 1066 nm emission lines can also be obtained with total maximum output power of about 1.23 W, for the first time to our knowledge. The operation of such simultaneous dual- and tri-wavelength lasers is only realized by employing a simple glass etalon to modulate the intracavity losses for these potential lasing wavelengths inside of an intracavity polarizer, which therefore makes a very compact two-mirror linear cavity and simultaneous orthogonal lasing possible. Such orthogonal linearly polarized multi-wavelength laser sources could be especially promising in THz wave generation and in efficient nonlinear frequency conversion to visible lasers.