High Slope Efficiency Research Articles

Highly efficient LD-pumped 607 nm high-power CW Pr3+: YLF lasers

We demonstrated a 607 nm high-power continuous-wave (CW) orange laser based on a 12-mm-long a-cut Pr3+:YLF crystal with high slope efficiency and a low doping level. A maximum output power of 4.88 W with a slope efficiency of ~49% was achieved at an absorbed pump power of 12.15 W, and no output saturation power was observed. To improve the laser beam quality, we designed a concave-plane cavity and achieved an output power of 3.80 W with M2 factors of ~1.7 and ~2.2 in the horizontal and vertical directions, respectively, by means of a novel output coupler with tunable transmission. In addition, theoretical analyses were conducted to explain our designs, and the corresponding simulated results were presented.

Ultrafast fiber laser based on HfSe2 saturable absorber

We demonstrate the HfSe2 saturable absorber (SA) for the generation of ultrafast pulse laser. The HfSe2 SA device is fabricated by integrating HfSe2 nanosheets (NSs) with a microfiber. The material and optical characteristics of HfSe2 NSs show their high quality. The nonlinear optical absorption of HfSe2 SA is measured with a modulation depth of 5.8%. Stable soliton mode-locked laser based on HfSe2 SA is realized at the central wavelength of 1561.43 nm with pulse duration of 297 fs and the maximum pulse energy of 2.68 nJ. Our soliton fiber laser has a maximum output power of 48.5 mW with a high slope efficiency of 12.8%, which indicate that HfSe2 is a good candidate of SA for high efficient ultrashort pulses generation.

Watt-level mid-infrared continuous-wave Tm:YAG laser operating on the 3H4 → 3H5 transition

We report on the first continuous-wave mid-infrared Tm:Y3Al5O12 laser operating on the 3H4 → 3H5 transition. The 3.2 at.% Tm:Y3Al5O12 laser generated a maximum output power of 1.07 W at ~2.19 & 2.32 μm with a high slope efficiency of 46.3% (vs. the absorbed pump power) exceeding the Stokes limit. Depending on the output coupling and the pump power, a set of discrete laser lines in the range of 2.164–2.346 μm was observed. The spectroscopic properties of Tm:Y3Al5O12 relevant for the mid-infrared laser operation are revised. The maximum stimulated-emission cross-section for the 3H4 → 3H5 transition is 0.35 × 10−20 cm2 at 2324 nm and the emission bandwidth is ~37 nm. The overlap of the 3F4 → 3H6 and the 3H4 → 3H5 transitions is quantified revealing the formulas for Stokes and anti-Stokes phonon sidebands of emission bands. Tm:Y3Al5O12 is promising for broadly tunable (2.1–2.5 μm) and mode-locked mid-infrared oscillators.

High-quality tuning of cholesteric liquid crystal lasers based on polymer composite system

Electrically fine tuning is demonstrated in a cholesteric liquid crystal (ChLC) laser based on the polymer composite system. Photo-polymerization in the mixture of LC monomer and LC hardly causes phase separation due to miscibility, forming a microscopically well-mixed polymer-LC composite structure like gel. Light scattering in the polymer-LC composite system decreases with increasing the polymer component, and the composite of equal parts of the polymer and LC exhibits high transparency in electric modulation of the selective reflection band, resulting in high-quality tuning of lasing wavelength in ChLC laser. In tuning operation, the ChLC laser retains a high slope efficiency greater than 19%, a low threshold smaller than 3 nJ/pulse, and a spectral linewidth narrower than 0.13 nm, while the change in lasing wavelength is fully continuous and reaches 13 nm.

Diode‐Pumped Laser Operation of Tb3+:LiLuF4 in the Green and Yellow Spectral Range

AbstractHere, a diode‐pumped laser based on trivalent terbium (Tb3+) as the active ion is reported. Optical pumping of a Tb3+‐doped lithium‐lutetium‐fluoride (LiLuF4) crystal with up to 200 mW from a diode laser emitting at a wavelength of 488.2 nm enables continuous‐wave lasing directly in the green and in the yellow. At an emission wavelength of 542 nm, the laser reaches an output power of up to 43.8 mW with a high slope efficiency of 52% with respect to the absorbed pump power. The yellow laser at 587 nm exhibits a slope efficiency of 22% and the output power of 13.8 mW is only limited by the available pump power. Laser thresholds as low as 14 and 27 mW of absorbed pump power are observed for the green and yellow, respectively. The investigations toward further optimization of the laser performance reveal that highly Tb3+‐doped materials are suitable for compact, efficient, and affordable diode‐pumped solid‐state lasers with direct emission in the visible spectral range. These results are of high relevance, as in particular for the yellow spectral range such systems are currently not available.

Q-switched tunable fiber laser utilizing silver nanoparticles deposited onto PVA film as saturable absorber

We demonstrate a broadband-tunable Q-switched fiber laser by exploiting a silver nanoparticles (SNP) saturable absorber (SA) as a Q-switcher. The SA device was prepared by depositing SNP onto a polyvinyl alcohol thin film utilizing an electron beam deposition technique. The SA was then incorporated into an erbium-doped fiber laser cavity to generate Q-switched pulses. By adjusting a tunable filter inside the laser cavity, the generated Q-switching pulses train operation could be tuned from 1535 to 1565 nm with the highest slope efficiency of 25.3% obtained at 1560 nm. At this operating wavelength, the laser repetition rate was raised from 15.1 to 28.4 kHz, whereas the pulse width shrunk from 19.45 to 11.85 μs with an increasing laser diode power from 14.9 to 37.8 mW. The pulse energy of 27.5 nJ was obtained at 37.8 mW pump power.

Modulated photonic-crystal surface-emitting laser with elliptical lattice points for two-dimensional coupling enhancement

Modulated photonic-crystal surface-emitting lasers (M-PCSELs) are new semiconductor lasers that can emit a laser beam in arbitrary directions. Therefore, they can be regarded as a next-generation light source for light detection and ranging. In this manuscript, we numerically investigate the characteristics of M-PCSELs, including one- and two-dimensional optical coupling constants and radiation constants, by using three-dimensional coupled wave theory. We also carry out lattice point designs and show that the two-dimensional optical coupling can be enhanced by more than four times over our previous M-PCSEL devices by employing elliptical lattice points. Moreover, we find that two-dimensional optical coupling can be maintained even when large lattice point position modulations are introduced for large radiation constants. These results indicate that more stable two-dimensional oscillation and a higher slope efficiency are expected in M-PCSELs with elliptical lattice points.

Highly efficient ­Tm3+ doped germanate large mode area single mode fiber laser

We report the fabrication of a low numerical aperture large mode area, high concentration thulium doped germanate glass fiber using a rod-in tube technique. The fiber core is 20 µm in diameter and operates in the single-mode regime in the 2 µm region. The Tm3+ ion concentration is 3×1020/cm3 and the background fiber attenuation is 1.1 dB/m in the near infrared. We also demonstrate a high-power, high-efficiency fiber laser emitting at 1950 nm using a short (21-cm-long) length of the fiber. A slope efficiency of 55.9% with respect to absorbed pump power and a maximum output power of ∼1.52W was achieved. This represents both the highest slope efficiency and the highest output power reported so far for Tm3+ doped germanate single mode fiber using in-band core pumping. The large core area, short device length and high efficiency make this fiber attractive for the development of high peak power pulsed fiber amplifiers and single-frequency fiber lasers operating in the 2 um region.

976 nm all-fiber Raman laser with high beam quality at multimode laser diode pumping

A 976 nm all-fiber Raman laser enabling high beam quality at direct multimode laser diode pumping with low beam quality (M2 > 30) is demonstrated. The laser is performed in a 100/140 multimode graded-index fiber with special in-fiber Bragg gratings that secure generation of the Stokes beam with relatively good quality (M2 ⩽ 2) and high slope efficiency of the pump-to-Stokes conversion (70%) at output powers of up to ~50 W.

Simulation and comparision of GaAs, AlGaAs and GaInP barriers in InGaAs quantum well lasers

InGaAs quantum wells with GaAs, AlGaAs and GaInP barriers have been simulated, respectively. The InGaAs/GaInP structure reveals a high material gain which could be nearly 1.4 times of that of InGaAs/GaAs. Threshold current of InGaAs/GaInP structure is less than half of InGaAs/AlGaAs. A high slope efficiency of 1.57 W/A from InGaAs/GaInP structure is observed with indium content as high as 0.35. InGaAs/GaInP structure will be the most appropriate candidate to fabricate a laser diode with high slope efficiency and low threshold current.

Loss tailoring of high-power broad-area diode lasers.

Broad-area diode lasers (BALs) with high power are highly desirable for a variety of applications. However, such lasers suffer from strongly deteriorated beam quality due to multimode behavior in the lateral direction. In this Letter, we present an approach to flexibly tailor the optical loss of different-order lateral modes by etching micro-holes on the laser mesa with controlled position and numbers. Through arranging the micro-holes at the peak positions of high-order lateral modes with an increasing number from the mesa center to both edges, high-order modes are suppressed due to a larger propagation loss than the fundamental mode. As a result of enhanced mode discrimination, we demonstrate that this technique provides a greatly improved beam quality and about two times higher brightness for 100μm wide BAL, while maintaining high power and slope efficiency output.

High-power single transverse and polarization mode VCSEL for silicon photonics integration.

We demonstrate a 6.5 mW single transverse and polarization mode GaAs-based oxide-confined VCSEL at 850 nm. High power is enabled by a relatively large oxide aperture and an epitaxial design for low resistance, low optical loss, and high slope efficiency VCSELs. With the oxide aperture supporting multiple polarization unrestrained transverse modes, single transverse and polarization mode operation is achieved by a transverse and polarization mode filter etched into the surface of the VCSEL. While the VCSEL is specifically designed for light source integration on a silicon photonic integrated circuit, its performance in terms of power, spectral purity, polarization, and beam properties are of great interest for a large range of applications.

Investigation of photo-darkening effect in ytterbium-doped microstructure optical fiber through the laser sintering fabrication method

Here we investigated photo-darkening (PD) effect and its influence on laser performance in Yb3+-doped microstructure optical fiber made through the laser sintering technique (LST). Through measuring the temporal evolution of PD excess loss at 633 nm and fiber lasing characteristics, it was found that the home-made fiber has relatively low PD and high slope efficiency. The obtained PD equilibrium loss αeq at 633 nm is 1.07 dB/m. After 30 h 976 nm laser irradiation, the fiber presents a quite small power degradation of 0.45 %. Moreover, the laser slope efficiency shows a small decline of 0.26 %, from 81.03 % to 80.77 %. The investigation of optical performance demonstrates that Yb3+-doped fiber fabricated by LST has uniform elements distribution, reasonable absorption, low background loss and a relatively low PD behavior, making it a potential application for effective high-power fiber lasers.

400 mW narrow linewidth single-frequency fiber ring cavity laser in 2 um waveband.

We present a single-frequency thulium-doped fiber laser (TDFL) with a narrow linewidth of 20 kHz. Stable single-longitudinal-mode (SLM) lasing operation at 1957 nm is achieved using a segment of un-pumped polarization-maintaining thulium-doped fiber (PM-TDF) as an ultra-narrow bandwidth filter. A high optical signal-to-noise ratio (OSNR) of over 60 dB is obtained and a high power of over 400 mW is achieved with a high slope-efficiency (~45.8%) thulium-doped fiber amplifier (TDFA).

Mesa‐type quantum cascade lasers fabricated by using inductively coupled plasma reactive ion etching

Mesa-type and ridge-type InGaAs/InAlAs double-channel quantum cascade lasers (QCLs) emitting 8.15 μm wavelength were fabricated by using metal–organic chemical vapour deposition and inductively coupled plasma reactive ion etching techniques. The output power, threshold current, characteristic temperature (T 0), and slope efficiency were compared. The smooth and vertical sidewall profile enabled mesa-type QCL to exhibit the higher output power, the lower threshold current, and the higher slope efficiency than the ridge-type QCL.

2.92-µm high-efficiency continuous-wave laser operation of diode-pumped Er:YAP crystal at room temperature.

Mid-infrared lasers have attracted attention for application to the fields of medicine and industry. In this study, we demonstrate continuous-wave laser operation of a diode-pumped 5 at % Er-doped YAlO3 (YAP) single-crystal lasing at 2.92 µm with near-quantum-defect slope efficiency at room temperature. A high slope efficiency of 31% is achieved with a maximum output power of 0.674 W for a cavity length of 18 mm and an output coupler transmittance of 2.5%. This efficiency is 94% of the theoretical quantum-defect efficiency. Our results indicate that Er:YAP lasers can potentially be utilized to realize high-power mid-IR lasing.

88 GHz Q-switched mode-locked waveguide lasers modulated by PtSe2 saturable absorber

We demonstrate high-repetition-rate fundamentally Q-switched mode-locked Nd:YAG waveguide laser modulated by platinum diselenide (PtSe2) saturable absorber. The laser operation platform is a femtosecond laser-written monolithic Nd:YAG waveguide, and the saturable absorber is large-area few-layer PtSe2 that possesses relatively lower saturation intensity and higher modulation depth in comparison with graphene. With the superb ultrafast nonlinear saturable absorption properties of as-synthesized PtSe2, the waveguide laser could operate at ~8.8 GHz repetition rate and ~27 ps pulse duration, while maintaining a relatively high slope efficiency of 26% and high stability with signal-to-noise ratio (SNR) up to 54 dB. Our work indicates the promising applications of laser-written Nd:YAG waveguides and atomically thin PtSe2 for on-chip integration of GHz laser sources toward higher repetition rates and shorter pulse duration.

Suppression of higher-order modes in a large-optical-cavity waveguide structure for high-power high-efficiency 976-nm diode lasers

High-power high-efficiency broad-area diode lasers are highly efficient light sources. A study on the design of large-optical-cavity 976-nm diode lasers is presented here. Efforts were made to suppress the higher-order modes and to explore new design methods for high-power high-efficiency diode lasers. The mode distribution, confinement factor, internal optical loss and far-field pattern were numerically calculated to analyze the waveguide design. To suppress the higher-order transverse modes, both gain and loss discrimination mechanisms were experimentally investigated. By adjusting the position of the active region, successful suppression of higher-order modes can be achieved. Alternatively, higher-order modes can be suppressed by increasing the cavity length, which is attributed to the discrimination of modal loss between the higher-order modes and the fundamental mode. A high-efficiency 4-mm-long broad-area single emitter with an ultralow internal optical loss of 0.27 cm–1 and an internal quantum efficiency of 93.5% was designed and fabricated. A high slope efficiency of 1.1 W/A and >66% wall-plug efficiency was obtained at 25 °C under continuous current injection. The far-field divergence angles with 95% power content were 38° and 9.7° for the fast and slow axes, respectively, at an output power of 10.0 W.

Erbium-ring-doped fiber laser for transverse vector modes output

We propose a few-mode erbium-ring-doped fiber laser with high slope efficiency towards an individual transverse vector mode output. Based on the rate equation, specific transverse vector mode output is achieved through numerical investigations of the position and the thickness of the transverse erbium-doped region. Our results show that a thinner erbium-doped region is favorable for increasing the number of available output transverse vector mode, and the position selects desired transverse vector mode to excite. Moreover, high-order vector modes up to the third-order can be excited with appropriate erbium-doped locations. The laser output using the proposed method has merit of high slope efficiency and high mode purity. The slope efficiency and the mode purity can reach 61.25% and 99.99%, respectively. Our work may find potential applications in high-power lasers and high-order transverse mode operation of fiber lasers.

Yb3+-doped large-mode-area photonic crystal fiber for fiber lasers prepared by laser sintering technology

In this paper it is demonstrated that laser sintering technology combined with fiber fabrication by the stack and draw method can be used to realize efficient fiber lasers. More precisely, a ytterbium-doped large-mode-area photonic crystal fiber with a core obtained by laser sintering technology is studied. Electron probe micro-analysis (EPMA) mapping reveals that the elements Yb, Al and Si are distributed throughout the fiber core with an excellent homogeneity. The laser performance demonstrates a high laser slope efficiency of 81.03 % for a laser emission at 1035 nm and a low power threshold of 3.04 W within only 1 m of fiber. The optical and spectroscopic properties of the fiber are studied, together with the sensitivity of the fiber to photodarkening (PD). The results make laser sintering technology interesting for the realization of fibers with large core and complex designs toward high-power fiber lasers.