Continuous-wave Laser Operation Research Articles

Tunable continuous-wave laser operation of Tm3+ ion doped tellurite glass near 2 μm

We provide an experimental investigation of the absorption saturation and 1.9-μm lasing characteristics of a bulk Tm3+:TZLN glass with the host composition of 74TeO2–12ZnO–4La2O3–10Na2O. By using a z-scan saturation measurement, the absorption cross section at 794 nm was determined to be 5×10−21cm2, in reasonable agreement with the value of 6×10−21cm2 obtained from small-signal transmission measurement. In lasing experiments, double pumping was employed at 794 nm and the bulk Tm3+:TZLN glass laser operated at the free running wavelength of 1926 nm. As high as 15.4 mW of continuous-wave output power was obtained with a 2.15% transmitting output coupler at the absorbed pump power of 284 mW. The slope efficiency with respect to the absorbed pump power was 7.1%. By using the threshold and power efficiency data, the stimulated emission cross section was further determined to be 6.8×10−21cm2at 1926 nm. Finally, continuous tuning of the laser output was demonstrated between 1845 and 1973 nm by using a quartz birefringent plate.

Mid-IR tunable CW and passively Q-switched laser operation of Dy-doped fluoride fiber

We report a comprehensive characterization of tunable continuous-wave (CW) and passive Q-switching laser performance of Dy-doped zirconium fluoride fiber emitting around 3 µm. The in-band pumped CW laser operation is investigated for pump wavelengths varying from 2.7 µm to 2.825 µm, for fiber lengths ranging from 0.4 m to 2 m, and for output coupling efficiency from 10% to 50%, leading to a maximum laser slope efficiency of 44% and a tuning range larger than 300 nm. With Findlay-Clay analysis and Rigrod analyses, optimal cavity parameters are retrieved, paving the way for further optimizations in performance. The passively Q-switched laser operation of Dy-doped fluoride fiber is achieved employing a semiconductor saturable absorber mirror for the first time, demonstrating a stable operation with a minimum pulse duration of 580 ns, a highest repetition frequency of 103 kHz and a pulse energy up to 300 nJ.

Continuous-Wave Operation of Microcavity Quantum Cascade Lasers in Whispering-Gallery Mode

Continuous-Wave Operation of Microcavity Quantum Cascade Lasers in Whispering-Gallery Mode

Laser-diode-pumped Tm:SrF2 single crystal for high efficiency CW laser operation at ∼2 µm.

A Tm:SrF2 single crystal is grown by a modified temperature gradient technique (TGT). A study of the fluorescence characteristics and laser performance is carried out. Under laser-diode (LD) end-pumping, a continuous-wave (CW) laser is demonstrated. A slope efficiency of up to 81.8% is first achieved in the Tm-doped single crystals, which is extremely close to the photon quantum efficiency of 2.00. Such a high photon quantum efficiency is caused by the effective cross-relaxation process between Tm3+ ions. A maximum output power of 4.082 W is also obtained. The laser performance indicates that Tm:SrF2 is a promising candidate for highly efficient ∼2 µm lasers.

Polarized spectroscopy and diode-pumped laser operation of disordered Yb:Ca3Gd2(BO3)4 crystal

We report on the growth, structure, polarized spectroscopy and efficient continuous-wave laser operation of an Yb3+-doped disordered calcium gadolinium borate crystal, Yb3+:Ca3Gd2(BO3)4 (Yb:GdCB). Yb:GdCB belongs to the orthorhombic class [sp. gr. Pnma, lattice parameters a = 7.1937(0) Å, b = 15.5311(3) Å, c = 8.6140(7) Å]. The structure disorder of this material originates from a random distribution of Ca2+ and Gd3+|Yb3+ cations over three non-equivalent lattice sites. This leads to broad and smooth (“glassy-like”) absorption and emission spectra at room and low temperatures. The stimulated-emission cross-section of Yb3+, σSE is 0.42×10−20 cm2 at 1025.1 nm for light polarization E || c and the luminescence lifetime of the 2F5/2 state is 644 µs. Continuous-wave laser performance of the Yb:GdCB crystal was evaluated under high-power diode-pumping at 976 nm for three crystal orientations along the crystallographic axes. For an a -cut crystal, a maximum output power of 5.58 W was achieved at ∼1057 nm with a slope efficiency of 51.7% and a linear laser polarization ( E || c ). The demonstrated power scaling capabilities and broadband emission properties of Yb:GdCB indicate that it is promising for generation of sub-50 fs pulses from passively mode-locked lasers at ∼1 µm.

Ultra-low threshold lasing through phase front engineering via a metallic circular aperture

Semiconductor lasers with extremely low threshold power require a combination of small volume active region with high-quality-factor cavities. For ridge lasers with highly reflective coatings, an ultra-low threshold demands significantly suppressing the diffraction loss at the facets of the laser. Here, we demonstrate that introducing a subwavelength aperture in the metallic highly reflective coating of a laser can correct the phase front, thereby counter-intuitively enhancing both its modal reflectivity and transmissivity at the same time. Theoretical and experimental results manifest a decreasing in the mirror loss by over 40% and an increasing in the transmissivity by 104. Implementing this method on a small-cavity quantum cascade laser, room-temperature continuous-wave lasing operation at 4.5 μm wavelength with an electrical consumption power of only 143 mW is achieved. Our work suggests possibilities for future portable applications and can be implemented in a broad range of optoelectronic systems.

Spectroscopy and continuous wave laser operation of Tm3+-doped YScO3 mixed sesquioxide crystal

Spectroscopy and continuous wave laser operation of Tm³⁺-doped YScO₃ mixed sesquioxide crystal

Growth, spectral properties, and laser demonstration of Yb3+ doped K5Bi(WO4)0.22(MoO4)3.78 crystal

A novel 15at. % Yb3+ ion doped K5Bi(WO4)0.22(MoO4)3.78(Yb: KBWM) crystal with a disordered structure is successfully grown by Czochralski (CZ) method. The crystal growth, structure, optical properties, and laser performance were investigated. With the introduction of the (WO4)2- anionic group, not only maintains the crystal structure of K5Bi(MoO4)4, but also results in a non-uniform broadening of the spectra. The absorption cross-section is 2.5 × 10−20 cm2 at 975 nm. The stimulated emission cross-section is 1.2 × 10−20 cm2 at 1014 nm, with a full width at half maximum (FWHM) of 47.2 nm. The fluorescence lifetime is 730.6 μs. Furthermore, continuous wave laser operations are achieved in Yb: KBWM crystal with different output coupler transmissions. Slope efficiency as high as 11.8% with respect to the pump power and an output power of 59.6 mW were achieved with a laser diode-pumped Yb: KBWM laser. The results show that the anion group modified crystal Yb: KBWM may be used in solid-state tunable and ultra-fast lasers.

LD-pumped high-power continuous-wave Pr3+:YLF deep red lasers at 718.5 and 720.8 nm

We demonstrated 22 W LD-pumped high-power continuous-wave (CW) deep red laser operations at 718.5 and 720.8 nm based on an a-cut Pr3+:YLF crystal. The output power of both polarized directions reached the watt-level without output power saturation. A single wavelength laser operated at 720.8 nm in the π-polarized direction was achieved, with a high output power of 4.5 W and high slope efficiency of approximately 41.5%. To the best of our knowledge, under LD-pumped conditions, the laser output power and slope efficiency are the highest at 721 nm. By using a compact optical glass plate as an intracavity etalon, we suppressed the π-polarized 720.8 nm laser emission. And σ-polarized single-wavelength laser emission at 718.5 nm was achieved, with a maximum output power of 1.45 W and a slope efficiency of approximately 17.8%. This is the first time that we have achieved the σ-polarized laser emission at 718.5 nm generated by Pr3+:YLF lasers.

SESAM mode-locked Yb:SrLaAlO4 laser

We report on a detailed investigation of continuous-wave and SESAM mode-locked (ML) laser operation of an Yb:SrLaAlO4 laser. Pumped with a high-brightness fiber laser at 976 nm, the ML Yb:SrLaAlO4 laser delivered soliton pulses as short as 38 fs at 1071 nm with an average output power of 86 mW and a pulse repetition rate of ∼59 MHz. The maximum average output power reached 1.05 W at 1054 nm for longer pulses (94 fs), corresponding to a peak power of 146 kW and an optical efficiency of 38.6%. To the best of our knowledge, this is the first demonstration of SESAM ML operation of the Yb:SrLaAlO4 laser.

Structural disordered orthophosphate crystal Nd3+:YBa3(PO4)3 with cubic symmetry

A novel laser crystal Nd3+-doped yttrium barium phosphate (Nd:YBa3(PO4)3, hereafter Nd:YBP) with disordered crystal structure was reported. Single crystal growth, thermal, spectral and laser performances were investigated. The thermal conductivity at room temperature was found to be 1.35 W·m−1·K−1 and shown an increased tendency with increased temperature. The spontaneous transition probabilities, radiation lifetime and other parameters were evaluated by using the Judd-Ofelt (J-O) theory. The maximum absorption and emission cross sections for Nd:YBP crystal were obtained to be ∼ 2.32 × 10−20 cm2 (@ 804 nm) and 6.72 × 10−20 cm2 (@ 1056 nm), respectively. The measured fluorescence lifetime for Nd:YBP crystal was equal to 351 μs. Furthermore, diode-pumped continuous-wave laser operation was firstly realized near 1060 nm. The slope efficiency was found to be approximately 22% and the maximum output power for Nd:YBP crystal was 256 mW. Results reveal that the disordered crystal Nd:YBP might be further optimized for uses in laser field.

Tunable continuous-wave dual-wavelength laser operation of Pr3+:LiYF4 around 900 nm

We present here the first tunable continuous-wave (CW) simultaneous dual-wavelength laser operation of a Pr3+:LiYF4 crystal in the 900 nm spectral range using a single birefringent filter (BF) under excitation with a frequency doubled optically pumped semiconductor laser. By adjusting the rotation angle of the BF, the CW simultaneous dual-wavelength lasers operating at 869 and 915 nm, 894 and 915 nm, 915 and 923 nm, were obtained respectively.

Spectral properties and laser operation of Nd3+-doped mixed sesquioxide LuYO3 ceramic

The absorption spectrum, fluorescence spectrum and fluorescence time of a mixed sesquioxide Nd:LuYO3 ceramic were measured at room temperature. Judd-Ofelt theory was applied to calculate the spectral parameters of Nd:LuYO3. The absorption cross section at 812 nm was calculated to be 0.99 × 10−20 cm2 with full width at half maximum (FWHM) of 47.69 nm. The emission cross-section at 1077 nm was calculated to be 5.24 × 10−20 cm2 with FWHM of 11.62 nm. The fluorescence lifetime and quantum efficiency of the 4F3/2 multiplet were determined to be 228.4 μs and 85.2%, respectively. Continuous-wave (CW) laser operation of Nd:LuYO3 ceramic was demonstrated. Simultaneous laser operation at 1075.24 and 1080.03 nm was achieved with maximum output power of 490 mW and slope efficiency of 6.36%.

Thermal effect of InP/InAs nanowire lasers integrated on different optical platforms

III-V nanowire lasers for future photonic on-chip processors require continuous-wave operation at room temperature; however, this has not been achieved yet due to heating effects. In this work, the heating effects limiting laser performance is systematically investigated for nanowires placed on Au-coated substrates before and after Al2O3 deposition and on Si and SiN waveguides. Our findings indicate that nanowire heating is strongly related to the thermal resistance between the nanowires and substrates. Our results reveal the potential for continuous-wave nanowire laser operation, towards future photonic on-chip processors with nanowires integrated on photonic platforms.

Nd-doped structurally disordered YSr3(PO4)3 single crystal: Growth and laser performances

Disordered-structure crystals have drawn increasing attention as promising ultrashort laser material hosts owing to their broad linewidth. Herein, a novel disordered Nd:YSr3(PO4)3 (Nd:YSP) crystal with good quality was successfully grown via the Czochralski pulling technique. The absorption and fluorescence spectra of the Nd:YSP single crystal were recorded at ambient temperature. The maximum absorption cross section for Nd:YSP single crystal is found to be approximately 3.89 × 10−20 cm2. The stimulated emission cross section for Nd:YSP crystal at ∼1060 nm was determined to be 7.64 × 10−20 cm2 with the full width half maximum value of 22 nm. The fluorescence lifetime of the Nd3+ ions in the Nd:YSP crystal is fitted to be 288 μs. Diode-pumped continuous-wave laser operation is firstly realized at approximately 1060 nm. The maximum output power value from the Nd:YSP crystal is 714 mW, corresponding to a slope efficiency of ∼12.8%. The results indicate that the Nd:YSP crystal with a disordered structure may be a promising disordered laser host.

Multimode oscillation Q-switched mode-locking fiber laser based on gain equalized few-mode Er-doped fiber

We propose and demonstrate experimentally multimode Q-switched mode-locking (QML) fiber laser signal generation based on a long few-mode Er-doped fiber (FM-EDF). The erbium-doped profile of the fiber has been optimized to equalize the modal gain. The fiber supporting six modes has a total length of 5.5 m, a part of the fiber is used as a gain medium, and the unpumped part of the fiber is used as a saturable absorber. Multimode oscillation lasers in the state of the continuous wave laser operation, Q-switching, and QML state pulse laser operation were observed and measured at different pump powers by adjusting the polarization controller. A 1570-nm multimode QML pulse train was obtained, when the pump power was about 2.4 W. The width of the Q-switched envelope was 19 μs, and the repetition rate was 17.4 kHz. The stable mode-locked pulses repetition rate in Q-switched envelopes was 13.18 MHz. These temporal pulses can also be observed under the case of partly blocking the beam profile, and the part of the spectral signal gradually disappeared. The mode number in the laser was checked by a homemade mode selection photonic lantern. The results showed that the fiber laser had multimode oscillation, and the modes in generated signal were ≥5. The multiple transverse modes of the generated lasers are all in QML state at the same time. To the best of our knowledge, this is the first experimental demonstration of a multimode QML fiber laser using a long FM-EDF.

Spectroscopy and 2.8 μm laser operation of Er3+-doped (Lu, Y, Sc)-mixed garnet crystal

We report on the spectropic and continuous-wave (CW) laser properties of a novel Er 3+ -doped mixed garnet (Er:LuYSGG) crystal. The maximum phonon energy of Er:LuYSGG was measured to be 720 cm −1 , which is lower than that of Er:YSGG crystal. Fluorescence lifetimes of 4 I 11/2 and 4 I 13/2 levels amounts to 2.1 ms and 3.2 ms, indicating a potential capability for mid-infrared laser emission. For the CW laser operation, a maximum output power of 472 mW was achieved at 2797 nm, with a slope efficiency of as high as 24%. • An Er 3+ -doped (Lu, Y, Sc)-mixed garnet crystal that has a long fluorescence lifetime ( 4 I 11/2 : >2 ms) is proposed. • The phonon energy of Er:LuYSGG crystal is further reduced compared with that of Er:YSGG. • CW laser performance of Er:LuYSGG crystal gives a slope efficiency of 24%, confriming the feasibility of further power improvement.

Polarized spectral properties and laser operation of Nd:SrAl12O19 crystal

Nd:SrAl11O19 (Nd:SRA) crystal has been grown by the Czochralski method. Polarized absorption spectra, polarized fluorescence spectra and fluorescence lifetime were investigated. For σ-polarization, the peak absorption cross section at 798 nm is 2.08 × 10−20 cm2 with full width at half maximum (FWHM) of 10.2 nm and the peak emission cross section is 3.36 × 10−20 cm2 at 1048.5 nm with FWHM of 4.80 nm. The Judd-Ofelt parameters Ω2,4,6 were obtained to be 0.51 × 10−20 cm2, 2.08 × 10−20 cm2, and 2.12 × 10−20 cm2, respectively. Continuous-wave laser operation of the a-cut and c-cut Nd:SRA sample has been demonstrated. The maximum output power of 8.33 W was achieved from c-cut sample at an absorbed power of 27.73 W, corresponding to a slope efficiency of 31.3%.

Ultralow-Threshold Continuous-Wave Room-Temperature Crystal-Fiber/Nanoperovskite Hybrid Lasers for All-Optical Photonic Integration.

Continuous-wave (CW) room-temperature (RT) laser operation with low energy consumption is an ultimate goal for electrically driven lasers. A monolithically integrated perovskite laser in a chip-level fiber scheme is ideal. However, because of the well-recognized air and thermal instabilities of perovskites, laser action in a perovskite has mostly been limited to either pulsed or cryogenic-temperature operations. Most CW laser operations at RT have had poor durability. Here, crystal fibers that have robust and high-heat-load nature are shown to be the key to enabling the first demonstration of ultralow-threshold CW RT laser action in a compact, monolithic, and inexpensive crystal fiber/nanoperovskite hybrid architecture that is directly pumped with a 405 nm diode laser. Purcell-enhanced light-matter coupling between the atomically smooth fiber microcavity and the perovskite nanocrystallites gain medium enables a high Q (≈1500) and a high β (0.31). This 762 nm laser outperforms previously reported structures with a record-low threshold of 132nW and an optical-to-optical slope conversion efficiency of 2.93%, and it delivers a stable output for CW and RT operation. These results represent a significant advancement toward monolithic all-optical integration.

Увеличение оптической мощности микродисковых лазеров InGaAs/GaAs, перенесенных на кремниевую подложку методом термокомпрессии

The output power is studied under continuous-wave operation of microdisk lasers with InGaAs/GaAs quantum well-dots hybridly integrated with a silicon substrate with the epitaxial side down using the thermocompression bonding method. Owing a decrease in the thermal resistance and suppression of self-heating, an increase in the values of currents is observed at which the power is saturated and the lasing is quenched, as well as an increase in the peak power. In microdisks with a diameter of 19 µm, the highest output optical power in the continuous wave regime was 9.4 mW.