Continuous-wave Laser Operation Research Articles

Efficient passively Q switched lasers with a large-energy stored Yb:LuScO3 crystal.

Ytterbium (Yb)-ions-doped sesquioxide crystal is an attractive gain medium for a tunable and pulsed laser owing to its high thermal conductivity. In particular, it has been identified that Yb:LuScO3 has the largest energy storage property compared with other sesquioxide crystals, which is favorable for passive Q switching. In this Letter, continuous wave (CW) and the first, to the best of our knowledge, passively Q switched laser operations were demonstrated with a Yb:LuScO3 crystal. For CW laser operation, it generated the maximum output power of 8.68 W, corresponding to a slope efficiency up to 78.3%. Using Cr:YAG crystals as saturable absorbers, stable passive Q switching lasers were obtained with the Yb:LuScO3 crystal. Both the CW and Q switched lasers operate on the strongest fluorescence emission peak of 1038 nm. With Cr:YAG as the saturable absorber, efficient passively Q switched lasers with a slope efficiency of 45% were obtained with the pulse width, pulse energy, and peak power of 5.9 ns, 116 µJ, and 18.5 kW, respectively.

Novel laser crystal Nd3+: Ca(Y, Gd)AlO4: A promising candidate for laser operation beyond 1.37 µm

A novel laser crystal Nd: CaGd0.1Y0.9AlO4 (Nd3+: Ca(Y, Gd)AlO4) crystal has been successfully grown by Czochralski (CZ) method. With the introduction of Gd3+ ions, this crystal has a more disorder structure than that of the Nd: CaYAlO4 (Nd: CYA). The full width at half-maximum (FWHM) of the π polarization emission spectra at around 1365 nm for the Nd3+: Ca(Y, Gd)AlO4 crystal was 53 nm, which is larger than that of Nd: CYA (35 nm) crystals, provided clear evidence for the more disorder structure. Moreover, its wide absorption spectral was maintained compared to the Nd: CYA crystal. At the same time, the effective dual-wavelength continuous-wave laser operation at 1358.4 nm and 1374 nm was realized of the as-grown crystal for the first time. These results suggest that the Nd3+: Ca(Y, Gd)AlO4 crystal is a promising disordered laser host for solid laser operation at the wavelength longer than 1370 nm in the range of 1.3–1.4 µm.

Effects of Pr3+ doping concentration on optical properties of LaF3 crystal

The crystal compositions, fluorescence lifetimes, polarized absorption and emission spectra, and laser performance were measured with different doping concentrations of Pr:LaF3 crystals. Moreover, the effects of Pr3+ doping concentration on LaF3 crystal optical properties were expounded for the first time. The study found that high doping concentration is easy to cause cross-relaxation, which in turn leads to a decrease in the lifetime of the laser upper energy level. And then affects the output efficiency of the visible laser. The laser experiment results confirm that the maximum output power of 176 mW was obtained with Pr:LaF3 crystal of 0.5 at.% doping concentration, which is higher than output power (71.3 mW) of 1 at.% doping concentration crystal. As we all know, this is the first report about continuous-wave (cw) laser operation with Pr:LaF3 crystal pumped by an blue laser diode.

Growth, spectroscopy and CW laser operation of Ho3+ doped CaY0.9Gd0.1AlO4 single crystal

Ho3+-doped CaY0.9Gd0.1AlO4 single crystal was successfully grown by the Czochralski technique for the first time. The polarized absorption spectra, polarized luminescence spectra and fluorescence decay curve of the crystal were investigated at room temperature. The spectroscopic parameters are calculated based on Judd–Ofelt theory, the values of Ω2,4,6 were calculated to be 3.16 × 10−20 cm2, 3.93 × 10−20 cm2, 0.91 × 10−20 cm2, respectively. The Ho:CaY0.9Gd0.1AlO4 crystal exhibits strong emission at 2013 nm for π- and 2032 nm for σ-polarizations with stimulated emission cross section of 6.64 × 10−20 cm2 and 1.90 × 10−20 cm2, respectively. The fluorescence lifetime of the 5I7 level was measured to be 6.60 ms. The continuous-wave (CW) laser operation of Ho:CaY0.9Gd0.1AlO4 crystal around 2 μm was demonstrated.

Spectroscopy and 2.1 µm laser operation of Czochralski-grown Tm3+:YScO3 crystals.

We report on growth, temperature-dependent spectroscopy, and laser experiments of Tm3+-doped YScO3 mixed sesquioxide crystals. For the first time, cm3-scale laser quality Tm3+:YScO3 crystals with 2.2 at.% and 3.1 at.% doping levels were grown by the Czochralski method from iridium crucibles. We reveal that the structural disorder in the mixed crystals allows for broad and smooth spectral features even at cryogenic temperatures. We obtained the first continuous wave laser operation in this material at wavelengths around 2100 nm using a laser diode emitting at 780 nm as a pump source. A maximum slope efficiency of 45% was achieved using a Tm3 + (3.1 at.%):YScO3 crystal. Our findings demonstrate the high potential of Tm3+-doped mixed sesquioxides for efficient ultrafast pulse generation in the 2.1 µm range.

250 fs, 130 mW Laser With Tunable Pulse Repetition Rate From 0.5 to 1.3 GHz

We report a compact ultrafast solid-state laser source with a pulse repetition rate continuously tunable in the range of 0.56–1.23 GHz. The optical cavity design allows a user to vary the repetition rate only by moving positions of two optical components inside the resonator, without a need to exchange components or realignment. The Yb:KYW crystal based cavity emits 250 femtosecond pulses at a central wavelength around 1040 nm, with a self-starting SESAM modelocking. In a robust modelocked operation mode, an average power up to 130 mW is achieved using a stabilized single mode pump diode at a wavelength of 981 nm, while the laser in continuous wave (CW) mode delivers up to 270 mW. Atmospheric air cooling was sufficient for both CW and modelocked laser operation. Quite low noise performance was observed, with carrier frequency SNR higher than 80 dB, although the measurements were taken with the open breadboard setup.

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.