Continuous-wave Laser Operation Research Articles

Tm3+-doped LuYO3 mixed sesquioxide ceramic laser: effective 2.05 μm source operating in continuous-wave and passive Q-switching regimes.

Tm:LuYO3 ceramic is reported as an effective laser gain medium, for the first time to the best of our knowledge. For continuous-wave laser operation, a maximum output power of 1.55W with a slope efficiency of 19.9% is achieved at 2050nm. Passive Q-switching of the Tm:LuYO3 ceramic is operated using a Cr:ZnSe saturable absorber. Single-wavelength Q-switching at 2047nm is obtained with a maximum average output power of 0.54W, a pulse width of 120.3ns, a pulse energy of 20.5μJ, and a pulse peak power of 170.6W. Simultaneous dual-wavelength Q-switching at 1957 and 2047nm is also attained with corresponding parameter values of 0.92W, 151.6ns, 30.2μJ, and 199.1W. These results indicate that Tm:LuYO3 ceramic lasers could be a promising laser source operating in the eye-safe spectral region.

Single-mode interband cascade laser multiemitter structure for two-wavelength absorption spectroscopy

An interband cascade laser multiemitter with single-mode distributed feedback (DFB) emission at two wavelengths is presented. Continuous-wave laser operation is measured from 0°C to 40°C with threshold currents of around 25 mA and output powers of around 9 mW at 20°C. The ridge waveguide DFB structures are monolithically integrated with a spacing of 70 μm and each is provided with an individual metal DFB grating to select specific single-mode wavelengths of interest for absorption spectroscopy. The emission windows at 3.92 and 4.01 μm are targeting hydrogen sulfide and sulfur dioxide, which are of importance for industrial applications since both gases are reagents of the Claus process in sulfur recovery units, recovering elemental sulfur from gaseous hydrogen sulfide.

Scheme for achieving a continuous-wave laser operation at 1178 nm.

We report for the first time, to the best of our knowledge, a new scheme for generating the important 1178nm laser. Based on a high-power 1018nm fiber laser as the pump source and chemical vapor deposition diamond as the Raman gain medium, the Raman laser was capable of generating 34.6W output power centered at 1178.02nm. As far as we know, 34.6W is the highest output power of a 1178nm laser obtained within a crystalline Raman gain medium. The experimental results show the superiority of our scheme in obtaining 1178nm laser generation.

Bulk crystal growth and thermal, spectroscopic and laser properties of disordered Melilite Nd:Ca2Ga2SiO7 single crystal

A large sized Nd-doped Ca2Ga2SiO7 single crystal was successfully grown by the Czochralski technique. The effective segregation coefficient of Nd3+ was measured to be 1.16. The thermal, spectroscopic and laser properties were systematically investigated. The thermal conductivity was found to increase with increasing temperature, exhibiting glass or alloy like behavior, and is inherently associated with the disordered structure of the Ca2Ga2SiO7 crystal. The polarized absorption and fluorescence spectra were measured at room temperature, and the spectrum parameters were calculated using the Judd-Ofelt theory. Furthermore, continuous wave laser operation at 1.06 μm along the crystallographic a- and c-axes was demonstrated. A laser output power of 430 mW with an optical conversion efficiency of 14.2% and a slope efficiency of 16.7% was achieved. These results show that Nd:Ca2Ga2SiO7 holds excellent promise for use as a disordered crystalline laser material.

Growth by the μ-PD Method and Visible Laser Operation of a Single-Crystal Fiber of Pr3+:KY3F10

We report on the first growth, spectroscopy, and visible laser operation of a single-crystal fiber (SCF) of KY3F10 (KYF) grown by the micro-pulling-down (μ-PD) method, doped with Pr3+ ions. This material has a cubic lattice, which makes it appealing for use in the industry. However, KYF crystals are considered difficult to grow with high optical quality, even with well-established methods. Nevertheless, we grew a 50-mm-long SCF of Pr:KYF, which was transparent in its inner part. We studied the spectroscopic features of it in comparison with existing literature and with samples of the same crystal grown by the Czochralski method, and we did not notice any large differences. These characterizations confirmed that is indeed possible to grow high-quality crystals of Pr:KYF by the μ-PD method. Unfortunately, the crystal proved to be more brittle than typical KYF and especially difficult to polish, leading to rough and irregular facets, as evidenced by transmission measurements. Despite these issues, we obtained continuous-wave laser operation in the orange, red, and deep red regions, using a sample carved from the SCF as active medium and an InGaN-based laser diode as pump source, though with lower performances than in existing reports on this crystal.

Growth, structural, spectral and high-power continuous-wave laser operation of Yb0.11Gd0.89COB crystal

A Yb0.11Gd0.89Ca4O(BO3)3 crystal with new composition was grown by the Czochralski method. The crystal structure was measured and analyzed. The unit-cell parameters of the Yb0.11Gd0.89COB were calculated to be a=0.8089(7) nm, b=1.5987(6) nm, c=0.3545(8) nm, β=101.22°. The absorption and fluorescence spectra were measured. The maximum absorption cross-section of Yb0.11Gd0.89COB crystal was 0.79×10−20 cm2, which occurred at 976 nm with Y polarization. The emission cross-section at 1027 nm was calculated to be 0.33×10−20 cm2. The radiative lifetime τrad was calculated to be 2.74 ms. The Stark energy-level diagram of Yb3+ in the Yb0.11Gd0.89COB crystal field at room temperature was determined. The ground-state energy level 2F7/2 splitting was calculated to be as large as 1004 cm−1 and the zero-line energy was 10246 cm−1. A maximum output power of 9.35 W was achieved in continuous-wave (CW) mode, with the slope efficiency being 42.1%. Chemical etching experiment revealed that the dominating imperfections in the studied Yb0.11Gd0.89COB crystal were dislocations and sub-grain boundaries. The existence of crystal defects could cause light scattering, and degrade laser output efficiency. The influence of crystal defects on laser properties was discussed.

A diode-pumped Tm:CaYAlO4 laser at 1851 nm

Laser emission at ~1850 nm is of great interest for neural stimulation applications. In this letter, we report on the diode-pumped continuous-wave (CW) and Q-switched (QS) laser operation of Tm:CaYAlO4 at 1851 nm, for the first time to our knowledge. In the CW regime, a maximum output power up to 0.62 W is obtained with a laser slope efficiency of about 18.0%. Using a Cr:ZnSe saturable absorber, QS laser operation is achieved with a maximum average output power of 0.25 W, the narrowest pulse width of 107 ns and the highest repetition rate of 5.85 kHz. The corresponding pulse peak power and pulse energy are about 388 W and 42.8 µJ, respectively. In this Q-switched mode, wavelength tuning is also realized over about 3 nm by slightly tilting the saturable absorber.

Diode-pumped continuous-wave and passively Q-switched Nd:LuAG crystal lasers at 1.1 μm

We report on diode-pumped Nd:LuAG crystal lasers on 4F3/2→4I11/2 transition around 1.1μm in continuous-wave and passive Q-switching regimes. For continuous-wave laser operation, a dual-wavelength laser at 1117 and 1122nm is achieved with maximum output power of 5.82W and slope efficiency of about 42.8%, which is believed to be the highest output power of Nd:LuAG lasers at 1.1μm. Using an etalon to tune the lasing wavelength, a single-wavelength laser at 1114nm is also realized, for the first time to our knowledge, with maximum output power of 4.11W. Further wavelength tuning from 1113.9 to 1122.6nm is also obtainable. Passively Q-switched laser operation at 1122nm is finally performed with a maximum average output power of 0.73W, the narrowest pulse width of 21.2ns and a maximum pulse repetition rate of 14.12kHz, which leads to a maximum pulse peak power of 2.43kW and a maximum pulse energy of about 51.7μJ.

Passively Q-Switched Tm:CaGdAlO_4 laser using a Cr^2+:ZnSe saturable absorber

Diode-pumped Tm:CGA lasers at 1938 and 1854 nm are reported in continuous-wave and Q-switched regimes. For continuous-wave laser operation, the maximum output powers for the two lasers are 3.05 and 2.41 W with slope efficiencies of 33.7% and 28.5%, respectively. For Q-switching, using a Cr:ZnSe saturable absorber, the maximum average output powers reach 0.64 and 0.37 W with corresponding shortest pulse widths, maximum pulse repetition rates, maximum pulse energies and maximum pulse peak powers of (44ns, 13.9 kHz, 46 μJ, 1.04 kW) and (47 ns, 9.9 kHz, 37.4 μJ, 0.79 kW), respectively.

Toward continuous-wave operation of organic semiconductor lasers.

The demonstration of continuous-wave lasing from organic semiconductor films is highly desirable for practical applications in the areas of spectroscopy, data communication, and sensing, but it still remains a challenging objective. We report low-threshold surface-emitting organic distributed feedback lasers operating in the quasi-continuous-wave regime at 80 MHz as well as under long-pulse photoexcitation of 30 ms. This outstanding performance was achieved using an organic semiconductor thin film with high optical gain, high photoluminescence quantum yield, and no triplet absorption losses at the lasing wavelength combined with a mixed-order distributed feedback grating to achieve a low lasing threshold. A simple encapsulation technique greatly reduced the laser-induced thermal degradation and suppressed the ablation of the gain medium otherwise taking place under intense continuous-wave photoexcitation. Overall, this study provides evidence that the development of a continuous-wave organic semiconductor laser technology is possible via the engineering of the gain medium and the device architecture.

Diode-pumped passively mode-locked sub-picosecond Yb:LuAG ceramic laser**Project supported by the National Major Scientific Instruments Development Project of China (Grant No. 2012YQ120047), the National Key R&D Program of China (Grant No. 2016YFB0402105), the National Natural Science Foundation of China (Grant Nos. 61205130 and 61575212), and the Key Research Project of the Frontier Science of the Chinese Academy of Sciences (Grant No.

In this paper the laser activities of a diode-pumped Yb:LuAG ceramic which was prepared by the solid-state reactive sintering method were reported. The maximum output power was 1.86 W in the continuous wave (CW) laser operation, corresponding to a slope efficiency of 53.6%. The CW laser could be tuned from 1030 to 1096 nm by inserting a prism in the cavity. With the assist of a semiconductor saturable absorber mirror (SESAM), passive mode-locking was realized, delivering sub-picosecond pulses with 933 fs duration and an average power of 532 mW at a repetition rate of 90.35 MHz.

Nonlinear mirror mode-locked Pr:YAlO3 laser

Mode-locking of a praseodymium based solid-state laser by a nonlinear mirror is reported, for the first time to the best of our knowledge. Pr:YAlO3 crystal having 0.6 at.% of Pr3+ ions was used as an active medium. For mode-locking, a nonlinear BBO crystal together with a properly designed dichroic mirror were employed to form an output coupler with intensity dependent reflection. A continuous-wave mode-locked laser operation with a mean output power of 100 mW was achieved under 3.5 W InGaN laser diode pumping. The laser emitted 250 ps pulses with a repetition rate of 105 MHz at a center oscillation wavelength of 747 nm.

Continuous-wave laser operation of a dipole antenna terahertz microresonator

Resonators and the way they couple to external radiation rely on very different concepts if one considers devices belonging to the photonic and electronic worlds. The terahertz frequency range, however, provides intriguing possibilities for the development of hybrid technologies that merge ideas from both fields in novel functional designs. In this paper, we show that high-quality, subwavelength, whispering-gallery lasers can be combined to form a linear dipole antenna, which creates a very efficient, low-threshold laser emission in a collimated beam pattern. For this purpose, we employ a terahertz quantum-cascade active region patterned into two 19-μm-radius microdisks coupled by a suspended metallic bridge, which simultaneously acts as an inductive antenna and produces the dipole symmetry of the lasing mode. Continuous-wave vertical emission is demonstrated at approximately 3.5 THz in a very regular, low-divergence (±10°) beam, with a high slope efficiency of at least 160 mW A−1 and a mere 6 mA of threshold current, which is ensured by the ultra-small resonator size (VRES/λ3≈10−2). The extremely low power consumption and the superior beam brightness make this concept very promising for the development of miniaturized and portable THz sources to be used in the field for imaging and sensing applications as well as for exploring novel optomechanical intracavity effects.

Passively Q-Switched Tm:CaYAlO4 Laser Using a MoS2 Saturable Absorber

We report here for the first time on the diode-pumped continuous-wave laser operation of an a-cut Tm:CaYAlO4 (CYAO) crystal in a two-mirror laser configuration at about 1850 nm, which is the shortest laser wavelength ever achieved with this material, with a maximum output power of 0.88 W. Using a MoS2 saturable absorber deposited directly onto the surface of the output coupler, the Tm:CYAO laser is then operated in the Q-switched mode with a maximum output power of 0.49 W and the narrowest pulse width of $0.48~\mu \text{s}$ .

Polycrystalline Ho: LuAG laser ceramics: Fabrication, microstructure, and optical characterization

AbstractHo:Lu3Al5O12(LuAG) transparent ceramics are potential 2 μm eye‐safe laser materials. Polycrystalline 0.8 at.% Ho:LuAG ceramics with high optical quality were successfully fabricated by solid‐state reactive sintering of high‐purity oxide powders. The microstructure, the optical transmission, the spectrum characteristic, and the laser performance were investigated in this paper. The average grain size of Ho:LuAG ceramics vacuum sintered at 1830°C for 30 hour is about 14 μm. The in‐line transmittance of the sample is measured to be 81.7% and 82.0% at 1000 and 2250 nm, respectively. The absorption and the emission cross sections are calculated to be 0.88 × 10−20 cm2 at 1906 nm and 1.26 × 10−20 cm2 at 2094 nm. Using a thulium‐doped yttrium‐lithium‐fluoride (Tm:YLF) laser with the central wavelength of 1907.5 nm as the pump source, 2.67 W continuous wave (CW) laser operation at 2100.74 nm was obtained with a slope efficiency of 26.5%. The beam quality factor M2 was calculated to be 1.1, which indicated nearly diffraction‐limited beam propagation and the laser was the fundamental TEM00 Gaussian mode.

Performance and wavelength tuning of green emitting terbium lasers.

Wavelength tuning experiments in the green spectral range applying Tb3+-doped LiLuF4 and Tb3+/Na+-codoped CaF2 single crystals are presented. While in the former case almost 100 mW could be obtained throughout a total range of 7 nm, the inhomogeneously broadened emission features of Tb3+ in the CaF2-matrix allowed for a continuous tuning range exceeding 10 nm. For initial characterization, free running continuous wave laser experiments using Tb3+-doped LiLuF4, Na+:CaF2, and stoichiometric TbF3 crystals were carried out resulting in efficient continuous wave laser operation in the green spectral region. The density of active centers in TbF3 is among the highest that can be obtained in solid state gain materials. Nevertheless, a slope efficiency as high as 32% was obtained from this crystal. High Tb3+-densities are essential to compensate for the adherent low absorption cross sections at useful pump-wavelengths.

Continuous-wave laser operation of diode-pumped Tm-doped Gd3Ga5O12 crystal

We report on a diode-pumped Tm:Gd3Ga5O12 (GGG) laser at 2004 nm operated in continuous-wave mode with two-mirror linear cavity configuration. The maximum output power reaches 0.58 W with laser threshold absorbed pump power of about 0.39 W and overall slope efficiency of about 18.4%, which is believed to be the highest output power for Tm:GGG laser up to now. The Tm:GGG laser shows obvious thermally induced saturation of the output power, which indicated that power and efficiency scaling could be furtherly realized by more efficient thermal removal of the laser crystal.

Thermal radiation induced ignition of multipoint turbulent explosions

Abstract The severity of vapour cloud explosions is typically correlated with the peak over-pressure or, more accurately, with the total impulse caused by the pressure waves. The flame speed arising from strong (e.g. quasi-stable) turbulent deflagrations is frequently used to provide an indication of potential damage. However, conventional flame propagation mechanisms can present difficulties in terms of explaining the resulting damage. For example, the over-pressure in the Buncefield vapour cloud explosion was much higher than that predicted by conventional models. Alternative propagation mechanisms include intermittent localised strong explosions or detonations potentially supported by forward thermal radiation causing multi-point ignition of dust particles ahead of the advancing flame front. Such mechanisms are here explored using particles coated with acetylene black as the radiation target due to their relationship with soot emissions. A continuous wave laser operating in the near infrared was used as the radiation source with experiments performed in a flame tube using fuel lean CH4/H2/Air mixtures. It is shown that ignition kernels caused by irradiated particles can successfully be entrained into the main flow and/or recirculation zones formed around obstacles and cause multipoint explosions. The resulting relationship between fuel consumption ahead of the advancing flame and the evolution of the strength of the explosion is shown to be complex and typically lead to increased explosion durations with reduced peak pressures. It is also shown that chaotic pressure wave interactions can substantially increase both the explosion duration and the peak pressure depending on the timing of the radiation induced ignition.

High-power Yb:GGG thin-disk laser oscillator: first demonstration and power-scaling prospects.

We present the first demonstration of a thin-disk laser based on the gain material Yb:GGG. This material has many desirable properties for the thin-disk geometry: a high thermal conductivity, which is nearly independent of the doping concentration, a low quantum defect, low-temperature growth, and a broadband absorption spectrum, making it a promising contender to the well-established Yb:YAG for high-power applications. In continuous wave laser operation, we demonstrate output powers above 50 W, which is an order of magnitude higher than previously achieved with this material in the bulk geometry. We compare this performance with an Yb:YAG disk under identical pumping conditions and find comparable output characteristics (with typical optical-to-optical slope efficiencies >66%). Additionally, with the help of finite-element-method simulations, we show the advantageous heat-removal capabilities of Yb:GGG compared to Yb:YAG, resulting in >50% lower thermal lensing for thin Yb:GGG disks compared to Yb:YAG disks. The equivalent optical performance of the two crystals in combination with the easy growth and the significant thermal benefits of Yb:GGG show the large potential of future high-power thin-disk amplifiers and lasers based on this material, both for industrial and scientific applications.

Cryogenic Yb:YGAG ceramic laser pumped at 940 nm and zero-phonon-line: a comparative study

We present a comparative study on a continuous-wave laser operation of Yb-doped Y3Ga2A13O12 (Yb:YGAG) ceramic at cryogenic temperatures with conventional pumping (940 nm) and zero phonon line pumping (969 nm) under identical experimental conditions. In CW laser operation, at 80 K with ZPL pumping, a maximum output power of 6.53 W with a slope efficiency of 52.0% is achieved with respect to incident power. When compared between two pump sources at cryogenic temperatures, ZPL pumping performs better due to the difference of quantum defect between the two pump sources that results in different heat load in the sample. In passive Q-switching experiment, at 100 K, with 85% initial transmission of Cr:YAG, an average output power of 3.37 W with a repetition rate of 17.6 kHz was achieved. The pulse energy, pulse width and peak power obtained in this case were 0.19 mJ, 164 ns and 1.16 W respectively.