Power Slope Efficiency Research Articles

Effective Aperture in Periodically Poled Mg-Doped Stoichiometric LiTaO3 for Quasi-Phase-Matched Optical Parametric Oscillation

A two-dimensional mapping method was employed to investigate the homogeneity of optical parametric oscillator (OPO) performance, such as output power distribution, slope efficiency, and oscillation threshold, based on periodically poled 1 mol % Mg-doped stoichiometric LiTaO3 devices fabricated by single and multi-pulse methods. The output power decreased from the electrode-patterned face to the opposite face at low pump intensities and became homogenous over the aperture at high pump intensities. The devices fabricated by the two methods showed no large differences in OPO properties, except for better homogeneity in depth for multi-pulse devices. A large effective aperture (fluctuation < 10%) of 1.4×1.3 mm2 was obtained in both types of devices.

Highly efficient optically pumped cesium vapor laser

We have demonstrated an optically pumped continuous wave Cs vapor laser with an input power to output power slope efficiency of 81%. The laser power was 0.35W for an input power of 0.57W, yielding an overall optical efficiency of 63%.

극초단 펄스 Cr4+:YAG 레이저의 제작 및 동작 특성

1.064 <TEX>$\mu\textrm{m}$</TEX> 파장의 연속발진 Nd:YAG 레이저를 펌핑 광원으로 하여 적외선 영역에서 광대역으로 파장 가변되는 연속발진 및 극초단펄스 C <TEX>$r^{4+}$</TEX> :YAG 레이저를 자체 제작하였다. C <TEX>$r^{4+}$</TEX> :YAG 레이저의 연속발진 및 펄스의 출력특성과 파장 가변 영역은 다음과 같다. 연속발진일 경우 1.436 <TEX>$\mu\textrm{m}$</TEX>에서 600 mW의 평균출력을 보였으나, 복굴절 필터를 삽입했을 경우는 1.492 <TEX>$\mu\textrm{m}$</TEX>근처에서 400 mW의 평균출력을 보였다. 펄스발진일 경우 1.436 <TEX>$\mu\textrm{m}$</TEX>에서 최초로 평균출력 320 mW의 모드록킹된 펄스가 발생하였지만 물 흡수대의 영향으로 불안정함을 피할 수 없었다. 따라서, 복굴절 필터를 사용하여 중심파장을 1.492 <TEX>$\mu\textrm{m}$</TEX>로 이동시켰으며 이 영역에서 안정한 상태의 모드록킹된 43 fs의 극초단 펄스를 생성하였다. 이 때의 평균출력은 280 mW이고, 반치폭(FWHM)은 45 nm이었다. We have developed a mode-locked ultra-short pulse C <TEX>$r^{4+}$</TEX>:YAG laser, as well as a continuous wave C <TEX>$r^{4+}$</TEX>:YAG laser. The laser was pumped by a Nd:YAG laser and its characteristics were investigated. In continuous wave mode, we obtained as much as 600 mW at 1.436 <TEX>${\mu}{\textrm}{m}$</TEX> with pumping power of 6 W, by using an output coupler with a reflectivity of 98%. The power slope efficiency was 10%, when the gain medium was cooled to 19<TEX>$^{\circ}C$</TEX>. The tuning range was varied from 1.39 <TEX>${\mu}{\textrm}{m}$</TEX> to 1.55 <TEX>${\mu}{\textrm}{m}$</TEX> and the maximum power was 400 mW at 1.492 <TEX>${\mu}{\textrm}{m}$</TEX> with a 3-plate birefringent filter. The C <TEX>$r^{4+}$</TEX>:YAG laser was mode-locked by a Kerr lens mode locking method. Mode locking at 1.436 <TEX>${\mu}{\textrm}{m}$</TEX>was initiated by slightly rocking a mirror mount. But the pulses were very unstable because of the strong water absorption at this region. So we shifted the lasing wavelength to 1.492 <TEX>${\mu}{\textrm}{m}$</TEX> by using a 3-plate birefringent filter. Then we obtained stable state mode-locking with the maximum average power of 280 mW for a pumping power of 6 W. The pulse width of 43 fs was measured using an autocorrelator and the repetition rate was 104.5 MHz.

Erbium-implanted high-Qsilica toroidal microcavity laser on a silicon chip

Lasing from an erbium-doped high-Q silica toroidal microcavity coupled to a tapered optical fiber is demonstrated and analyzed. Average erbium ion concentrations were in the range 0.009–0.09 at. %, and a threshold power as low as 4.5 µW and an output lasing power as high as 39.4 µW are obtained from toroidal cavities with major diameters in the range 25–80 µm. Controlling lasing wavelength in a discrete way at each whispering-gallery mode was possible by changing the cavity loading, i.e., the distance between the tapered optical fiber and the microcavity. Analytic formulas predicting threshold power and differential slope efficiency are derived and their dependence on cavity loading, erbium ion concentration, and Q factor is analyzed. It is shown that the experimental results are in good agreement with the derived formulas.

Terahertz quantum-cascade lasers based on an interlaced photon-phonon cascade

A THz (λ∼80 μm) quantum-cascade laser utilizing alternating photon- and phonon-emitting stages has been developed to achieve efficient extraction of electrons from the lower laser level. Thermal backfilling of electrons is drastically reduced leading to an operation up to 95 K and a weak temperature dependence of the power versus current slope efficiency. The threshold current density is 280 A cm−2 at 6 K and increases to 580 A cm−2 at 90 K. Peak output powers of 10 mW at 30 K and 4 mW at 80 K are obtained.

High-power, low-noise, Yb-doped, cladding-pumped, three-level fiber sources at 980 nm.

We present results on a high-power, cladding-pumped, Yb-doped fiber emitting at 977 nm in laser and ampllified-spontaneous-emission source configurations. We obtained up to 1.4 W of fiber-coupled, single-mode output power and slope efficiency as high as 68%. To our knowledge these are the highest powers efficiencies achieved from a single-mode fiber laser at approximately 980 nm and the first demonstrated results on a high-power amplified-spontaneous-emission source in this wavelength range. High power and high slope efficiency are achieved by using a high numerical aperture (> 0.7), a jacketed air-clad fiber, and a high-brightness pump source. Both types of sources exhibit relative intensity noise below -130 dB/Hz and are thus suitable for a wide range of applications.

Tapered waveguide with parabolic lens: theory and experiment

Theoretical and experimental work to integrate parabolic intracavity lens into a high-power tapered ridge-waveguide semiconductor laser diode is carried out. A finite difference beam propagation model is used to simulate the laser operation with and without the lens. Focused ion-beam etching is used to integrate the lens with the laser cavity. The lens is designed to compensate for the phase curvature of the incident mode on the output facet. This leads to improved linearity in the light-current characteristics of the device, showing an increase of up to 47% in power slope efficiency, 2-μm broadening in near field pattern, and 1-deg narrowing in the far-field pattern.

Continuous-wave power performance of a 2.47-/spl mu/m Cr/sup 2+/:ZnSe laser: experiment and modeling

Power performance of a continuous-wave Cr/sup 2+/:ZnSe laser was investigated experimentally and numerically at 2.47 /spl mu/m. In the experiments, an astigmatically compensated z-cavity with a 3% transmitting output coupler produced as high as 250 mW of output power when excited by a NaCl:OH/sup $/color-center laser at 1.58 /spl mu/m. The measured absorbed power slope efficiency was 24.2%. Experimental pump absorption saturation and laser efficiency data were analyzed by using a numerical model to determine the absorption, emission, and excited-state absorption cross-sections. Simulations were then performed to investigate the dependence of the output power on crystal and resonator parameters. Results indicate that optimum power performance should be obtained with a 1.5-cm-long crystal which has a total unsaturated absorption of 86%. Finally, the optimum output coupling of the resonator was determined to be 10%.

Intracavity lens for low-divergence high-power laser diode operation

An intracavity lens has been integrated into a high-power tapered ridge-waveguide semiconductor laser diode. The lens is designed to compensate for the phase curvature of the incident mode on the output facet. This has led to improved linearity in the light–current characteristics of the device, showing an increase of up to 47% in power slope efficiency and a reduction of up to 17% in the full width at e−2 intensity of the far field pattern.

Efficient grating-tuned mid-infrared Cr^2+:CdSe laser

Room-temperature, all-solid-state, broadly tunable laser operation of Cr(2+) -doped CdSe has been demonstrated. Pumping with a Q -switched Tm, Ho:YLF laser running at a 1-kHz repetition rate achieved broadband output of 500 mW at 2.6 microm with 48% absorbed power slope efficiency. With reduced efficiency, as much as 815 mW of power was obtained. With a diffraction grating, the Cr(2+): CdSe laser was tuned from 2.3 to 2.9 microm with 10-nm bandwidth (FWHM) and output power up to 350 mW.

Efficient continuous-wave operation of a diode-pumped Nd:YVO 4 laser at 1342 nm

The experimental study described in this paper investigates the continuous-wave power performance of an efficient diode-pumped Nd:YVO 4 laser at 1342 nm by employing four different end pumping configurations. When pumped by a high-power fiber-coupled diode array at 806 nm, the compact resonator consisting of a 9.25-mm long Nd:YVO 4 crystal and a 3.6% transmitting output coupler produced as high as 3550 mW of output power. The absorbed power slope efficiency was measured to be 28.1%. By using the experimentally measured threshold data, the stimulated emission cross-section of the gain medium was determined to be 13×10 −19 cm 2 at 1342 nm. Above absorbed pump powers of 11 W, strong thermal loading caused saturation of the output power and the focal length of the induced thermal lens was measured as a function of the pump power. Results further showed that the laser output was insensitive to variations in the crystal boundary temperature between 20°C and 40°C.

Continuous-wave broadly tunable Cr^2+:ZnSe laser

We report room-temperature operation of an all-solid-state broadly tunable continuous-wave Cr(2+):ZnSe laser. Output power of 250 mW, an absorbed power slope efficiency of 63%, and continuous tunability from 2138 to 2760 nm are demonstrated.

Calculation of optical power emitted from a fibre grating laser

The optical power that can be obtained from the facets of a fibre grating laser is calculated in the paper. This calculation is based on the effective transmission coefficient of the compound cavity of the device. The dependence of slope efficiency (of power per facet) on the reflectivities of the diode facets and grating, length of the laser diode and grating, and emission wavelength are considered. A configuration is suggested which allows the largest amount of optical power to be obtained from the back facet of the device when fibre gratings with strong reflectivities are used. It is also shown that a reduction in facet reflectivity results in significant reduction of the variation of output power slope efficiency due to changes in emission wavelength or length of the external cavity.

Efficient continuous-wave radiatively cooled Cr^4+:forsterite lasers at room temperature

Results of a detailed experimental investigation aimed at reducing the thermal loading problem in a cw Cr(4+):forsterite laser at elevated temperatures are presented. From a Cr(4+):forsterite crystal with a differential absorption coefficient of 0.57 cm(-1), as much as 900 mW of cw output power has been obtained at 1.26 mum and at a crystal boundary temperature of 15 degrees C with an absorbed pump power of only 4.5 W at 1.06 mum. No chopping of the pump beam was necessary. An efficient radiative cooling technique was further employed to cool the laser and no subsequent power fading was observed. To the author's knowledge, the measured absorbed power slope efficiency of 29.5% represents the highest cw power performance reported to date from a Cr(4+):forsterite laser pumped by a Nd:YAG laser around room temperature. The role of the low differential absorption coefficient in the reduction of thermal loading is further elucidated by presenting comparative cw power performance data with a second Cr(4+):forsterite crystal having a differential absorption coefficient of 1.78 cm(-1) in the temperature range between 12 and 35 degrees C. Finally, some interesting multipulse effects of the laser observed in the millisecond regime during quasi-cw operation at 50% duty cycle are described.

Efficient continuous-wave chromium-doped YAG laser

Continuous-wave power performance of a chromium-doped YAG laser pumped by a Nd:YAG laser is investigated as a function of crystal temperature, output coupling transmission, and emission wavelength. Using a 2%-transmitting output coupler, we obtained as much as 1.9 W of cw output power at 1.45 μm with an absorbed power slope efficiency of 42% when the gain medium was cooled at 3°C. Using the laser efficiency data, we estimated the emission and excited-state absorption cross sections at 1.45 μm and compared them with the previously reported values.

High-power visible upconversion laser

Laser output power approaching 0.5 W cw has been obtained at 551 nm by using upconversion pumping of YLiF4:Er 5%. A power slope efficiency of 14% has been determined, and the output coupling for the available pump power has been optimized at 797 nm.

Highly tunable and efficient diode pumped operation of Tm3+doped fibre lasers

The characteristics of a Tm3+ doped fibre laser pumped by a laser diode are reported. Operating at a wavelength of 1.94 μm, the laser had a threshold of 4.4 mW, a launched power slope efficiency of 17% and 1 mW output power. Measurements on the tuning range of Tm3+ are presented and lasing is found to be possible from 1.65–2.0 μm, the specific range depending on the fibre type. The largest range for a single laser was 300 nm.

CW laser pumped emerald laser

A CW laser pumped emerald laser is reported, A 34 percent output power slope efficiency is observed with longitudinal pumping by a krypton laser in a nearly concentric cavity. The laser has been tuned from 728.8 to 809.0 nm, Losses in emerald are larger than those of alexandrite determined in a similar cavity. Our data also indicate that the excited state absorption minimum is shifted from that of alexandrite.

High efficiency cw laser-pumped tunable alexandrite laser

High efficiency cw alexandrite laser operation has been achieved. With longitudinal pumping by a krypton laser in a nearly concentric cavity, a 51% output power slope efficiency has been measured. Including the transmission at the input coupler mirror, a quantum yield of 85% has been attained above threshold. Tunability from 726 to 802 nm has also been demonstrated. The low loss and good thermal properties make alexandrite ideal for cw laser operation.