Comparison between shared and coupled resonators for passively Q-switched Nd:GdVO4 intracavity optical parametric oscillators

Comparison between the shared and coupled resonators for the intracavity optical parametric oscillators pumped by passively Q-switched Nd:GdVO₄ lasers is experimentally made. The shared and coupled resonators are found to be complementary in the performances of the pulse repetition rate, pulse duration and pulse energy. It is also found that the output signal pulses of the shared cavity explicitly display the mode-locking phenomenon. On the whole, the amplitude stability of the shared cavity configuration is substantially superior to that of the coupled cavity configuration. PACS 42.60.Gd; 42.65.Yj; 42.55.Xi     

高功率激光器腔镜热变形对输出光束质量的影响

利用有限元分析法结合Fox-Li迭代法,考虑腔内本征模式与腔镜热形变的相互耦合作用,计算模拟了正支共焦非稳腔的本征模式分布,定量分析了高功率激光器腔镜热变形对输出光束质量的影响,重点讨论了腔镜热变形所引起的腔内本征模式相位特性的变化,并从波前功率谱密度、Zernike像差系数及光束质量值等角度对腔镜发生热形变前后的激光器输出光束的光束特性进行比较分析。研究结果表明:高功率激光器腔镜热形变对输出光束的光束质量会产生一定的影响,且随着激光输出功率的增大,镜面热形变引起的输出光束波前相位高频比例及Zernike高阶像差均会有所增大,波前畸变程度也明显变大,光束质量逐渐变差。     

Nd:KGW/KGW crystal: efficient medium for continuous-wave intracavity Raman generation

Diode pumped continuous-wave intracavity Raman conversion in a composite Nd:KGW/KGW crystal has been investigated. The use of a Nd:KGW/KGW crystal instead of the ordinary Nd:KGW crystal has made it possible to considerably decrease intracavity losses. A Raman threshold corresponding to a diode laser power of 230 mW and a quantum efficiency of conversion of diode laser radiation to the Stokes radiation of 22% have been obtained. PACS 42.55.Rz; 42.55.Xi; 42.55.Ye     

Influence of unstable cavity optical component aberrations on laser beam divergence

Based on the geometrical optics approximation, the influences of some optical component aberrations of confocal unstable resonators on the laser beam divergence are discussed. The explicit dependence of the laser beam divergence on the cavity magnification, the structure of the mirror defects, the mirror curvature radii and the tilting angle of intracavity windows are given for both positive- and negative-branch resonator configurations.ENEA guest and with Electronic Engineering (EL.EN), Florence, Italy.     

Single-frequency cw vertical external cavity surface emitting semiconductor laser at 1003 nm and 501 nm by intracavity frequency doubling

This work reports single-frequency laser oscillation at λ=1003.4 nm of a diode-pumped vertical external cavity surface-emitting semiconductor laser for metrological applications. A low thermal resistance of the semiconductor active component is achieved by solid-liquid interdiffusion bonding onto a SiC substrate. The spectro-temporal dynamics of the laser is theoretically studied. Experimentally, an output power of 1.7 W is demonstrated in free running operation, and up to 500 mW in a true single longitudinal mode. Furthermore, single-frequency laser emission at λ=501.7 nm is obtained by intracavity frequency doubling, resulting in a total output power as high as 62 mW. PACS 42.55.Px; 42.55.Xi; 42.62.Eh; 42.65.Ky     

Diode-pumped Q-switched laser with intracavity sum frequency mixing in periodically poled KTP

We report on a diode pumped Q-switched yellow-orange laser, with intracavity sum-frequency generation, in a periodically poled KTiOPO₄ crystal in a diode-pumped Q-switched dual-wavelength laser at 1064 and 1342 nm. The conversion efficiency is measured as a function of crystal temperature, incident pump power, and pulse repetition rate. Under optimal phase-matching conditions, the highest yellow-orange average power was 610 mW at a pump power of 17 W. PACS 42.60.Gd; 42.55.Rz; 42.55.Xi     

Diode-pumped distributed-feedback dye laser with an organic–inorganic microcavity

We present a diode-pumped microcavity dye laser composed of a top organic reflector and a bottom inorganic reflector. The top organic reflector consists of alternate thin films of cellulose acetate and poly(N-vinylcarbazole) doped with coumarin 540A to construct a distributed-feedback (DFB) resonator. Pumped directly by an InGaN-based blue laser diode (LD) with a pulse duration of 4 ns, the microcavity dye laser exhibited a single-mode oscillation at 563 nm with a threshold pump LD power of 290 mW/pulse. The emission of the microcavity dye laser was measured through an optical fiber, resulting in a peak power of 2.5 mW for a pump LD power of 320 mW. PACS  42.55.Mv; 42.55.Sa; 42.55.Xi     

Spectroscopic properties and amplified spontaneous emission of a new derivative of fluorescein

The new laser dye, 2-(6-acryloyloxy-3-oxo-3H-xanthen-9-yl)-benzoic acid ethyl ester [AOXBE] has been synthesized. Its chemical structure was confirmed by ¹HNMR, IR, MS and elemental analysis. This new dye was covalently bonded with methyl methacrylate (MMA) and 2-hydroxy ethyl-methacrylate (HEMA) copolymer backbone. Its optical properties were experimentally investigated. Amplified spontaneous emission (ASE) and photostability were studied by pumping the dye polymeric sample with a 355 nm (8 ns) pulsed Nd:YAG laser. PACS 42.55.Mv; 42.70.Hj; 42.70.Jk; 42.55.Px     

Diode-pumped lasers for ultra-high peak power

The generation of the highest laser peak intensities at a high degree of system compactness can be achieved by combining modern diode-pump technologies with the chirped pulse amplification technique. In principle, the spectroscopic properties of the gain medium determine the scaling laws of both high output pulse energy and short pulse duration. Here we introduce a novel criterion classifying laser materials with respect to their ability to generate pulses of highest peak power in a diode-pumped solid state laser system. Furthermore, amplified spontaneous emission as well as laser damage issues affecting the efficiency and compactness of a laser amplifier system are discussed. PACS 42.55.Ah; 42.55.Xi; 42.70.Hj     

Pulse symmetry and pulse duration compression in a diode-pumped doubly passively Q-switched Nd:YVO4 lasers with Cr4+:YAG and GaAs saturable absorbers

We present a simple technique to improve the symmetry of pulse emitted by doubly passively Q-switched lasers. Using both Cr⁴⁺:YAG and GaAs saturable absorbers in the same cavity, a diode-pumped doubly passively Q-switched Nd:YVO₄ laser is realized for the fist time. This laser can generate more symmetric pulse with shorter pulse width and higher peak power compared with the solely passively Q-switched laser with Cr⁴⁺:YAG saturable absorber or GaAs coupler. The pulse symmetry factor ε of such a doubly passively Q-switched laser is experimentally shown to reach 1.05. Simulations by a rate-equation model for doubly passively Q-switched laser are in close agreement with the experimental results.PACS 42.55.Xi; 42.55.Rz; 42.60.Gd     

A linearly polarized continuous-wave 1357-nm Nd:YAG laser

We demonstrated a linearly polarized continuous-wave Nd:YAG laser operating at a 1357-nm single-wavelength, by a 808-nm diode as an end-pump source. We chose a Brewster-angle-cut Nd:YAG laser host crystal, due to its two salient features as follow: linearly polarized laser output and single-wavelength oscillation can be easily obtained. In this paper, a continuous-wave all-solid-state single-wavelength laser operating at 1357 nm is demonstrated with a diode-end-pumped Brewster-cut Nd:YAG laser. The laser had a 1.03-W maximum output power under an incident pump power of 15.0 W, a 12.7% slope efficiency, a 6.9% optical-to-optical conversion efficiency, a 0.14-nm spectral linewidth and a 3% power-output stability within 30 min. PACS 42.55.Rz; 42.55.Xi; 42.70.Hj     

110 W ceramic Nd<Superscript>3+</Superscript> : Y<Subscript>3</Subscript>Al<Subscript>5</Subscript>O<Subscript>12</Subscript> laser

A high-power, continuous-wave 0.6% Nd³⁺-doped ceramic Y₃Al₅O₁₂ (Nd:YAG) laser has been developed. 110 W laser output at 1064 nm was obtained, with a slope efficiency of about 41%. The M² factor was found to be around 6. The laser performance of the ceramic laser material was found to compare favorably with that obtained with single crystal Nd:YAG. PACS 42.55.-f; 42.55.Xi; 42.70.Hj     

Diode-pumped 200 μm diameter core, gain-guided, index-antiguided single mode fiber laser

Single mode laser action in a diode-pumped gain-guided, index- antiguided Nd³⁺-doped phosphate glass fiber having a 200-μm-diameter core is demonstrated. Near-Gaussian beam quality was maintained, even when pumped up to four times the threshold pump power, indicating robust lowest order mode oscillation. Subtle differences associated with the effectiveness of diode pumping gain-guided, index-antiguided fibers are discussed. PACS 42.55.Wd; 42.55.Xi     

Comparative analysis of Tm-Ho:KYF4 laser crystals

A spectroscopic characterization of Tm-Ho:KYF₄ crystals with different doping levels is presented. A comparative investigation based on diode-pumped 2-μm laser experiments shows that the best trade-off in terms of cw output power characteristics and wavelength tuning ranges is obtained with 5% Tm-0.5% Ho active crystal. PACS 42.55Xi; 42.55Rz; 42.60Pk; 42.70Hj; 42.60Lh     

Two-photon pumping of random lasers by picosecond and nanosecond lasers

We experimentally demonstrated two-photon pumping of random lasers using picosecond and nanosecond pump lasers. The picosecond laser pumping experiment was performed with 400 ps laser pulses at 770 nm, and the gain media was a Coumarin 480D dye solution doped with TiO₂ nanoparticles. Onset of laser action was observed at a pump laser pulse energy below 500 μJ. The nanosecond laser pumping experiment was performed with 7 ns laser pulses at 1064 nm, and the gain media was a Rhodamine 640 dye solution doped with TiO₂ nanoparticles. Onset of laser action was observed at a pump laser energy ∼18 mJ. Our results suggest that there exists an optimal pulse duration of the pumping laser in two-photon pumped random lasing that leads to minimum photodamage of the gain media and still keeps a high pumping efficiency. PACS 33.50.Dq; 42.55.Mv; 42.55.Zz     

High-power picoseconds 355 nm laser by third harmonic generation based on CsB3O5 crystal

We report on the high average power third harmonic generation (THG) of a mode-locked picosecond laser in a CsB₃O₅ (CBO) crystal. The picosecond laser beam at 1064 nm is produced by a home-made 30 W master oscillator power-amplifier (MOPA) Nd:YVO₄ laser system. The maximum THG output at 355 nm is up to 5.4 W. We also investigate the phase matching angle at different temperatures. During high power operation, the temperature of the CBO crystal is set at a high temperature of more than 100 °C. The THG system has shown a fine long-term stability for more than two months of operation. PACS 42.55.Px; 42.55.Rz; 42.70.Mp; 42.70.Nq; 42.65.Ky     

Diode-pumped passively mode-locked Nd:GdVO<Subscript>4</Subscript> laser with a GaAs saturable absorber mirror

We report on a diode end-pumped passively mode-locked Nd:GdVO₄ laser. By using a GaAs wafer simultaneously as the saturable absorber and the output coupler, stable continuous-wave mode locking was achieved. The pulse width was measured to be 18.9 picoseconds at a repetition rate of 370 MHz. The most remarkable property of the laser is that its repetition rate can be changed from 370 MHz to 3.348 GHz by simply changing the cavity length. An average output power of 3.46 W at a 3.348 GHz repetition rate was obtained with a 14 W pump power. To our knowledge, this is the first demonstration of a passively mode-locked Nd:GdVO₄ laser using a GaAs wafer as the saturable absorber. PACS 42.55.Rz; 42.60.Fc; 42.55.Xi.     

Spectral characteristics of a Yb-doped Y<Subscript>2</Subscript>O<Subscript>3</Subscript> ceramic laser

We report the experimental observation of random wavelength emission and intensity-dependent central-wavelength shift in a diode-pumped Yb³⁺-doped Y₂O₃ ceramic laser. We show experimentally that, like conventional lasers, the emission of the laser has fixed well-defined transverse modes; however, its instantaneous emission wavelengths change randomly with time. The central wavelength of the laser emission also shifts with the intracavity light intensity. A model was developed to describe the spectral behavior of Yb³⁺-doped lasers. We show that the observed random wavelength emission and central lasing wavelength shift of the laser could be well explained based on the strong reabsorption of light in the gain medium. PACS 42.55.Rz; 42.60.Mi; 42.55.Xi     

Efficient noise suppression of an amplified diode-laser by optical filtering and resonant optical feedback

We present the noise suppression of an amplified diode laser by using an optical filter and resonant optical feedback. The intensity noise of the amplified diode laser has been significantly decreased by using the optical filter cavity. It was further suppressed and reached the shot noise limit at 15 MHz by introducing resonant optical feedback from the transmission of the filter cavity. The filter cavity transmits 53% of injection power, and the output power of the filter cavity is more than 200 mW. The observed frequency fluctuations were less than 100 kHz in one minute. This level of noise suppression and output power may allow diode lasers to be utilized in many quantum-optics experiments. PACS 42.55-f; 42.55-Px; 42.50.-p     

Laser operation at high repetition rate of 100 kHz in Nd:GdVO4 under 879 nm diode-laser pumping

Highly efficient continuous-wave and acousto-optically Q-switched laser emission in Nd:GdVO₄ crystal, end-pumped at 879 nm into the laser emitting level, are reported. A maximum cw output power of 13.3 W is obtained, corresponding to the slope efficiency of 74.6% in absorbed power; an average output power of 12.1 W, a pulse width of 20.3 ns and a peak power of about 6 kW are reached at 100 kHz in A-O Q-switched operation. PACS  42.55.-f; 42.55.Xi; 42.60.Gd