Comparison of <Emphasis Type="Italic">c</Emphasis>-Nd:YVO<Subscript>4</Subscript>/YVO<Subscript>4</Subscript> raman lasers and <Emphasis Type="Italic">c</Emphasis>-Nd:YVO<Superscript>4</Superscript> self-Raman lasers

Raman lasers based on c-Nd:YVO₄ crystals can generate 1178 nm Stokes line, which can be frequency-doubled to realize 589 nm sodium lasers. We make comparative experimental studies of c-Nd:YVO₄/YVO₄ Raman lasers and c-Nd:YVO₄ self-Raman lasers. About these two kinds of lasers, the output characteristics of power, center wavelength and beam quality are measured and compared.     

Efficient continuous-wave YVO<Subscript>4</Subscript>/Nd:YVO<Subscript>4</Subscript> Raman laser at 1176 nm

We present a simple and compact continuous-wave (CW) 1176 nm laser based on self-frequency Raman conversion in continuous-grown YVO₄/Nd:YVO₄ composite crystal. With a composite crystal 30 mm in length, a maximum output power up to 1.84 W was achieved at the incident diode pump power of 23.6 W. Corresponding to overall optical conversion, the efficiency was 7.8% and the slope efficiency was 8.5%. The conversion efficiency has been doubled compared with the conventional Nd:YVO₄ CW self-frequency Raman laser. The excellent performance of this laser shows that the long continuous-grown YVO₄/Nd:YVO₄ composite crystal is promising in the application of CW Raman lasers and ideal for miniaturization.     

A comprehensive study of Nd:YAG, Nd:YAlO3, Nd:YVO4 and Nd:YGdVO4 lasers operating at wavelengths of 0.9 and 1.3 μm. Part 1: cw-operation

This paper reports on efficient generation of cw laser radiation at 0.9 and 1.3 μm in different neodymium doped laser hosts. The thermal, mechanical and optical properties as well as the laser performance of Nd:YAG, Nd:YAlO₃, Nd:YVO₄ and Nd:GdVO₄ are studied in numerical simulations as well as in experimental investigations. For example an output power of more than 4.0 W is generated in Nd:YVO₄ at the 914 nm ⁴F_3/2→⁴I_9/2 transition using a pump power of 19 W. In Nd:GdVO₄ more than 6.0 W are obtained at the 1342 nm ⁴F_3/2→⁴I_13/2 laser transition by using a pump power of 19.3 W. The spatial beam quality of both lasers is diffraction limited with an M² value of less than 1.1. PACS  42.70.Hj; 42.55.Xi; 42.60.Pk     

High-power non-astigmatic TEM<Subscript>00</Subscript> and vortex mode generation in a compact bounce laser design

A novel design of a diode-side-pumped bounce amplifier laser is described that can produce a high-power TEM₀₀ mode and Laguerre–Gaussian (LG) vortex mode operation with high circularity and low astigmatism. The design utilises control of pump size and bounce angle such that the laser mode experiences substantially circular symmetric gain and spherical thermal lensing, in a highly compact fundamental mode resonator. In a simple plane–plane Nd:YVO₄ laser resonator with no other optical components and total length of just 13.4 cm, highly circularised TEM₀₀ operation is produced at wavelength 1064 nm, with 14.2 W of power and high beam quality M ²<1.05. Stable Q-switched TEM₀₀ operation is demonstrated up to 900 kHz and second harmonic power of 7.2 W at 532 nm is generated with conversion efficiency up to 64%. Minor modification of the design to exploit the spherical aberration of the thermal lens is shown to allow for generation of a doughnut-shaped LG vortex mode with average power 16.6 W, maintaining extremely low astigmatism. Q-switched operation of the vortex mode is accomplished up to 400 kHz. A detailed numerical thermal analysis of the amplifier design is performed and gives quantitative agreement with experimental results.     

Output power and intracavity intensity profiles of a quasi-continuous end-pumped Nd:YVO4 self-Raman mini laser

The paper presents experimental investigation and modeling of an end-pumped quasi-continuous-wave YVO₄/Nd:YVO₄ mini self-Raman laser. The dependence of the Stokes output power on the pump power in the range from 3 to 17.5 W has been measured. As much as 1.76 W of an average Stokes power, corresponding to a total optical-to-optical conversion efficiency of about 10%, has been obtained. The transverse profiles of the laser (at the fundamental wavelength) and the Stokes beam intensity have been recorded at the output mirror and in the vicinity of the boundary between the pure and Nd-doped parts of the Raman crystal. These distributions have been approximated by the sum of Gaussian and super-Gaussian distributions with corresponding weights. We propose a model of such lasers that takes into account the features of intracavity self-frequency Raman conversion in lasers with highly inhomogeneous non-Gaussian spatial distributions of the pump, laser, and Stokes beam intensity in the cavity. The results of modeling are in good agreement with the experimental data.     

High-power 888-nm-pumped Nd:YVO4 1342-nm oscillator operating in the TEM00 mode

We report on a high-power 888-nm-pumped continuous-wave Nd:YVO₄ laser at 1342 nm. An output power of 24 W emitted into a diffraction limited beam with an M ² parameter better than <1.1 is demonstrated. At an absorbed pump power of 84 W the optical conversion efficiency is 29%.     

Characterization of laser processing of single‐crystal natural diamonds using micro‐Raman spectroscopic investigations

The application of lasers for processing diamond has revolutionized the diamond industry and its applications in microelectronics, microelectromechanical system (MEMS) and microoptoelectromechanical system (MOEMS) technologies. The process quality can be evaluated using spectroscopic techniques. In the present investigation, four different types of Q‐switched solid‐state lasers (with different beam parameters), namely, a lamp‐pumped Nd:YAG laser operating at 1064 nm, a lamp‐pumped Nd:YAG laser operating at second harmonically generated 532 nm, a diode‐pumped Nd:YVO₄ laser operating at 1064 nm and a diode‐pumped Nd:YAG laser operating at 1064 nm, have been employed for the processing of a single‐crystal, gem‐quality, natural diamond. The main objective behind the selection of these lasers with different beam parameters was to study the effect of wavelength, pulse width, pulse energy, peak power and beam quality factor (M² factor) on various aspects of processing (such as microcracking, material loss and cut surface quality) and their relative merits and demerits. The overall weight loss of the diamond and formation of microcracks during processing have been studied for the above four cases. The characteristics of the graphite formed during processing, elemental analysis, surface morphology of the cut surface and process dynamics have been studied using micro‐Raman spectroscopy and scanning electron microscopy (SEM). We observed that laser cutting of single‐crystal diamonds used for industrial applications can be accomplished without microcracking or surface distortion using Q‐switched Nd:YAG lasers. This allows direct processing without extensive postgrinding and polishing stages. Very efficient diamond processing is possible using diode‐pumped lasers, which results in the lowest possible breakage rate, good accuracy, good surface finish and low weight loss. From the micro‐Raman and SEM studies, it is concluded that the surface quality obtained is superior when diode‐pumped Nd:YVO₄ laser is used, owing to its extremely high peak power. The maximum graphite content is observed while processing with lamp‐pumped Nd:YAG laser at 532 nm. An overall comparison of all the laser sources leads to the conclusion that diode‐pumped Nd:YAG laser is a superior option for the efficient processing of natural diamond crystals. Copyright © 2006 John Wiley & Sons, Ltd.     

Millijoule intracavity OPO driven by a passively Q-switched Nd:YVO<Subscript>4</Subscript> laser with AlGaInAs quantum-well saturable absorber

We originally demonstrate the use of an AlGaInAs periodic quantum-well absorber to achieve a quasi-continuous-wave (QCW) diode-pumped passively Q-switched Nd:YVO₄ laser with an intracavity optical parametric oscillator (OPO). With a diode-pumping energy of 35 mJ, the output pulse energy and the pulse width at 1573 nm are found to be 1.58 mJ and 26 ns, respectively. The pulse repetition rate can be up to 100 Hz with the overall OPO beam quality M² factor to be better than 1.5.     

A novel orthogonally linearly polarized Nd:YVO4 laser

We presented a novel orthogonally linearly polarized Nd:YVO₄ laser. Two pieces of a-cut grown-together composite YVO₄/Nd:YVO₄ crystals were placed in the resonant cavity with the c-axis of the two crystals orthogonally. The polarization and power performance of the orthogonally polarized laser were investigated. A 26.2-W orthogonally linearly polarized laser was obtained. The power ratio between the two orthogonally polarized lasers was varied with the pump power caused by the polarized mode coupling. The longitudinal modes competition and the corresponding variable optical beats were also observed from the orthogonally polarized laser. We also adjusted the crystals with their c-axis parallele to each other, and a 40.7-W linearly polarized TEM₀₀ laser was obtained, and the beam quality factors were M²_x=1.37 and M²_y=1.25.     

High efficiency continuous-wave single-frequency Nd:YVO<Subscript>4</Subscript> ring laser under diode pumping at 880 nm

An efficient single-frequency continuous-wave Nd:YVO₄ ring laser pumped at 880 nm is presented. With compact four-mirror ring cavity and optical isolator, we obtained an output power of 14.56 W at 1064 nm, corresponding to a slope efficiency of 61.7% and an optical-to-optical efficiency of 58.4% with respect to the absorbed pump power. The stability of the output power was better than ±0.5% over two hours. At the same time, a beam quality factor of M ²≈1.2 was measured and the line width of the longitudinal mode was about 25 MHz. To the best of our knowledge, this is the highest slope efficiency and optical-to-optical efficiency in single-frequency Nd:YVO₄ ring laser.     

High power modelocking of a stigmatic bounce geometry laser using a nonlinear mirror

We report the highest average power modelocking of a novel bounce geometry laser using the nonlinear mirror (NLM) technique. A diode-side pumped Nd:YVO₄ slab lasing at 1064 nm in a spatially stigmatic bounce-oscillator configuration was modelocked using a type-I phase-matched BiBO nonlinear crystal (NLC) in a NLM arrangement, producing 12 W of self-starting, continuous-wave (CW) modelocking. The system produced a pulse duration of 14 ps at a repetition rate of 110 MHz with high long-term stability and excellent beam quality, with an M ²<1.2 and highly circular beam profile. An investigation was made of the sensitivity of modelocking as a function of air dispersion, by varying the distance between the NLC and output coupler. No optical damage was observed throughout the investigation, even when the system was operated in Q-switched modelocking regime. The system exploits the advantages of NLM modelocking for sustaining high average and peak powers without the onset of optical damage.     

High-power Nd:YVO4/BaWO4 intracavity Raman laser emitting at 1,103?nm

A compact BaWO₄ Raman laser is realized with a diode-end-pumped acousto-optically Q-switched YVO₄/Nd:YVO₄ laser. Based on the Raman shift at 332?cm^?1 of BaWO₄, first-Stokes generation at 1,103?nm is generated. At a pump power of 11.3?W and a repetition rate of 45?kHz, an average power of 1.59?W is obtained. The pulse width is measured to be 36.8?ns and the beam quality factor (M ²) in the horizontal and vertical directions is determined to be 1.56?±?0.1 and 1.41?±?0.1, respectively. The thermal focal lengths of the laser medium and Raman medium are calculated theoretically.     

Efficient diode-pumped Nd:YVO4 continuous-wave laser at 1.34 μm

We report a high-power continuous-wave(cw) diode-pumped efficient 1.34 μm Nd:YVO₄ laser. The laser properties of a low Nd³⁺-doped concentration of the Nd:YVO₄ crystal operating at 1.34 μm formed with a simple plane-concave cavity have been demonstrated. With the incident pump power of 22 W, an output power of 8.24 W was obtained, giving an optical conversion efficiency of 37.5% and slope efficiency of 40%. The thermal effects of cw end-pumped solid-state lasers were studied.     

Advances in vanadate laser crystals at a lasing wavelength of 1 micrometer

Sapphire, garnet and vanadate crystals are the most prominent optical materials, and vanadates play important roles in optics, especially in lasers and nonlinear optics. Neodymium‐doped yttrium vanadate (Nd:YVO₄) is representative and available commercially. Based on Nd:YVO₄, several vanadate crystals are being developed with the goal of fulfilling the need for differential applications and improvement of certain operational aspects, such as with pulsed lasers or high‐power continuous‐wave lasers. In recent years, some important effects, including energy enhancement, bistability of output performance, self‐Raman frequency shifting, etc., and some novel applications, such as quantum optics, pulsed lasers modulated by the two‐dimensional crystals, etc., have been discovered with vanadates as gain materials. In this paper, the preparation, characterization and laser applications of vanadate laser crystals at the lasing wavelength of 1 micrometer, including YVO₄, GdVO₄, LuVO₄, Gd_xY_1–xVO₄ and Lu_xGd_1–xVO₄ (0 < x < 1) doped with Nd³⁺ and ytterbium (Yb³⁺) are systematically reviewed by highlighting the most recent research progress. Their specific properties are presented, generation mechanisms of novel physical effects are discussed, new applications are given and possible future applications proposed by focusing on some potential strengths.     

High peak power 16 μm InP-related quantum cascade laser

In this paper ～16 μm-emitting multimode InP-related quantum cascade lasers are presented with the maximum operating temperature 373 K, peak and average optical power equal to 720 mW and 4.8 mW at 303 K, respectively, and the characteristic temperature (T₀) 272 K. Two types of the lasers were fabricated and characterized: the lasers with a SiO₂ layer left untouched in the area of the metal-free window on top of the ridge, and the lasers with the SiO₂ layer removed from the metal-free window area. Dual-wavelength operation was obtained, at λ ～ 15.6 μm (641 cm^?1) and at λ ～ 16.6 μm (602 cm^?1) for lasers with SiO₂ removed, while within the emission spectrum of the lasers with SiO₂ left untouched only the former lasing peak was present. The parameters of these devices like threshold current, optical power and emission wavelength are compared. Lasers without the SiO₂ layer showed ～15% lower threshold current than these ones with the SiO₂ layer. The optical powers for lasers without SiO₂ layer were almost twice higher than for the lasers with the SiO₂ layer on the top of the ridge.     

Vector polarization effect appearing in tensor polarized beams of nuclei under channeling conditions and during measurements of the quadrupole moments of unstable nuclei

General relations describing the spin dynamics of beams of nuclei with initial tensor and vector polarizations have been derived upon planar channeling in bent crystals. The performed analysis indicates that the vector polarization effect predicted by Baryshevsky and Sokolsky can be detected, occurring upon the planar channeling of a beam of nuclei with initial tensor polarization. The planar channeling of a beam of nuclei with initial tensor and vector polarizations can be used to determine the quadrupole moments of unstable nuclei with small lifetimes, up to 10⁻⁷ s. The quadrupole moments of nuclei with lifetimes of about 10⁻⁷ s cannot be measured via known methods, including optical methods.     

A comprehensive study of Nd:YAG,Nd:YAlO<Subscript>3</Subscript>, Nd:YVO<Subscript>4</Subscript> and Nd:YGdVO<Subscript>4</Subscript> lasers operating at wavelengths of 0.9 and 1.3 μm. Part 2: passively mode locked-operation

This paper reports on the generation of picosecond (ps) laser pulses by self-phase-adjusting additive-pulse-mode-locking (PSA) at wavelengths of 0.9 and 1.3 μm. The main objective of this work was to investigate and compare the characteristic optical properties of ps lasers based on different Nd-doped laser crystals like Nd:YAG, Nd:YAlO₃, Nd:YVO₄ and Nd:GdVO₄. As a result of these investigations a mode-locked Nd:YVO₄ laser for example, generated, ps pulses at 1.3 μm with a duration of 7 ps, a repetition rate of 160 MHz and an average power of 4.7 W. At 0.9 μm pulses with a duration of 1.9 ps were obtained at a repetition rate of 158 MHz and an average power of 2.8 W. PACS  42.70.Hj; 42.65.Re; 42.65.Ky     

Comparison between c-cut and a-cut Nd:YVO4 lasers passively Q-switched with a Cr4+:YAG saturable absorber

Comparison between c-cut and a-cut Nd:YVO₄ microchip lasers passively Q-switched with a Cr⁴⁺:YAG saturable absorber is experimentally made. The lower emission cross section of the c-cut Nd:YVO₄ crystal can enhance the passive Q-switching effect to produce a peak power 10 times higher than that obtained with the a-cut crystal. The experimental result further reveals that a c-cut Nd:YVO₄ crystal is a very convenient material for short-pulse (sub-nanosecond) and high-peak-power (>10 kW) lasers. Received:10December2001/Revisedversion:22January2002 / Published online: 14 March 2002     

Continuous-wave intracavity Raman laser at 1179.5 nm with SrWO<Subscript>4</Subscript> Raman crystal in diode-end-pumped Nd:YVO<Subscript>4</Subscript> laser

We report a continuous-wave intracavity Raman laser at 1179.5 nm with a SrWO₄ Raman crystal in a diode-end-pumped Nd:YVO₄ laser. The highest output power of 2.23 W is obtained at the laser diode power of 21.2 W corresponding to the slope efficiency of 17.3% and a diode-to-stokes optical conversion efficiency of 10.5%. The dependence of the Raman laser performance on the pump polarization is also studied. The measured Raman thresholds are about 9.3 and 8.3 W in the diode pump laser power for the a- and b-polarized configurations, respectively. The Raman gain coefficients of the c-cut SrWO₄ crystal for a- and b-polarized pumps are estimated to be about 4.9 and 4.7 cm/GW, respectively.     

Raman scattering from confined phonons in GaAs/AlGaAs quantum wires

We report on photoluminescence and Raman scattering performed at low temperature (T =  10 K) on GaAs/Al_0.3Ga_0.7As quantum-well wires with effective wire widths ofL =  100.0 and 10.9 nm prepared by molecular beam epitaxial growth followed by holographic patterning, reactive ion etching, and anodic thinning. We find evidence for the existence of longitudinal optical phonon modes confined to the GaAs quantum wire. The observed frequency at ο_L10 =  285.6 cm⁻¹forL =  11.0 nm is in good agreement with that calculated on the basis of the dispersive dielectric continuum theory of Enderleinas applied to the GaAs/Al_0.3Ga_0.7As system. Our results indicate the high crystalline quality of the quantum-well wires fabricated using these techniques.