High-power solid-state lasers with unstable resonators

The thermal lensing properties of stable and unstable resonators are compared and rules are given for the design of optimized unstable resonators containing a focusing rod. Experimental verification with a high-power Nd: YAG system proved that for unstable resonators the restricting relationship between beam quality and output power no longer holds. Careful resonator design enables high output power to be extracted with unstable resonators without destroying the output couplers.     

High-power single-frequency tunable solid-state lasers

Experimental results are presented on the achievement of single-frequency tunable lasing in ruby, Nd-glass, and Nd:YAG lasers with electrooptic Q switching of the cavity by the injection of an external signal. An optimization of the parameters is carried out for lasers on neodymium ions in yttrium aluminum garnet, lanthanum beryllate, chromium-doped gadolinium scandium gallium garnet, and lanthanum hexaaluminate with passive Q switching of the cavity by means of lithium fluoride shutters containing F ₂ ⁻ color centers. High-power single-frequency generation of giant pulses is achieved, with the output wavelength tunable over the half-width of the gain lines of the active media. Zh. Tekh. Fiz. 68, 74–79 (October 1998)     

Beam parameters,mode structure and diffraction losses of slab lasers with unstable resonators

The properties of unstable resonators in on-axis and off-axis geometry were investigated both theoretically and experimentally. Diffraction loss, mode structure, beam quality and misalignment sensitivity were measured in single-shot operation with a gas-cooled Nd: YAG slab laser (4×12×100 mm³) and compared with theoretical results obtained by solving the Fresnel integral equation numerically. The excellent agreement allowed detailed resonator optimization. Furthermore, the resonator performance in high-power operation was investigated with two water-cooled Nd: YAG slab lasers (6×25×163 mm³ and 7×26×191 mm³) capable of 670 W of output power. Beam quality near the diffraction limit and a maximum output power of 475 W was achieved with an on-axis unstable resonator with variable-reflectivity mirror.     

High-power high-density-gas lasers

This paper presents a review of the work devoted to the creation and investigation of high-power pulsed uv, ir, and visible lasers pumped with an electron beam, a self-sustained discharge with uv preionization, and a discharge controlled and initiated by an electron beam. Attention is focused on exciplex (XeCl, KrF, KrCl) lasers, lasers operating by atomic transitions of xenon, nonchain HF lasers, and Penning neon plasma lasers. Institute of High Current Electronics, Siberian Branch of the Russian Academy of Sciences. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 8, pp. 37–42, August, 1999.     

Fiber lasers with hybrid birefringence resonators

We propose the combination of low- and high-birefringence fibers (Low-Bi and Hi-Bi, respectively) to form a hybrid birefringence resonator. The transmission characteristics as a function of different parameters for the fibers used within these hybrid resonators are obtained by means of Jones matrix analysis. This yields information on fiber laser features such as polarization mode-beating frequencies (PMB), which are used as readout for polarimetric sensors. We compare theoretical predictions with experimental results on the dependence of PMB frequencies as a function of wavelength and effective birefringence of the laser cavity. Applications of this hybrid fiber laser arrangement for polarimetric sensors and wavelength monitoring through PMB frequencies are also discussed. The results provide a simple way for optimizing fiber laser parameters and increase the sensitivity of PMB signals to wavelength variations.     

Positive-branch unstable resonators with thermal lens compensation

In order to compensate for thermal lensing in Nd : YAG rod active media, placed in unstable resonators with a super-Gaussian reflectivity profile of the output mirror, a deformable thin glass plate was used as the rear mirror. Unstable resonators with a magnification of M = 1.8 and with one and two Nd : YAG rods inside were investigated. By a proper variation of the radius of the thin glass plate, the magnification of the resonator was maintained constant by varying the refractive powers of the rods. For compensated resonators, the output energy of the laser working at 10 Hz repetition rate and pump energies up to 50 J per pulse was close to those obtained for a 1 Hz repetition rate.     

High-power monolithic unstable-resonator solid-state laser

We report the operation of a diode-pumped monolithic Q-switched unstable-resonator solid-state laser that generates 2.15-mJ, 2-ns pulses in a single transverse mode and a single longitudinal mode. We show that the unstable resonator is effective in suppressing the spatial and the temporal instability of the laser beam in a disk-shaped laser whose transverse dimension is comparable with or larger than its longitudinal dimension.     

Polarization manipulated solid-state lasers with crystalline-orientations

The polarization states of 〈111〉-cut Yb:YAG crystal microchip lasers were investigated by pumped with the elliptically polarized pump beam from fiber-coupled laser-diode. The manipulated polarized lasers were achieved in laser-diode pumped Yb:YAG microchip laser by controlling the crystalline-orientations in 〈111〉-growth Yb:YAG crystal. Generally elliptically polarized lasers were obtained in laser-diode pumped Yb:YAG microchip lasers. However, crystalline-orientation manipulated linearly polarized laser was obtained when six different sites with different crystalline orientations were set to parallel to the major axis direction of the elliptically polarized pump beam. Six different sites in Yb:YAG crystal were separated with 30° and 90°, which were responsible for the linearly polarized laser oscillations. Circularly polarized lasers were observed when a Yb:YAG crystal was aligned to a special position between two sites responsible for linearly polarized laser oscillation. Effects of the polarization states of pump source on the laser polarization states of Yb:YAG microchip lasers and polarization direction of different polarized lasers with respect to Yb:YAG crystal rotation was addressed.     

Ultrafast solid-state lasers

This article is intended to provide an introduction to ultrafast laser development for scientists new to the field and to provide a snapshot of the current state-of-the-art. In the first section, the main issues concerning ultrashort pulse generation are discussed and then the basic techniques of mode-locking are reviewed at a tutorial level. These include active mode-locking, passive mode-locking with real, resonant, saturable absorbers and passive mode-locking with the optical Ken effect. Emphasis is placed on practical ultrafast solid-state lasers for real-world applications.     

High-power tunable IR Raman lasers

Physical principles, new ways and means of creation, schemes, characteristics and features of efficient high-power tunable pulse Raman lasers, operating in the near and middle ir are reviewed. The paper includes: tunable dye and Nd lasers as pump sources; promising active media and their optimal excitation methods; optical systems for producing spatially homogeneous pumping; the physics of Raman oscillators and their practical schemes, efficient high pulse energy liquid N₂ and compressed H₂ Raman oscillators, covering several bands in the range between 1.4 and 9.2 μm; the physics and construction of efficient tunable Raman amplifiers-convertors, amplifying in the saturation regime of spontaneously scattered or beforehand produced and collimated external Stokes signals, obtained in the spectral range between 0.83 μm and 18 μm. Raman laser using a, so-called, broadband pump where the linewidth of pumping light is broader than the spontaneous scattering linewidth, are also discussed. Features of both amplification and oscillation regimes of such broadband pumped Raman lasers are reported, and conditions for the efficient frequency conversion are determined.     

High-power vertical-cavity surface-emitting lasers bonded with efficient packaging

<正>High-power vertical-cavity surface-emitting lasers(VCSELs) are processed using a wet thermal-selective oxidation technique.The VCSEL chips are packaged by employing three different bonding methods of silver solder,In-Sn solder,and metalized diamond heat spreader.After packaging,optical output power, wavelength shift,and thermal resistance of the devices are measured and compared in an experiment.The device packaged with a metalized diamond heat spreader shows the best operation characteristics among the three methods.The 200-μm-diameter device bonded with a metalized diamond heat spreader produces a continuous wave optical output power of 0.51 W and a corresponding power density of 1.6 kW/cm~2 at room temperature.The thermal resistance is as low as 10 K/W.The accelerated aging test is also carried out at high temperature under constant current mode.The device operates for more than 1000 h at 70℃,and the total degradation is only about 10%.     

Diode-pumped ultra-short-pulse solid-state lasers

Many materials are good candidates for diode-pumped ultra-short-pulse lasers: several transition-metal-ion-doped crystals can or could support extremely short fs pulses. This goal, so far, has only been reached by Cr³⁺:LiSAF, but there are good chances for other crystals like Cr⁴⁺:YAG having its bandwidth within the third communication window, and the high-yield Cr²⁺:ZnSe with its impressive bandwidth in the near IR. Rare-earth-ion-doped media deliver only sub-ps pulses but allow unprecedented and scalable high average powers, like a SESAM mode-locked Yb:YAG thin-disk laser described recently. In all ranges of pulse durations there are fascinating applications ready for widespread employment as soon as compact, reliable and moderately priced ultra-short-pulse systems will be available for the non-laser-skilled user. The highest impact in the near future is attributed to microstructuring of materials and processing of biological samples, including dental enamel, by ps and sub-ps pulses, and optical coherence tomography needing pulses in the 10-fs regime at very modest average powers. Received: 29 June 2000 / Published online: 6 December 2000     

Misalignment sensitivity of solid-state laser resonators with thermal lensing

An analysis of the resonator sensitivity to mirror misalignment in solid-state lasers is presented, considering the rod as a focusing lens with a limited aperture. For each mirror, a misalignment sensitivity factor S_i is defined in terms of resonator parameters. It is shown both theoretically and experimentally that, as a function of the pump power, two stability ranges labeled zone I and II exist, with markedly different S_i values; in particular, near one of the two boundaries of zone II, S_i rapidly diverges. The experiments, performed on a CW Nd:YAG laser, are in good agreement with the theoretical predictions.     

Microdrilling and micromachining with diode-pumped solid-state lasers

The trend of the ever-continuing miniaturization requires fast and flexible processing tools. Lasers are flexible tools which have proven their reliability in manufacturing of macrofeatures for many years already. However, to process small features the requirements of the laser source, e.g. in regard to the beam profile, are very high. Innovative laser sources which meet these requirements, such as diode-pumped solid-state lasers, and the progress in processing technology, have made microfeature processing commercially viable during recent years. Examples of industrial applications are laser-drilled micro-injection nozzles for highly efficient automobile engines or manufacturing of complex spinnerets for production of synthetic fibers. The unique advantages of laser-based techniques stem from their ability to produce high-aspect-ratio holes, while yielding small heat-affected zones with exceptional surface quality, roundness and taper tolerances. Additionally, the ability to drill blind holes and slots in very hard materials such as diamond, silicon, sapphire, ceramics and steel is of great interest for many applications in the microelectronics, semiconductor and automotive industries. This kind of high-quality, high-aspect-ratio micromachining requires high peak powers and short pulse durations. PACS 42.55.Xi; 42.62.Cf; 81.40.-z