Hard tissue ablation with a free running Er:YAG and a Q-switched CO2 laser: a comparative study

The Er:YAG and the CO₂ laser are competitors in the field of hard tissue ablation. The use of Er:YAG lasers (2.94 μm, pulse length _L of 100 to 200 μs) show smaller areas of thermal defects then ‘‘superpulsed’’ CO₂ lasers with pulse lengths of approximately 100 μs. Only the development of a Q-switched CO₂ laser (9.6 μm, τ_L=250 ns) allowed for similar results. In this paper new results for the Er:YAG and the Q-switched CO₂ laser under the influence of water spray will be presented. Several parameters are of special interest for these investigations: the specific ablation energy, which shows a minimum for the CO₂ laser at an energy density of 9 J/cm ² and a broad shallow minimum in the range of 10 to 70 J/cm² for the Er:YAG laser, and comparison of the cut-shape and depth. Surface effects and cutting velocity are discussed based on SEM pictures. Received: 19 July 2000 / Revised version: 1 November 2000 / Published online: 30 November 2000     

Efficient high-power Ho:YAG laser directly in-band pumped by a GaSb-based laser diode stack at 1.9 μm

An efficient high-power Ho:YAG laser directly in-band pumped by a recently developed GaSb-based laser diode stack at 1.9 μm is demonstrated. At room temperature a maximum continuous wave output power of 55 W at 2.122 μm and a slope efficiency of 62% with respect to the incident pump power were achieved. For narrow linewidth laser operation a volume Bragg grating was used as output coupler. In wavelength stabilized operation a maximum output power of 18 W at 2.096 μm and a slope efficiency of 30% were obtained. In this case the linewidth is reduced from 1.2 nm to below 0.1 nm. Also spectroscopic properties of Ho:YAG crystals at room temperature are presented.     

Application of mid-infrared laser radiation for lithotripsy

The perforation effects of Er:YAG (2940 nm) and Ho:YAG (2100 nm) lasers radiation on human urinary stones model made from compressed plaster and real human samples were compared in vitro. For mid-infrared laser radiation delivery the special COP/Ag hollow glass waveguides were used. From the interaction experiments the perforation rates were derived and compared for both lasers. From the results it can be evaluated that Er:YAG laser radiation is favourable in comparison with Ho:YAG laser in case of artificial samples perforation efficiency.     

Laser radiation tunable within the range of 4.35–5.45 <Emphasis Type="Italic">μ</Emphasis>m in a ZnTe crystal doped with Fe<Superscript>2+</Superscript> ions

We realized laser generation on a Fe²⁺:ZnTe crystal for first time. The crystal was pumped at room temperature by 40 ns pulses of an Er:YAG laser operating at a wavelength of 2.94 μm in the Q-switching mode. The output energy of the Fe²⁺:ZnTe laser was 0.18 mJ at a slope efficiency of 2.4% with respect to absorbed pumping energy. We achieved tuning of the Fe²⁺:ZnTe laser generation wavelength within the range of 4.35–5.45 μm using a prism-dispersion cavity.     

8.30 μm singly resonant ZnGeP2 optical parametric oscillators pumped by a Tm,Ho:GdVO4 laser

A single resonator 8.30 μm ZnGeP₂ (ZGP) optical parametric oscillators (OPO) was reported in the paper. The OPO was pumped by a 10.2-W Tm,Ho:GdVO₄ laser at 8 kHz in a Q-switch mode, a 170-mW idler was obtained at 8.30 μm, and the output power of the idler and signal wave was 1.0 W, corresponding to an optical-optical conversion efficiency of 10.3% and a slope efficiency of 20.9%. Tm,Ho:GdVO₄ laser was pumped by a 30-W fiber-coupled laser diode (LD) at the center wavelength of 801 nm. The output wavelength of Tm,Ho:GdVO₄ laser was at 2.05 μm, and the energy per pulse of 1.28 mJ in 18 ns was achieved at 8 kHz with the peak power of 71.1 kW.     

Diode-pumped actively Q-switched Tm:YAG ring laser operation at room temperature

2-μm lasers with high pulse energy and long pulse width of hundreds of nanoseconds are needed urgently in the accurate wind velocity lidar systems. This paper presents the acoustic-optical Q-switched Tm:YAG laser performance in a pulsed-laser-diode end-pumping figure-eight ring resonator structure. Pulse energy and pulse width are investigated with the increasing of the incident pump energy at different repetition rate operation. Maximum energy of 4.6 mJ with the pulse width of 179.2 ns and 3.57 mJ with pulse width of 184.4 ns are obtained at the repetition rate of 20 and 100 Hz, respectively. Under free-running and Q-switched operation, the peak output wavelength is 2.014 μm at all time, and the beam quality factors are lower than 2 times diffraction-limited measured by a knife-edge traveling method.     

Direct laser writing of near-IR step-index buried channel waveguides in rare earth doped YAG

A new (to our knowledge) ultrashort laser pulse irradiation regime that allows us to directly modify and increase the refractive index of rare earth doped YAG polycrystalline ceramics has been identified. Single-mode buried channel waveguides in both Ho:YAG and Er:YAG ceramics at the near-IR wavelengths of 1.55?μm and 1.95?μm are demonstrated by fabricating positive square step-index cores. Minimum propagation losses of 1.5?dB?cm(-1) at a 1.51?μm wavelength have been preliminarily obtained. Confocal microluminescence mapping reveals that the increased refractive index regions retain the near-IR spectral properties of Er3+ ions in the YAG crystalline matrix.     

Optical systems for high-power laser applications: principles and design aspects

Starting from the optical properties of laser beams, the requirements of optical systems for manipulating laser radiation in industrial applications are derived. The relevant parameters, relations to the diffraction limit and the state-of-the-art design techniques are discussed. The three important types of lasers for use in industrial materials processing operate at wavelengths ranging from the infrared (10.6 m, CO₂ laser; 1.06 m, Nd:YAG) to the ultraviolet region (excimer lasers). Each wavelength range is associated with specific design challenges. The scarcity of suitable refractive materials for the 10 m wavelength range and the ultraviolet below 300 nm is a major constraint. Reflective systems are used widely at the longer wavelength, but some designs suffer from coma. The 1.06 m radiation from the Nd:YAG laser can make use of many well-developed optical means for handling visible light. Energy transport by optical fibres is commonly used. Optical systems for excimer laser applications are specific in that they image a mask onto a workpiece, and use the high photon energy and the high definition possible with the short wavelength for precision micro-machining.     

Cr:Tm:Ho:YAG (2.1 μm) and Nd:YAG (1.444 μm) pulsed-laser lithotripsy of bile duct stones

The Nd:YAG (1.444 m) and Cr:Tm:Ho:YAG (2.1 m) free-running laser systems of the output energy of 300 mJ per pulse and repetition rate 1 Hz have been developed and used for bile duct stones fragmentation study in vitro. A total of 67 human bile duct stones of known sizes, collected from surgical sources were used in the experiments. Insensitivity of the stones fragmentation to the type of the laser used, and insensitivity of the fragmentation efficiency to the type of stone, was observed. No pathological changes of the tissue were observed for non-human soft tissue laser irradiation (in vitro) by 1, 2, and 5 pulses of the Cr:Th:Ho:YAG radiation of the fluency of 1.6 J/cm². The lasers are found to be good candidates for laser lithotripsy.     

Pulsed infrared radiation transmission through chalcogenide glass fibers

Two different kinds of chalcogenide glass IR fibers were evaluated relative to transmission of pulsed IR radiation produced by several laser sources in the wavelength range from 1 to 10 μm. Fibers composed either from As-Se-Te or from As₂S₃ glass, of 250, 500, 750 and 1000 μm and 250, 750 and 1000 μm core diameters were studied, respectively. Attenuation measurements were obtained as a function of the laser energy input and as a function of curvature, wherever this was possible. The output beam quality was also studied using a beam profiler. The lasers used were a Q-switched Nd:YAG laser, emitting at 1.06 μm, a free-running or Q-switched Er:YAG laser emitting at 2.94 μm and a tunable pulsed CO₂ laser emitting in the range of 9.3-10.6 μm. The fibers exhibited better behavior when tested with the Er:YAG laser and they were found fragile in pulsed radiation from the Nd:YAG and the CO₂ laser. The output beam profiles generally showed a central multi-spiking energy distribution.     

Research of Tm (5.5 at %), Ho (0.55 at %):GdVO<Subscript>4</Subscript> laser pumped by diode laser at 800 nm

In this paper, we report a Tm (5.5 at %), Ho (0.55 at %):GdVO₄ laser pumped by diode laser at 800 nm. To our best knowledge, it is the first time that the use of Tm (5.5 at %), Ho (0.55 at %):GdVO₄ crystal among the similar experiments. We observed the influences of LD working temperature i.e. pump wavelength to 2 μm laser conversion efficiency. In the conditions of the continuous wave and 10 kHz acousto-optic Q-switch, high efficiency output of 2.05 μm laser was obtained. With the maximum pump power of 34.6, 13.9, and 13.6 W at 2.05 μm laser output was achieved respectively. Single laser pulse width was 25.6 ns in 10 kHz acousto-optic Q-switched condition.     

Sub-nanosecond passively Q-switched Yb:YAG/Cr4+:YAG sandwiched microchip laser

We report on laser-diode pumped low-threshold, and compact passively Q-switched Yb:YAG microchip lasers, with Cr⁴⁺:YAG crystals as the saturable absorbers. The laser threshold at the fundamental wavelength of 1.03 μm is as low as 0.25 W, and the slope efficiency is as high as 36.8%, and the optical-to-optical efficiency is as high as 27% for the 95% initial transmission of the Cr⁴⁺:YAG crystal. A pulse width of 1.35 ns and peak power of over 8.2 kW was obtained. Using a 5 mm thick KTP crystal as the second-harmonic generation medium, 514.7 nm green light of 155 mW power was generated. The pulse duration of 480 ps was generated at 1.03 μm by using 85% of the initial transmission of the Cr⁴⁺:YAG saturable absorber. Stable single-longitudinal-mode oscillation and wide-separated multi-longitudinal-mode oscillation due to the etalon effect of the Cr⁴⁺:YAG thin plate was achieved at different pump power levels. PACS 42.55.Sa; 42.55.Xi; 42.60.Gd     

Efficient room-temperature operation of Cr3+-sensitized,flashlamp-pumped, 2µm lasers

Utilizing the results of Cr³⁺ → Tm³⁺ transfer efficiency studies, we have demonstrated that yttrium aluminium garnet (YAG) is the preferred host for room-temperature, flashlamp-pumped solid-state lasers operating in the 2.0 µm spectral range. We report data on two different sensitizer-activator combinations in YAG and yttrium scandium gallium garnet (YSGG) laser materials: one is doped with Cr:Tm:Ho and operates on the Ho³⁺⁵I₇ →⁵I₈ transition at 2.097 µm; the other is doped only with Cr:Tm, which lases on the Tm³⁺³F₄ →³H₆ transition at 2.014 µm. We have achieved a slope efficiency of 5.1% with the Cr:Tm:Ho:YAG laser, which is the highest slope efficiency yet reported for a room-temperature, flashlamp-pumped, 2 µm solid-state laser. We have measured thresholds as low as 38 J and output energies >1.5 J for that system. We also report the first room-temperature operation of an efficient flashlamp-pumped Cr:Tm:YAG laser at 2.014 µm. Thresholds as low as 43 J, output energies exceeding 2 J, and slope efficiencies as high as 4.5% have been achieved. This is an order of magnitude higher than the efficiency previously reported for a 2.01 µm Cr:Tm:YAG laser operated at cryogenic temperatures. These two efficient 2 µm laser systems (Cr:Tm:Ho:YAG and Cr:Tm:YAG) are discussed in terms of their potential for Q-switched operation.     

Experimental investigation of pulse diodes side-pumped 2 μm Tm:YAG lasers

The free running and Q-switched operation of 2 μm Tm:YAG lasers side-pumped by pulse laser diodes were reported. In the free running mode the maximum output energies were 102.5 mJ at 1 Hz and 94.6 mJ at 10 Hz, respectively. With an acousto-optic modulator in the laser resonator, 21 mJ 2 μm Q-switched pulse was obtained, with a pulse width of about 330 ns. The dependences of the output energy and the efficiency on the laser resonator parameters were investigated.     

A comparative study on diode-pumped continuous wave Tm:Ho:YVO<Subscript>4</Subscript> and Tm:Ho:GdVO<Subscript>4</Subscript> lasers

In this paper, we presented experimental results concerning on the laser characteristics of two microchip lasers emitting in the 2 μm range, Tm:Ho:YVO₄ microchip laser and Tm:Ho:GdVO₄ microchip laser. At a heat sink temperature of 283 K, the maximum output power of Tm:Ho:YVO₄ laser and Tm:Ho:GdVO₄ laser is 47 and 34 mW under absorbed pump power of 912 mW, respectively. High efficiency can be achieved for both lasers at room temperature. Nevertheless, compared with Tm:Ho:GdVO₄ laser, Tm:Ho:YVO₄ laser can operate on single frequency with high power easily. At the heat sink temperature of 288 K, as much as 16.5 mW of 2052.3 nm single-longitudinal-mode (SLM) laser was achieved for Tm:Ho:YVO₄ laser. Under the same condition, only 8 mW of 2048.5 nm SLM laser was achieved for Tm:Ho:GdVO₄ laser.     

Continuous wave operation of singly-doped Ho:LSO laser at room temperature

We present the room-temperature continuous-wave Ho:LSO laser single-pass-end-pumped by a diode-pumped Tm:YLF laser at 1.91 μm in this paper. Under different output couplers of 2.4, 5.0, and 14.0%, the laser output power and output spectrum of Ho:LSO laser operating at room temperature are investigated. The output wavelength of Ho:LSO laser was centered at 2106.5 nm with linewidth (FWHM) of about 3.2 nm. With T = 5.0%, the maximum output power of 2.4 W was achieved under the absorbed pump power of 11.1 W, corresponding to a slope efficiency of 38.0%.     

In-band pumped Ho:YAP laser by Tm-Doped fiber laser at 1936 and 1948 nm,respectively

We present for the first time a highly efficient Ho:YAP laser at 2117.9 nm, which is double-end inband pumped by two all-fiber Tm-doped fiber lasers at 1936 and 1948 nm. Using a single 50 mm long Ho:YAP rod in a simple L-shaped resonator geometry, a maximum laser output power of 10.1 W and a slope efficiency of 43.6% with respect to the incident pump power are acquired. The Ho:YAP crystals work under room temperature 24°C, and without any active thermal management. This experimental results verify the Ho:YAP crystals can be pumped by the versatile laser sources in the 1.9 μm regions.     

Estimation of required parameters for detection of small smoke plumes by lidar at 1.54 μm

Parameters of eyesafe lidar at 1.54 μm for detection of small plumes of smoke from burning wood or oil have been evaluated. It was assumed that a diode-pumped solid-state Er:glass laser at 1.54 μm or a Nd:YAG laser with a Raman cell or optical-parametric oscillator is used as a light source and that detection of backscattered light is performed with an avalanche photodiode. Ash and soot particle size distributions were taken from experiments. A backscattering coefficient at 1.54 μm for various source of smoke was estimated. In computing the laser energy, range between lidar and smoke, receiver optics diameter, fuel mass burned in unit time, fire source radius, laser pulse duration and visibility were varied. Results of the computations enabled estimation of the required laser energy, which ranges from 0.05 to 1400 mJ depending on the parameters. Received: 5 January 2000 / Revised version: 3 March 2000 / Published online: 11 May 2000     

RIR-MAPLE deposition of conjugated polymers for application to optoelectronic devices

Resonant-infrared matrix-assisted pulsed laser evaporation (RIR-MAPLE) is a promising deposition technology for the fabrication of conjugated polymer-based optoelectronic devices for two primary reasons: (i) the ability to control film morphology, and (ii) the ability to deposit multi-layered heterostructures. This article reviews a variation of RIR-MAPLE that uses emulsified targets of organic solvents and water such that the incident laser wavelength (Er:YAG at 2.9 μm) is resonant with hydroxyl (O–H) bonds in the host matrix, which are absent from the guest material. The novelty of the approach lies in the fact that while most polymers of interest and many compatible solvents do not resonantly absorb the laser energy at 2.9 μm, the emulsion with water enables high-quality, thin-film deposition with minimal photochemical and structural degradation for almost any polymer of interest. In addition, the advantages of emulsion-based RIR-MAPLE for conjugated polymer-based optoelectronic devices are demonstrated by two important studies. First, conjugated polymer films deposited by RIR-MAPLE are shown to have higher hole drift mobilities than films deposited using traditional drop-casting and spin-casting techniques. Second, the unique capability of RIR-MAPLE to enable conjugated polymer-based optical heterostructures is demonstrated by the fabrication and characterization of a multi-layer, polymer distributed Bragg reflector.     

Low-threshold gas lasers pumped by plasma-cathode accelerators

The lasing on the electronic transitions of xenon and neon is studied. It is demonstrated that plasma-cathode accelerators serve as effective sources for the pumping of low-threshold lasers (W < 100 W/cm³). The laser energy in xenon at the wavelength λ = 1.73 μm is 5 J at an efficiency of 2%, and the laser energy in neon at the wavelengths λ = 585.3 nm is 0.5 J at an efficiency of 0.3%. The repetitively pulsed mode of the xenon and neon lasers carried out at a repetition rate of 50 Hz. The radiation energy of a wide-aperture laser with an active volume of 600 l is 100 (0) J for a wavelength of 1.73 (2.03) μm at an efficiency of 2% (1%). Original Text ? Astro, Ltd., 2006.