Quasi-simultaneous ultraviolet and infrared emission from a plasma cathode TEA laser

Quasi-simultaneous laser action in the UV (0.337 μm) and the IR (10.6 μm) was observed from a pulsed laser with a sliding discharge plasma cathode. The laser operates at atmospheric pressure, with a gas mixture of CO₂/N₂/He, at a 0.26/0.50/4.0 lmin⁻¹ flow rate. Output energies of 30 mJ in the IR and 0.35 mJ in the UV were obtained, from a laser discharge volume of 38.0×1.0×2.8 cm³. The optimum gas mixtures have been determined and the temporal behavior of the discharge parameters, the performance characteristics of the laser and the beam spatial distributions were investigated.     

A compact 1.06/1.32/2.94 μm pulsed laser for dentistry

A three-wavelength pulsed laser for dental application is developed. The laser houses the Nd:YAG resonator (1.06/1.32 μm) for soft-tissue treatment and Er:YAG resonator (2.94 μm) for caries removal and fits and fissure treatment. Two heads share the cooling unit and two identical high-voltage power supply modules in order to achieve compactness. The Nd:YAG laser has 10 W at 1.06 μm and 7 W at 1.32 μm with a pulse duration of 100 μs. An Er:YAG laser of 2.94 μm has 3.5 W, 20 Hz and a pulse duration of 250 μs. The beams are delivered through fibers and the laser size is 75×55×32.5 cm.     

High power, long pulse, CH3I far infra-red laser

A high power, far infra-red laser, pumped by a long pulse high energy CO₂ laser, has been developed to produce 8 μs pulses at 447 μm. The influence of the molecular weight of the far infra-red gas on the absorption of the pump energy is discussed. The results show that the heavy molecules are most convenient for long pulse far infra-red lasers.     

Room temperature 2 μm Tm,Ho : YLF laser

We present the results obtained with a Tm,Ho : YLF crystal, grown in the new crystals growth facility realized in the Dipartimento di Fisica of the Università di Pisa. The 2 μm laser performance has been studied for three different pump sources, a Ti : Sapphire, a diode—tuned at 792.7 nm—and a Co : MgF₂ laser, tuned at 1.682 μm.     

He–SrCl2 vapor laser excited by Blumlein discharge circuit

An investigation of a He–SrCl₂ vapor laser excited by Blumlein discharge circuit is performed. Dependences of laser output power on the working parameters are obtained by experiment. The optimal operating parameters for lasing on several strontium atom and ion lines are found. The multi-line average output power of 1.32 W and the power specific of 12.46 mW/cm³ are achieved, of which more than 78.1% is concentrated at the 6.45 μm laser line.     

Novel long-pulse TE CO2 laser excited by pulser–sustainer discharge

A novel long-pulse TE CO₂ laser with UV-preionization is presented. With an active volume of 1.17 l and gas pressure of 30 kPa, the laser can discharge stably with low pulser energy and high sustainer energy. Various long-pulse discharges such as 12, 20 or 25 μs are demonstrated. At discharge pulse width of 23.9 μs, maximum output laser energy of 6.8 J is obtained at an efficiency of 9.0%.     

A comparison between characteristics of various laser-based denim fading processes

Our experiments show that the laser fading process has similar, even better results, in some cases, than the conventional technologies of indigo-dyed denim. Using the beams from Nd:YAG laser (1064 nm and its second harmonic 532 nm), CTH:YAG laser (2.09 μm), CO₂ laser (10.6 μm) and various laser beam parameters we found the optimum fluence and power density in order to obtain a similar fading appearance like the one obtained by conventional processes. The purpose of this work was to determine the effectiveness of laser-based technologies and to measure the wear characteristics of the processed textile like colorfastness, strength resistance, tearing strength, and dimensional changes.     

Q-switched NYAB laser end-pumped by a high-power diode-laser array

A diode-laser array end-pumped acousto-optically Q-switched NYAB laser operating at both 1.06 and 0.53 μm has been demonstrated. An average output power of 1.3 W at 1.06 μm at a pulse repetition frequency (PRF) of 60 kHz was obtained with an optical conversion efficiency of 18.1% and a slope efficiency of 21.3%. At the incident pump power of 6.1 W, the 1.06 μm shortest laser pulse was reached at PRF of 20 kHz with FWHM width measured to be 32 ns, yielding a largest pulse energy of 30 μJ, and a highest peak power of 938 W. The attainable maximum average green power was found to be 185 mW, with an optical conversion efficiency of 3%.     

Compact eye-safe laser sources based on OPOs with KTP or PPKTP crystals

We report on compact eye-safe nanosecond laser sources emitting in the 1.5 μm wavelength range based on non-critically phase-matched parametric interaction in optical parametric oscillators (OPOs) with KTP and periodically poled KTP (PPKTP) crystals, pumped by the fundamental frequency of Nd:YAG lasers. As much as 250 μJ signal pulse energy at 1.5 μm wavelength, 6.5 ns FWHM pulse-width, has been obtained in a PPKTP-OPO, extracavity pumped by a Nd:YAG microlaser oscillator–amplifier at 650 μJ pump pulse energy, 8 ns pulse-width. A single signal pulse of 2.7-mJ output energy at 1.57 μm wavelength, less than 5 ns pulse-width, was generated in a KTP-OPO, intracavity pumped by a passively Q-switched Nd:YAG laser.     

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.     

Thermal processes of a powder particle in coaxial laser cladding

This paper presents a numerical analysis of the heating, melting and evaporation processes of a single spherical powder particle when irradiated by a CO₂ laser beam in coaxial laser cladding. The power particle has a size ranging from 20 to 200 μm and the intensity of the laser has been varied from 500 to 3000 W. The laser energy, initial powder velocity and size have been shown to have important effects on the temperature profile of the powder stream. It has also been shown that high powder evaporation due to high power laser radiation may induce significant loss in the powder particle mass, to as much as 25% of the initial size at certain conditions in the simulation.     

Formation of microvias in epoxy-glass composites by laser ablation

Single CO₂ laser pulses, of 10.6μm wavelength, are used to form blind microvias (holes in electronic boards for through-plating conducting paths) in copper-clad epoxy-glass laminates. The microvia dimensions depend on pulse energy and duration, the thicknesses of the epoxy-glass laminate and copper cladding, and the distribution of glass within the epoxy-glass laminate. The useful range of laser parameters, especially pulse energy, is primarily determined by the ability to metallize subsequently the blind microvias. Several conclusions can be drawn from the data. The pulse enegy should be within ±20% of the optimum value in order to form vias with a cylindrical geometry. For 300 μm thick laminates, the thickness of the copper on the bottom should be 18 μm or more. A larger range of pulse energies could be used if the glass fibre density was more uniform and if subsequent copper metallization of the blind vias could be improved.     

Diode-laser pumped passively Q-switched green laser by intracavity frequency-doubling with periodically poled LiNbO3

A continuous-wave (CW) laser-diode (LD) pumped passively Q-switched intra-cavity frequency-doubling green laser is reported in this paper. We used 3% at Nd doped YVO₄ as gain medium, Cr⁴⁺:YAG as a saturable absorber for passively Q-switch and periodically poled LiNbO₃ (PPLN) as a frequency doubler. The output energy of the green laser is 1.96 μJ with the pulse-width of 15.6 ns. No green-noise problem exists in the green laser. Some theoretical results on the passive Q-switching and intra-cavity frequency-doubling are also discussed.     

Decay Time of 2.09 eV Luminescence of S2--Vacancy Centers and Their Optical and Thermal Stability in NaCl:S2 Crystals

An investigation was carried out on decay time of the 2.09 eV emission of S²–vacancy pair centers in NaCl crystals. When the crystal was excited by a pulsed 337 nm light from an N₂ laser, the 2.09 eV yellow luminescence principally decayed with the lifetime of 14.2 μs at low temperatures, and exhibited a weak thermal quenching with an activation energy of 51.3 meV above about 150 K. Such S^2--vacancy pair centers responsible for the 2.09 eV luminescence were thermally stable at room temperature, and not bleached even when exposed to ultraviolet lights below about 5 eV. Thus, the 2.09 eV emission center possibly can be used as a solid-state laser active center working at room temperature.     

High repetition rate mid-infrared laser source

An efficient, high-power mid-infrared laser source based on ZnGeP₂ (ZGP) optical parametric oscillator (OPO) is presented. Using a Q-switched Ho:YAG laser as the pump source a total output power of 10.6 W was obtained in the 3–5 μm band at 10 kHz and 8.5 W at 20 kHz. The Ho:YAG laser was pumped by two diode-pumped polarization coupled Tm:YLF lasers. Optical-to-optical efficiency achieved is >8.8% (laser-diode 792 nm to mid-IR 3–5 μm). With a commercial PtSi infrared camera (256×256 pixel focal plane array, 24 μm pitch) the pointing stability of Ho pump, signal and idler beam was measured to be better than 30 μrad. Whilst propagating the OPO beams over 100 m, little absorption for the idler beam was observed, resulting in a significant higher peak-to-peak value of ±22%, whereas the peak-to-peak stability of the signal pulses remained unchanged (±13%). To cite this article: M. Schellhorn et al., C. R. Physique 8 (2007).     

Multiple Beam Scanning Optics for Laser Printer: Application of Optical Fiber Array Method

We have developed laser printer optics using various kinds of multiple beam generation devices, such as a polarization prism, grating, diode laser array, and optical fiber array. Recently we successfully demonstrated laser-print experiments using five beams from an optical fiber array. In the array, fibers are arranged with a spacing of 0.15 mm and emit circular Gaussian beams that have a diameter of 5 μm and a wavelength of 635 nm. The wavelength of diode lasers is determined from sensitivity of the photoconductor drum of As₂Se₃ material. The arrangement error vertical to the array is mostly suppressed below 0.4 μm. In the optics, curve of scan lines and print position errors in the scan direction are suppressed to a negligible size due to minimization of the magnification variation in the sub-scan direction along the print width and achromatized design, respectively.This paper was originally presented at the 2nd International Conference on Optical Design and Fabrication, ODF2000 which was held on November 15-17, 2000 at the International Conference Center, Tokyo, Waseda University, Japan.     

Removal of the indigo color by laser beam–denim interaction

Our experiments show that the laser fading process removes efficiently indigo-dye from denim support. We use the beams from Nd : YAG laser (1064 nm and its second harmonic 532 nm) and CO₂ (10.6 μm) lasers. Different laser pulse parameters were used in order to obtain laser power density and fluency to start the ablation process. The purpose of this work is to determine the change of denim diffuse reflectivity spectra after laser irradiation with different wavelength and different power density. The change of diffuse reflectivity coefficient was up to 17% at 450 nm wavelength (from 8% reflectivity for unirradiated denim).     

A compact autocorrelator for the wavelength range between 4 and 10 μm

A compact autocorrelator suitable for the measurement of the optical pulse length of the infrared free electron laser (IR-FEL) at the S-DALINAC is described. It allows to investigate the energy transfer process from the electrons into the laser light within the undulator of the FEL. The autocorrelator utilizes the second harmonic generation (SHG) and it provides the possibility of a background-free measurement at wavelengths between 4 and 10 μm. Simulations for three different crystals used for SHG show that the largest efficiency for SHG and the best temporal resolution is achieved with a ZnGeP₂ crystal at a length of 2 mm. A test experiment at the free electron laser for infrared experiments confirmed the expected high efficiency of about 7.5% of SHG for the ZnGeP₂ crystal as well as the easy handling and fast adjustment of the system.     

A DFG spectrometer at 3 μm for high resolution molecular spectroscopy and trace gas detection

We report the realization and characterization of a spectrometer based on difference frequency generation using a periodically poled lithium niobate crystal. As signal and pump lasers we used a diode-pumped Nd–YAG laser (λ=1.064 μm) and an extended cavity semiconductor diode laser (λ=0.785 μm), respectively. The mid-infrared coherent radiation was produced at 3 μm with a maximum power of about 160 nW obtained with 340 mW of signal and only 3.4 mW of pump. That corresponds to an efficiency of 0.01%/Wcm, which is in good agreement with other data available in literature. The generated radiation around 3 μm has allowed us to study fundamental absorption bands of molecules of great atmospheric and physical interest such as water vapor and the hydroxyl free radical. In this work we report preliminary spectroscopic results concerning the ν₁ 5₄₁→6₅₂ H₂O line at 2.968 μm. In particular, for this line we provide the first experimental estimation of self-, N₂- and O₂-broadening coefficients.     

Surface treatment with linearly polarized laser beam at oblique incidence

An effective method for surface heat treatment with 10.6 μm linear polarized laser beam at oblique incidence is reported. A circular focused laser spot on the workpiece surface, simultaneously with 2.2–4 times increasing of the absorption are obtained in the 70–80° range of the incidence angle. The main element of the experimental setup is the astigmatic focusing head which focalize the laser beam into an elliptical spot of ellipticity >3 at normal incidence. At a proper incidence angle (obtained by the focusing head tilting) the focused laser spot on the work piece surface gets a circular form and p-state of polarization is achieved.We performed laser heat treatment (transformation hardening, surface remelting) of the uncoated surface, as well as the alloying and cladding processes by powder injection. An enhancement of the processing efficiency was obtained; in this way the investment and operation costs for surface treatment with CO₂ laser can be significantly reduced. Several technical advantages concerning the pollution of the focusing optical components, powder jet flowing and reflected radiation by the work piece surface are obtained.