High precision materials processing using a novel Q-switched CO2 laser

Holes with diameters of about 400 µm have been laser trepanned in Ti6Al4V and carbon fibre reinforced polymer (CFRP) thin sheets with a thickness of 0.5 mm. A commercial CO₂ laser (SM1500E, FEHA LaserTec, Germany) and a novel Q-switched CO₂ laser (µ-storm, IAI, Netherlands) were used as radiation sources. Optical microscopy, scanning electron microscopy and replicas of the processed holes were used to investigate the influence of the CO₂ laser pulse parameters (e.g. pulse energy, duration and peak power) on the processing quality. It was shown that melt formation and high temperature oxidation reactions of Ti6Al4V during thermal laser processing were reduced significantly by using short and high intense Q-switched CO₂ laser pulses. During trepanning of CFRP heat affected zones resulting from the extremely different thermal properties (melting and vaporisation temperature, heat conduction) of the reinforcing carbon fibres and the polymer matrix were reduced significantly by using the Q-switched CO₂ laser. The results demonstrate that Ti6Al4V and CFRP can be processed very precisely with CO₂ laser radiation and air as processing gas without melt formation and thermal damage.     

Long range anemometry using a CO2 laser

A CO₂ laser anemometer is described which gives a real-time, continuous, measure of one component of wind velocity. Results are presented of a series of trials in which the laser anemometer is compared with a conventional propeller anemometer at ranges up to 50 m from the laser. Very good agreement is observed between the outputs of the two devices.     

Studying the mechanisms of steel sheet perforation by the radiation of a continuous-wave fiber laser

Aspects of steel sheet perforation are studied experimentally. Calculations show that the mechanisms of thin sheet perforation change as the focal spot size is increased at a constant laser power. If the spot is small, the melt is removed and the film is disrupted by steel boiling in the spot center. With larger spots, the melt is removed by the force of gravity. The hole diameter grows along with the focal spot size and sheet thickness and is reduced upon an increase in laser power.     

Generation of ultrasound in materials using continuous-wave lasers

Generating and detecting ultrasound is a standard method of nondestructive evaluation of materials. Pulsed lasers are used to generate ultrasound remotely in situations that prohibit the use of contact transducers. The scanning rate is limited by the repetition rates of the pulsed lasers, ranging between 10 and 100 Hz for lasers with sufficient pulse widths and energies. Alternately, a high-power continuous-wave laser can be scanned across the surface, creating an ultrasonic wavefront. Since generation is continuous, the scanning rate can be as much as 4 orders of magnitude higher than with pulsed lasers. This paper introduces the concept, comparing the theoretical scanning speed with generation by pulsed laser.     

High-resolution spectroscopy of SO2 using a frequency-doubled,continuous-wave dye laser

The SO₂ molecule is of considerable interest in the context of atmospheric pollution, and in many laser monitoring techniques the ultraviolet absorption band at 300 nm is used to determine SO₂ concentrations in the atmosphere. Recent laboratory experiments with a resolution of 2 × 10^-3 nm showed that variations could occur in absorption cross-section measurements made with different laser bandwidths due to unresolved fine structure. We have investigated absorption spectra with a line width of 3 × 10^-6 nm, using a frequency-doubled continuous-wave dye laser, and have confirmed the existence of fine structure in the absorption even when collisionally broadened with an atmosphere of nitrogen. These measurements provide a data base from which valid absorption cross sections may be calculated for all monitoring laser bandwidths. We estimate the pressure broadening coefficient for nitrogen in this wavelength region as 83 ± 38 kHz Pa^-1 (11 ± 5 MHz torr^-1). The temperature dependence of the absorption cross-section was also investigated.     

Composition-spread thin films of pentacene and 6,13-pentacenequinone fabricated by using continuous-wave laser molecular beam epitaxy

Synthesis of continuous composition-spread (CCS) thin films is widely recognized in combinatorial material science as a powerful technique for rapidly investigating the properties of new functional materials. However, there are very few reports of CCS organic thin films due to the fact that the thermal evaporation method with Knudsen cells, which is commonly used to fabricate organic thin films in vacuum, does not offer the necessary level of deposition rate control as, for example, does pulsed laser deposition (PLD). We have successfully fabricated organic CCS thin films of pentacene and 6,13-pentacenequinone by continuous-wave laser molecular beam epitaxy (CWL-MBE), which we developed as a new fabrication method for organic thin films. The composition-spread films were characterized systematically by ultraviolet-visible spectroscopy, Fourier transform infrared spectroscopy, X-ray diffraction, atomic force microscopy, and two-probe conductivity measurements. The present work brings the advantages of high-throughput parallel synthesis and systematic characterization to the field of organic electronics, allowing for quick exploration and rapid optimization of organic functional materials and devices.     

Temperature effects on supercontinuum generation using a continuous-wave Raman fiber laser

We describe the effect of temperature variations on supercontinuum (SC) generation in optical fibers using a continuous-wave (CW) Raman fiber laser as a pump. We achieve supercontinuum generation by pumping only ∼2 W of power into a 7 km-long nonzero dispersion-shifted fiber (NZDSF) in the region of small anomalous dispersion. In these conditions, the supercontinuum builds up basically on modulational instability and Raman. At room temperature, the supercontinuum covers effectively the S, C and L transmission bands defined by the International Telecommunication Union (ITU). Temperature tuning of the fiber environment provides a means of tuning the fiber dispersion, and thus a means of changing the width and shape of the supercontinuum spectrum. We demonstrate a 27% increase in the 10-dB SC width. We believe that the application of this new tuning mechanism to other experimental configurations using pulsed sources might be used to produce extremely broad supercontinuums.     

Pyroelectric detection of a CO2 laser beam using organic copolymers

Pyroelectric detection of a CO₂ laser beam has been investigated by using organic copolymers such as VDF/TrFE- and VDCN/VAc copolymers, and compared with that of PVDF polymer. The voltage responsitiviesR _v are 40 mV/W for VDF/TrFE and 2 mV/W for VDCN/VAc at room temperature and at a chopping frequency of 200 Hz. (For comparison, the value of PVDF is 20 mV/W.) From the frequency dependence of the detected output, the electric time constant _E is evaluated to be about 6.4 ms and 2.6 ms for the former and latter copolymers with the detection area 3×3 mm², respectively. Some theoretical discussion is also given of the responsivity, frequency dependence and temperature dependence obtained.     

Further study of continuous-wave CO flame chemical laser of the CS2/O2/N2O type

This report describes an experimental examination of the output characteristics of the continuous-wave (cw) carbon monoxide flame chemical laser (FCL) of the CS₂/O₂/N₂O type in case of small CS₂/O₂ reactants ratios (tipically CS₂/O₂≦1/10). A linear burner which gives a homogeneous and stable flame was used during the experimental study. The measurements of temperature distribution in CS₂/O₂ as well as CS₂/O₂/N₂O flames show maximum temperatures of 1040 and 890 K, respectively. The addition of nitrous oxide (N₂O) leads to dramatically enhanced output laser power caused primarily by V?V transfer processes. A chemical efficiency, based on the reaction O+CS→CO^*+S, of 3% was achieved. The spectral composition of the CO FCL of the CS₂/O₂/N₂O type shows lasing in the region from 5.130 to 5.586 μm. Experimental results were obtained with a nondispersive optical cavity.     

Oxygen isotope ratio measurements in CO(2) by means of a continuous-wave quantum cascade laser at 4.3 mum

A mid-infrared laser spectrometer was developed for simultaneous high-precision (18)O/(16)O and (17)O/(16)O isotope ratio measurements in carbon dioxide. A continuous-wave, liquid-nitrogen cooled, distributed feedback quantum cascade laser, working at a wavelength of 4.3 microm, was used to probe (12)C(16)O(2), (16)O(12)C(18)O, and (16)O(12)C(17)O lines at ~2311.8 cm(-1). High sensitivity was achieved by means of wavelength modulation spectroscopy with second-harmonic detection. The experimental reproducibility in the short and long terms was deeply investigated through the accurate analysis of a large number of spectra. In particular, we found a short term precision of 0.5 per thousand and 0.6 per thousand, respectively, for (18)O/(16)O and (17)O/(16)O isotope ratios. The occurrence of systematic deviations is also discussed.     

管状预电离可调谐TEA CO2激光器.

研制了一种新型的预电离结构--管状预电离器,并将其应用于可调谐TEA CO2激光器.利用光栅选线方案,采用光栅谐振腔,实现了激光的调谐输出.在输出耦合率为50%、气压为40 kPa的条件下,10P(20),10R(20),9P(20),9R(20)四条谱线获得的最高电光转换效率,分别为9.5%,9.7%,9.8%,9....     

Structural phase modification of glass-ceramic materials under CO2 laser irradiation

Reversibility of the structural phase modification of glass-ceramics (photosensitive and nonphotosensitive) under CO₂-laser irradiation has been experimentally demonstrated. It is shown that CO₂-laser irradiation leads to glass crystallization and subsequent reverse amorphization of the glass-ceramics FS-1 and ST-50-1. Upon laser heating, the rate of such structural modifications is two to three orders of magnitude higher than upon stationary furnace heating. The technology of laser structural modification of glass-ceramics is promising for developing and manufacturing new optical and other types of elements and microstructures.     

Gain saturation in a continuous-wave argon laser

Results are given for the 0.488m line, which agree well with theoretical predictions for uniform saturation. An approximate value for the saturation parameter is derived.     

Fourth-harmonic generation of a continuous-wave CO(2) laser by use of an AgGaSe(2)/ZnGeP(2) doubly resonant device

We report a doubly resonant continuous-wave CO(2) laser frequency-quadrupling device that generates 200nW of 2.55-mum (4?) and as much as 2mW of 5.1-mum (2?) radiation out of 1.7-W fundamental radiation at 10.2 mum (?). The quadrupling process results from two resonant cascading second-harmonic generations by use of a walk-off-compensated twin AgGaSe(2) device (??2?) and a ZnGeP(2)nonlinear crystal (2??4?).     

A tunable,frequency-doubled,continuous-wave dye laser using ADA

A tunable, continuous-wave, frequency-doubled, rhodamine 6G dye laser has been developed using an ADA crystal placed in an astigmatic and coma compensated cavity. Generated UV powers of the order of 30mW cw in a single direction in gaussian form over the range 292–302 nm have been obtained by temperature phase matching, and with a 4.5 W pump. Power output is affected by thermal phase mismatching, and is ultimately limited by thermal lensing. Two scanning systems have been developed; a broadband arrangement of linewidth 0.02 nm continuously tunable over a range of 2 nm, and a narrowband system of linewidth 0.002 nm continuously tunable over a range of 1 nm. The laser has been used to detect the Rydberg states of Rb up to a principal quantum of n = 74.     

An acousto-optic modulator for a CO2 laser rangefinder using heterodyne detection

The ability to superimpose arbitrary modulation waveforms on a CW laser beam makes the acoustooptic modulator suitable for an important task: to apply modern microwave radar electronic signalprocessing and signal-generation techniques to heterodyne CO₂ laser radar systems. The fundamental constraints on modulator design are first presented graphically in a novel treatment. The fabrication of 50–70 MHz germanium-lithium niobate modulators for a CO₂ laser radar is then described. Experimental measurements of efficiency (about 4% per electrical watt transducer input power) and rise time ( 40 ns) are finally presented.     

Intraresonator method for investigating the kinetics of stimulated absorption in crystals using continuous-wave CO2 lasers

Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 56, No. 3, pp. 399–403, March, 1992.     

Investigation of the spectral content of a cw CO laser output using a high-resolution scanning Fabry-Perot interferometer

The use of a scanning Fabry-Perot interferometer of variable length (variable resolution) for investigating the output of a cw CO laser is reported. Under experimental conditions required to achieve maximum power it was found that the laser output consisted of two or more simultaneously occuring transitions due to the overlapping nature of the vibration- rotation bands. The frequency differences between these transitions were measured to an accuracy of 0.01 cm^-1. Operation of the CO laser on a single vibration-rotation transition was obtained by controlling the laser gain with the experimental variables of discharge pressure, gas temperature, and optical alignment. An alternative approach of obtaining monochromatic radiation, by using a Fabry-Perot interferometer as a frequency selective filter external to the CO laser, is reported.