TEA Laser Research Articles

A new basic structure suitable for a fully integrated all-fiber-optic stimulated emission dye source

In the present work, our research is focused on an innovative compact all-fiber-optic structure suitable for the development of fully integrated dye lasers. The structure is based on a standard fiber-optic glass ferrule with two parallel openings along its length with diameters of 125 μm. A Fabry-Perot cavity is formed in one of the openings using two fused silica optical fibers with flat end facets. An angle-polished optical fiber with a reflective metal coating is placed in the second opening through which the active medium is pumped transversely. The active medium used is the Rhodamine 6G dye dissolved in glycerine, which is pumped by the 337.1-nm wavelength laser pulses of a nitrogen TEA laser. The ferrule-based design allows for a simplified set-up procedure and the integration of the pumping system to the basic structure of the laser, thus making it very compact. The design of the light source presented allows its future use in applications, such as lab-on-a-fiber, lab-on-a-chip and total analysis micro systems.

Maximizing the efficiency of a compact helium-free TEA CO2 laser: Experimental results and theoretical simulation

The design, development and operational characteristics of a compact corona pre-ionized helium-free TEA CO2 laser is discussed. Remarkably high efficiency of about 19% was obtained in this laser, which is attributed to the optimum concentration of CO2 and N2 gas, reduction in energy dissipation in the pre-ionization loop and the switch, minimizing the diffraction losses and finally optimization of the output coupler reflectivity. The helium-free TEA CO2 laser has also been analysed using a comprehensive theoretical model, developed based on the Boltzmann transport equations and the discharge excitation circuit equations. The voltage and current waveforms of the pulsed discharge were simulated and used as input to the laser rate equations to estimate the laser pulse energies and the pulse shapes. The theoretical estimations of the laser pulse energy agree fairly well with the experimental results. The accuracy of our theoretical model becomes evident from the numerically evaluated laser pulse shapes, which show remarkable resemblance with the experimentally measured pulse shapes. A detailed comparison with the helium-rich case is included to highlight the key aspects of a suitably designed helium-free TEA laser.

Magnetic and Desorption Cryogenic Calorimeters as Supersensitive Detectors of Far IR Radiation

In this work, we estimate the potential of a cryogenic far IR radiation detector for registering the energy release by the amount of a substance desorbed upon its exposure to far IR quanta. The temperature invariability of the system at the first-order phase transition excludes the diffusion character of heat transfer processes, which contributes to the detector’s speed of operation and, according to our estimates, enables its use in pulsed location systems based on a CO2 TEA laser. As an example of another cryogenic detector, we consider an antiferromagnetic, where the speed of operation is provided by the resonance transfer of far IR quantum energy to the spin system, the sublevels of which are split by a strong (∼1,000 T) exchange field. The magnetic response arising in this case is registered by a quantum magnetometer based on the Josephson effect.

Repetitively pulsed TEA laser and its application for second harmonic generation in crystal

Experimental results are presented on the development of a radiation source emitting at a wavelength of with a pulse energy up to and an average power up to several watts in short pulse trains. A TEA laser and a nonlinear converter based on a crystal, which are specially designed for these experiments, are described. The main limitations of nonlinear conversion and possible ways to overcome these limitations are considered.

Improved repetition rate mixed isotope CO₂ TEA laser.

A compact CO2 TEA laser has been developed for remote chemical detection that operates at a repetition rate of 250 Hz. It emits 700 mJ/pulse at 10.6 μm in a multimode beam with the (12)C(16)O2 isotope. With mixed (12)C(16)O2 plus (13)C(16)O2 isotopes it emits multiple lines in both isotope manifolds to improve detection of a broad range of chemicals. In particular, output pulse energies are 110 mJ/pulse at 9.77 μm, 250 mJ/pulse at 10 μm, and 550 mJ/pulse at 11.15 μm, useful for detection of the chemical agents Sarin, Tabun, and VX. Related work shows capability for long term sealed operation with a catalyst and an agile tuner at a wavelength shift rate of 200 Hz.

Relation Between Discharge Length and Laser Pulse Characteristics in Longitudinally Excited CO2 Laser

A longitudinally excited CO2 laser pumped by a fast discharge emits a short laser pulse, similarly to TEA and Q-switched CO2 lasers. We investigated the relation between the discharge length and the laser pulse characteristics to develop a longitudinally excited CO2 laser producing a high spike laser pulse. We examined discharge lengths of 30, 45, and 60 cm, using the same mirrors and the same excitation circuit with the same input energy. A longer discharge length increased the discharge volume and improved the laser output energy. However, the longer discharge length caused a long discharge formation time (a slow fall time of the discharge voltage) due to the higher discharge impedance, which resulted in a long laser pulse tail. Therefore, the longitudinally excited CO2 laser had optimum conditions for obtaining a high spike laser pulse effectively.

Fast Discharge Circuit for Longitudinally Excited CO2 Laser

In a longitudinally excited CO2 laser with a short laser pulse, similarly to TEA and Q-switched CO2 lasers, a fast discharge is very important. We investigated the use of a fast discharge circuit to obtain a high spike laser pulse in a longitudinally excited CO2 laser. We compared a traditional capacitor-transfer circuit having a buffer capacitance of 700 pF with our direct-drive circuit in which the buffer capacitance is removed. The direct-drive circuit produced a fast discharge and a high spike laser pulse. We also investigated the effect of a resistance connected in parallel with the discharge tube to eliminate low discharge current after the main discharge. A low resistance of 1 kΩ or less acted as a shunt resistance. The shunt resistance was effective in decreasing the energy of the laser pulse tail at high gas pressure.

Optimisation of a paint coating ablation process by CO 2 TEA laser: Thermal field modelling and real-time monitoring of the process

The ablation of coatings (paint, varnish, oxides, etc.) using a pulsed laser beam is a process that has a number of major benefits compared with conventional cleaning techniques (mechanical and chemical), the main advantage being the possibility of removing the surface layer without any risk of damaging the substrate. Another benefit, and certainly not the least, is the non-use of toxic solvents or chemical products that are difficult to eliminate and, in any case, will be banned from use in the near future. However, it must be stressed that, notwithstanding the above benefits, laser ablation of painted surfaces can only give good quality results if the process is properly controlled. The procedure discussed in this paper has two aims: the first involves establishing a thermal model of the interaction, applied to the ablation of paint from metal surfaces by infra-red laser. The second involves proposing an optimised paint removal process validated by experimental measurements. This second objective will be based on an analysis method of the acoustic signal transmitted by the ablation plasma beam.

SiF 4 IR Photodissociation: Gas phase reactions of SiF 3 with CH 4

The infrared multiphoton dissociation (IRMPD) of SiF 4 in the presence of CH 4 has been studied using a tunable CO 2 TEA laser. The siliconated reaction products have been identified. A kinetic scheme has been proposed to explain the experimental results. The reaction rate constant of the trifluorosilyl radical, SiF 3, with CH 4 has been obtained from the numerical solution of the differential equation system associated to the kinetic mechanism proposed as well as from non-linear regression methods. It has been additionally found that this reaction occurs through two channels. The relative importance of each and their reaction rate constants have been determined as well.

Detection of small N 2O concentrations using a frequency doubled 12C 18O 2 laser

A reliable procedure for remote high-accuracy laser detection of N 2O as one of the principal destroyers of the protective ozone layer of the Earth has been developed. The procedure is based on using a CO 2-laser system emitting efficiently in the ∼4.5 μm range. In this case lasing from isotopic modification 12C 18O 2 of carbon dioxide with its subsequent frequency doubling by a nonlinear crystal is used. With the object of reducing the price the composition of the active medium (both for TEA laser and low-pressure longitudinal-discharge-excitation laser) has been optimized. New high-efficiency intracavity frequency doubling schemes based on nonlinear AgGaSe 2 crystals have been developed for CO 2-lasers of both types. Low concentrations of N 2O and concentrations of the principal background gases CO and H 2O have been measured under real atmosphere conditions with the aid of the lidar complex built around these lasers.

Infrared multiphoton dissociation of SiF 4: gas phase reactions of SiF 3 with F and H 2

The infrared multiphoton dissociation (IRMPD) of pure SiF 4 and in mixtures with different gases was studied using a tunable CO 2 TEA laser. The initial dissociation step of the IRMPD of SiF 4 was found to be the decomposition into SiF 3 and F. The gas phase reactions of trifluorosilyl, SiF 3, with F and H 2 was investigated. A kinetic scheme was proposed to explain the experimental results. The set of coupled differential equations associated to this scheme was numerically solved. The rate constants of the SiF 3+F→SiF 4 and SiF 3+H 2→SiF 3H+H reactions were determined.

Laser induced breakdown spectroscopy characterization of Ca in a soil depth profile

Laser induced breakdown spectroscopy (LIBS) was used for the analysis of Ca in a soil depth profile of Patagonia (Argentina), using a CO 2 TEA Laser and solid pellets of the soil in a BaCl 2 matrix. The experimental set-up allowed for the simultaneous observation of the emission lines in the range 390–420 nm, corresponding to Ca(II) and Ba(II), so that the intensity ratio I(Ca)/ I(Ba) could be measured to obtain a calibration curve, rather than I(Ca) alone. The results of the ablation could be interpreted with an evaporation model and non-stoichiometric conditions. The experimental variables such as laser energy, number of pulses averaged, and Ca concentration in the pellet were evaluated in order to find the best conditions for the analysis. The samples were obtained at variable depths (from 0 to 18 m) and analyzed to measure the total Ca and the acid soluble Ca. These results were compared with those obtained with the standard techniques.

Progress in the development of a high average power ultra-broadband infrared radiation source

This paper describes numerical and analytical studies on the optimization of the ultra-broadband infrared (IR) source, a novel high average-power device. The main objective of current studies was the reduction of weight, size, and cost of the system by devising a scheme to generate the two closely spaced radiation lines with a single laser driver instead of the two CO/sub 2/ transversely excited atmospheric pressure (TEA) lasers envisioned in the initial work. By inducing the modulation instability in nonlinear media, we have obtained as good or better results as in our previous studies but with one of the TEA lasers replaced by a very low-power driver that provides the seed radiation for the excitation of the instability. Even more importantly, we have demonstrated that the second high peak-power TEA laser can be replaced by a compact, light weight, low peak-power driver by focusing the radiation to a tighter spot. The average power of the source is maintained at the previous level by operating at higher duty factor. In the new low-peak-power operating regime, the output spectrum is very similar to that of the high-power regime, provided that the ratio of the peak power to the nonlinear length that scales proportionally to the area of the laser spot remains fixed.

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 CO 2/N 2/He, at a 0.26/0.50/4.0 l min −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 cm 3 . 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.

Modeling of temperature fields in the graphite target at pulsed laser deposition of CN x films

The pulsed laser deposition (PLD) technique is frequently applied to synthesize carbon nitride coatings having a general formula CN x . In previous experiments, the polycrystalline CN x films were deposited with the use of a CO 2 TEA laser in a remote nitrogen atmosphere [1]. The x value was found to be approximately 0.6 and the grains, observed with SEM, were typically of a few hundreds of nanometers of size. This phenomenon was tentatively explained by the abundance of vapors generated by the action of the laser. It can be, in turn, related to the thermal fields in the graphite target. The numerical code ‘Fusion-2D’, describing laser/target interaction, was applied to model the temperature in two dimensions. The optical absorption data were taken for the wavelengths that corresponded to the typical lasers used in PLD processes, i.e. excimer, YAG and CO 2. The evolutions in the graphite target temperature at the pulses generated by these lasers were then calculated for a given power density. The differences in these evolutions were related to the volume of produced vapors and helped to explain the morphology of the synthesized films.

Dental hard tissue modification and removal using sealed transverse excited atmospheric-pressure lasers operating at lambda=9.6 and 10.6 microm.

Pulsed CO(2) lasers have been shown to be effective for both removal and modification of dental hard tissue for the treatment of dental caries. In this study, sealed transverse excited atmospheric pressure (TEA) laser systems optimally tuned to the highly absorbed 9.6 microm wavelength were investigated for application on dental hard tissue. Conventional TEA lasers produce an initial high energy spike at the beginning of the laser pulse of submicrosecond duration followed by a long tail of about 1-4 micros. The pulse duration is well matched to the 1-2 micros thermal relaxation time of the deposited laser energy at 9.6 microm and effectively heats the enamel to the temperatures required for surface modification at absorbed fluences of less than 0.5 J/cm(2). Thus, the heat deposition in the tooth and the corresponding risk of pulpal necrosis from excessive heat accumulation is minimized. At higher fluences, the high peak power of the laser pulse rapidly initiates a plasma that markedly reduces the ablation rate and efficiency, severely limiting applicability for hard tissue ablation. By lengthening the laser pulse to reduce the energy distributed in the initial high energy spike, the plasma threshold can be raised sufficiently to increase the ablation rate by an order of magnitude. This results in a practical and efficient CO(2) laser system for caries ablation and surface modification.

Dehydrochlorination of 1,2-Dichloropropane by CO2 Laser-Induced Breakdown; Comparison with Thermal Elimination

Dehydrochlorination of 1,2-dichloropropane (DCP) was conducted by thermal elimination and CO2 laser-induced dielectric breakdown, which was induced by focusing the 10.6 μm lines of a CO2 TEA laser. Thermal dehydrochlorination proceeded by a four-centered mechanism at > 425 °C and by a surface-catalyzed radical process at 2000 °C.

Earth-satellite-Earth laser long-path absorption experiment using the Retroreflector in Space (RIS) on the Advanced Earth Observing Satellite (ADEOS)

This paper reports the results of the laser long-path absorption experiments carried out with the Retroreflector in Space (RIS) on the Advanced Earth Observing Satellite (ADEOS). The RIS is a 0.5 m diameter single-element hollow retroreflector with a unique optical design which uses a curved mirror surface to correct velocity aberrations caused by the satellite movement. In the RIS experiments a laser beam was transmitted from a ground station, reflected by the RIS, and received back at the ground station. The absorption of the intervening atmosphere was measured in the round-trip optical path. After the launch of the ADEOS in August 1996, the optical characteristics of the RIS were tested, and it was confirmed that the RIS worked well in orbit. The spectroscopic measurement was carried out with the single-longitudinal-mode TEA lasers by means of the method utilizing the Doppler shift of the reflected beam caused by the movement of the satellite. The spectrum of ozone was successfully measured in the region, and the measurement of the column contents of ozone was validated with the simultaneous heterodyne spectrometer measurement. In June 1997, however, the experiment with the RIS was discontinued due to the malfunction of the ADEOS solar paddle.

The applicability of the Sedov - Taylor scaling during material removal of metals and oxide layers with pulsed and excimer laser radiation

For the removal of material with pulsed laser radiation the distance travelled by the shock or blast wave and the amount of energy released in the plasma state due to the absorption of laser radiation are determined experimentally and theoretically. The distance travelled by the blast wave is detected by schlieren photography, the released energy by monitoring the transmitted laser radiation during the removal process. The theoretical evaluation is performed by numerical simulation using a model incorporating the laser-induced vaporization process and the dynamics of the plasma state. The results obtained from the experiments and the model are compared with that of the Sedov - Taylor scaling. The removal of the oxide layer from austenitic steel is investigated with laser radiation produced by a TEA and a high-power laser device. For the TEA laser with fluences of 5 and 10 J 50 - 80% of the pulse energy is released into the plasma state and the Sedov - Taylor scaling describes the distance travelled by the blast wave in agreement with data from the experiments and the simulation. For the high-power laser with a fluence of 50 J , 6% of the pulse energy is released into the plasma state and the Sedov - Taylor scaling does not describe the data of the simulation. The process of removal of copper and aluminium material is simulated for excimer laser radiation with fluences of 15 and 30 J . For copper 15 - 30% of the pulse energy is released into the plasma state and the Sedov - Taylor scaling is applicable. For aluminium, less than 2% of the pulse energy is released into the plasma state and the Sedov - Taylor scaling is only applicable for the higher fluence.

Simultaneous emission of the HF and N/sub 2/ lines from a plasma cathode TEA laser

Simultaneous laser action from HF and N/sub 2/ is obtained, from a plasma cathode TEA laser, for the first time. The sliding discharge along the surface of a dielectric is used as a plasma cathode, for the main volumetric discharge. The laser operates at atmospheric pressure, with a gas mixture of SF/sub 6/:C/sub 3/H/sub 8/:N/sub 2/:He. For a typical flow rate ratio of 0.27:0.024:0.2:19.8 1 min/sup -1/, it produces simultaneously 160 mJ HF and 0.6 mJ N/sub 2/ laser outputs at 0.43% and 1.4/spl times/10/sup -3/% efficiencies respectively, at the moderate charging voltage of 28.5 kV. These output characteristics are obtained from a small active discharge volume and length of 10/sup 6/ cm/sup 3/ and 38 cm respectively. These values extend the performance, recently reported in the literature, of a sliding discharge HF/N/sub 2/ laser with corresponding simultaneous energy outputs of 12 mJ HF and 1.1 mJ N/sub 2/, to a higher energy output level, thus making the device suitable for a broader range of applications. This novel dual wavelength HF/N/sub 2/ laser system presented, can be particularly convenient for medical experiments, where the IR beam can be used for tissue ablation, while the UV beam can be used as the excitation source for fluorescence spectroscopic measurements, for the evaluation of the ablation process. Details are presented on the dependence of the laser performance parameters, such as output energy, discharge voltage and current and structure of the laser output pulses on the mixture composition and the circuit parameters.