CO2/CO2 isotopic ratio measurements with a continuous-wave quantum cascade laser in exhaled breath

A laser spectrometer based on a continuous-wave thermoelectrically-cooled distributed feedback quantum cascade laser at ∼2308 cm⁻¹ has been evaluated for measurement of ¹³CO₂/¹²CO₂ isotopic ratio (δ¹³C) changes in exhaled breath samples and in CO₂ gas flows in the concentration range 1-5%. Mid-infrared CO₂ absorption spectra were measured in a 54.2-cm long optical cell using balanced detection whereby the beam passing through the cell was ratioed against a reference beam split-off from the main beam before the cell. Signal-to-noise ratios (SNR) were estimated for CO₂ concentration measurements determined from either absorption peak amplitude or absorption peak area. The highest SNR were achieved in the measurements based upon a fitted absorption peak area. Typical short-term δ¹³C precisions of 1.1⁰/₀₀ (1-s integration time) and 0.5⁰/₀₀ (8-12-s integration time) were estimated from the two-sample (Allan) variance plots of data recorded in the optical cell at a pressure of 20 Torr and with no active temperature stabilization of the cell and gas flow. The best precision of 0.12⁰/₀₀ was achieved for averaging 80 successive 1-s integration time measurements.     

Reflectivity measurements of a CO2 laser produced plasma

Reflectivity measurements on a CO₂ laser produced plasma are presented and results are compared with the conflicting results of other recent papers. The results presented here show strong anomalous absorption above an irradiance level of ～4 × 10¹⁰W cm^-2 which is a factor of two lower than is predicted from the theory of the parametric instability.     

Reflectivity measurements from a nanosecond CO2 laser produced plasma

The back-scattered light from a laser produced plasma has been studied using a nanosecond gigawatt CO₂ laser. The spectral shift and width of the reflected light have been determined as a function of the incident laser energy.     

Time-dependent interaction of pulsed CO2 laser radiation with liquids

Many industrial applications of high-power lasers involve the creation by vaporization of a keyhole in a solid target. This structure is unstable with respect to collapse and can be maintained only by achieving a balance between pressure terms from laser vaporization and those of surface tension and hydrostatics. In addition, liquid flow and plasma effects also modulate the laser beam intensity resulting in a complex feedback system in coupling laser radiation into the target. In this paper, we report data obtained on the time dependence of structures associated with laser drilling of an absorbing liquid. These data, obtained at low incident laser intensities in the absence of plasma effects, show the complex nature of the laser-keyhole interaction even in a two-phase system. Some results of experiments carried out in low gravity are also presented.     

Current CO2 laser surgery

With the development of suitable instrumentation, human-engineered to fulfil the requirements of the clinical surgeon and designed to fit in with the physical conditions prevailing in the operating theatre, laser surgery has advanced rapidly in the past few years. It shows signs of even more rapid progress and general acceptance as its application and advantages in more and more fields of surgery are demonstrated.     

Advanced CO2 laser rangefinders

Factors affecting the design of compact heterodyne- and direct-detection systems are contrasted. Recent UK achievements are placed in context: a TEA laser direct-detection rangefinder and a chirp-pulse-comparison rangefinder-velocimeter are described.     

Absolute frequencies of CO2 laser transitions by multiplication of CO2 laser difference frequencies

Frequencies of CO₂ laser transitions have been compared to the Cs standard by a four-step frequency chain using difference-frequencies from five CO₂ isotope lasers. A tungsten-nickel diode generates the differences and their harmonics. Measurement of the 10.71 μm R(6) transition of ¹³C¹⁸O₂ is described. The absolute frequency was found to be 27 979 469.512(65) MHz. Simultaneously, the four other CO₂ frequencies in the chain were also determined.     

Energy balance measurements on a nanosecond CO2 laser created plasma

Interaction of nanosecond CO₂ laser radiation with a solid deuterium target has been investigated with incident laser fluxes up to several times 10¹²W/cm². Reflection, X-ray and ion measurements were performed at different angles in the relevant half-space around the target. The energy balance deduced from reflection and ion time-of-flight measurements led to a total integrated reflectivity of 60 to 80%. Fast D⁺ ions with kinetic energies as high as 40 keV were detected and identified. Hard X-rays were observed in the range of 1 to 10 keV. A discussion of these results is presented.     

Pulsed inductive discharge CO2 laser

A pulsed inductive discharge CO₂ laser with a wavelength of 10.6 μm has been created for the first time. The excitation system of a cylindrical pulsed inductive discharge (pulsed inductively coupled plasma) in the gas mixture of CO₂:N₂:He was developed. The temporal and energy parameters of the laser radiation were investigated. The maximum inductive discharge CO₂ laser radiation energy of 104 mJ was achieved. An average power of 3.2 W was obtained at laser generation energy of 65 mJ and pulse repetition rate of 50 Hz. In the cross-section, the laser radiation had the ring shape with an external diameter of 34 mm and thickness of 4-5 mm. The measured divergence of laser radiation was 12 mrad.     

CO2 laser cutting of slate

Slate is a natural stone which has the characteristic that shows a well-developed defoliation plane, allowing to easily split it in plates parallel to that plane which are particularly used as tiles for roof building. At present, the manufacturing of slate is mostly manual, being noisy, powdery and unsafe for the worker. Thus, there is a need to introduce new processing methods in order to improve both the working conditions and the quality of the products made of slate.Following the previous work focused on the drilling and cutting of slate tiles using a Nd : YAG laser, we present in this paper the results of the work carried out to explore the possibilities to cut slate plates by using a CO₂ laser. A 1.5 kW CO₂ laser was used to perform different experiments in which, the influence of some processing parameters (average power, assist gas pressure) on the geometry and quality of the cut was studied. The results obtained show that the CO₂ laser is a feasible tool for a successful cutting of slate.     

Studies on CO2 laser marking

The nature of CO₂ laser marking was studied with a view to putting these lasers to practical use in the semiconductor industry. The marking is found to be due to surface spattering rather than burning, which is the main factor in YAG laser marking. The visibility greatly increases by the application of a surface treatment such as marker ink, varnish or poster color. The CO₂ laser may therefore be used in place of the YAG laser, now widely used for marking, with some merits: CO₂ laser marking is cheaper and faster, and in addition there is no danger of injury from irradiating laser light.     

Raman intensity measurements of the Fermi diad ν1, 2ν2 in CO2 and CO2

Intensity measurements of the ν₁, 2ν₂ vibrational Raman bands of ¹²CO₂ and ¹³CO₂ lend support to Amat's suggestion that the unperturbed 02⁰0 level is above the 10⁰0 level for ¹²CO₂. For ¹³CO₂, however, the ordering of the levels is reversed.     

Nonlinear interaction of CO2 laser radiation with aluminum and polyethylene targets

The characteristics of A1 and (CH₂)_n plasmas produced by a high-power CO₂ laser are investigated over the flux range 10¹⁰-5 × 10¹¹W/cm² where absorption processes other than simple inverse Bremsstrahlung are active. The threshold dependent behavior of the measured plasma parameters indicates the presence of the parmetric decay instability.     

AC-chopper application for CW CO2 laser

A microprocessor-based algorithm was developed to control the power supply to a CO₂ laser using an AC-chopper method. This system was connected directly to a CO₂ laser tube without the need for a dc-dc converter or the storage capacitance of a multilevel circuit. The typical CO₂ laser power supply system had a full-bridge series resonant inverter or voltage multiplier. AC-to-AC converter schemes using zero voltage switching (ZVS) can be used efficiently and economically for low and medium power applications.This paper reports the performance characteristics of a symmetrical AC-chopper technology that can maintain the quality of the ac output of a CO₂ laser tube, regardless of the amount of switching loss. The laser was operated to an output power, maximum system efficiency total gas mixture of 37.2 W, 92%, and CO₂:N₂:He=1:9:15, respectively. The laser system, AC-chopper power supply and its operation were examined.     

Optically pumped NH3 laser using a continuously tunable CO2 laser

The use of a continuously tunable CO₂ laser to optically pump the NH₃ laser via previously inaccessible absorption lines is described. Efficient laser action has thus been achieved in the 11–13 μm region on transitions formerly only obtained in buffered mixtures.     

Phase-locking of axisymmetrical-fold combination CO2 laser

Two new methods for phase-locking are used in the axisymmetrical-fold combination CO₂ laser. We demonstrate the feasibility of two methods by theoretical deduction, and give the light intensity distribution of far field by numerical simulation. When phase is locked, the axisymmetrical-fold combination CO₂ laser can provide a high output power with good beam quality. Furthermore, the peak light intensity of output beam with phase-locking is obviously higher than that without phase-locking.     

Mathematical modeling of CO2 TEA laser

Five and six-temperature models for the CO₂–N₂–He system are used to describe the process of the dynamic emission in the TEA CO₂ laser. All physical constants and relaxation rates related to these models are examined to estimate the output pulse parameters as a function of the input parameters. The two pumping processes implemented; empirical function and differential equation show a good agreement with the experimental data.