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An investigation was made of the emission spectrum of an electric ionlzation high-pressure CO2 laser. The four strongest vibration-rotational transitions were active in a resonator without a dispersive element. The intensities of the lines fluctuated strongly though the total output was relatively stable. Interferometric measurements of the spectral width of the P(20) lines of the 000–1000 band were carried out in a plane-parallel dispersive resonator with a diffraction grating. The width of this line increased with the gas pressure and with the excess of the pumping level over the threshold.

To find a technique which will permit a quick bloodless primary excision of an acute burn, through hyperaemic tissues, experiments have been conducted in the laser excision of thermal burns of the white rat and the miniature pig. The animals were burned, excised by carbon dioxide laser, argon laser, cold-knife scalpel or Bovie electric scalpel, and grafted. Burns were successfully excised with minimal blood loss using the lasers, but there was no significant difference in haematocrit, WBC, total protein or weight values between the laser-excised rats and those excised by Bovie or cold-knife scalpel. There was little difference between take and survival of grafts in the Bovie, cold-knife and laser series, but there were marked differences between the thermally excised and cold-knife excised burns in the ability of epithelial islands of the burn area to grow out and cover the lost-graft areas. Differences were found in the coverage of burns between the white rat and the miniature pig.

A mass spectrometer was used to study atomic oxygen recombination following pulsed electrical discharges through O2, CO2 and a CO2-N2-He mixture, at pressures of a few torr. The surface recombination coefficient gamma for atomic oxygen in a pyrex discharge tube was found to be in the range 2.6*10-4-5.2*10-4, which is about an order of magnitude larger than previously determined values. For sealed CO2-N2-He lasers at pressures below 50 Torr the homogeneous recombination rate should be small compared with the surface recombination rate.

A description is given of a method for the stabilization of the emission frequency of a CO2 laser based on the use of narrow resonances in the absorption line of an external molecular (SF6) low-pressure cell operated under saturation absorption conditions. The relative stability of the frequencies of two independently stabilized CO2 lasers was 310–11 in 10 min. The upper limit of the collision-induced frequency shift was determined for a vibration-rotational transition in the SF6 molecule: This shift did not exceed 300 Hz/mtorr. An analysis was made of the effects influencing the frequency instability under experimental conditions and methods for improving the stability and reproducibility of the laser frequency were considered.

In this study the measured rate of healing of identical excisional wounds produced by the carbon dioxide laser and three other surgical modalities, viz.: conventional scalpel blade, electrosurgical (Bovie) unit, and plasma torch are compared. Differences in the gross and microscopic findings are discussed and partially explained. These studies would indicate that portable and easily controllable lasers have the potentiality of becoming a new type of practical surgical-knife and haemostatic instrument.

Endotracheal and endobronchial carbon dioxide laser surgery can be carried out using standard ventilating bronchoscopes, a recently developed laser endoscope attachment and a 50W CO2 surgical laser unit. General anesthesia, using nonflammable anesthetics, is delivered through the side arm of the ventilating bronchoscope; the tidal flow of gases keeps the trachea and bronchi free of steam and smoke. The technique has been particularly helpful in the bloodless removal of recurrent papillomas from the trachea and main stem bronchi of ten children with tracheostomies. While three of the patients have gone into remission following laser excision, the method cannot be curative of itself. There were no complications attributable to the carbon dioxide laser surgery, per se, but constant vigilance must be exercised as with all laser surgery. As instrumentation becomes refined the technique will have wider application in the management of tracheobronchial disease.

Excitation by a carbon dioxide laser has been used to obtain the infra-red emission spectra of a number of gaseous aliphatic hydrocarbons. The experimental set-up is described and the spectra obtained are correlated with bond vibrations and are shown to be similar to infra-red absorption spectra. The future requirements of this technique are discussed and its analytical possibilities are indicated.

Extracted human teeth were exposed to continuous CO2 laser radiation at 10.6μ. Ground sections showed disrupted enamel rods and incineration of odontoblastic processes in dentin. Microradiographs of enamel confirmed the changes observed, which were probably due to high temperature elevation at the site of interaction together with heat flow from this region.

The healing of surgical incisions made with a carbon-dioxide laser, cutting diathermy, and scalpel has been compared. Laser and diathermy incisions of skin healed more slowly than scalpel wounds, but no such delay occurred in incisions of the abdominal wall. It is suggested that the differences result from terminal necrosis of the wound edges and variations in the sequence of wound repair.

Scanning electron microscopic observations of the pulsed carbon dioxide laser effect on human enamel support microradiographic findings and indicate that this laser is significantly more efficient than the ruby laser within the limits of this investigation. Surface changes which were suggestive of fusion occurred between energy densities of 13 to 50 joules per square centimeter.

An intracavity Fresnel loss-plate technique of measuring gain characteristics of a laser is described. The technique is applied to the CO2 laser and the results are found to agree well with other published measurements.The saturation parameter of the CO2 laser is found to increase with laser discharge current.

Rods of pyrolytic carbon several centimeters long with submillimeter diameters were grown in an atmosphere of flowing gaseous hydrocarbon by heating with a focused CO 2 laser. The carbon deposits with the average c-direction along the axis of the rod.

Partial hepatectomy by means of a carbon-dioxide laser has been performed in 13 dogs. The operative technique is described, and its advantages and the absence of morbidity and mortality during the 10 weeks after operation are discussed.

A self-contained portable apparatus comprising a continuous single-mode carbon dioxide laser with an articulated arm and manipulator with interchangeable attachments designed for clinical surgery is described and illustrated. The application of this instrument to various plastic surgical procedures in the light of past experience is discussed.

A bibliography concerning carbon dioxide lasers has been compiled covering the period 1964 through 1969. The chronologically listed references have also been catalogued into an author index and a subject index.

The principles governing the mode of action of carbon dioxide lasers are briefly reviewed. A modular form of CO 2 -N 2 -He system using commercially available glass pipeline units is described and factors influencing design and operational procedures discussed. Measurements are reported on the effect of plasma tube current, pressure and gas mixture flow rate on power output and the results are analysed with reference to known gain data published for this type of laser. The system described produced 16 W CW stable power output from a 3 mm diameter coupling hole. Methods for improving this performance are suggested.

Power of 20 mW and gain of 11% have been obtained by using thermally excited nitrogen to pump a flowing‐gas carbon dioxide laser. One immediate use of this new pumping technique is the study of molecular laser physics in a simplified environment; the thermal laser is essentially free of chemical and charged‐particle effects.

A monomode carbon dioxide laser, delivering a constant power on any rotational line of either the 10.4-μ or the 9.4-μ band, has been achieved by control of the cavity frequency and of the gain. A piezoelectric ceramic has been used either for a frequency sweep of the cavity or for output stabilization at the bottom of the Lamb dip. This laser has been used for two studies.

Ablative materials performance in high radiative heat flux environments produced by CW carbon dioxide laser

The saturated gain constant of the carbon dioxide laser is calculated using a thermodynamic approach. At low electron densities the gain constant is found to saturate according to a well-known and simple function. At higher electron densities, however, a more complicated form is assumed. The calculations are found to agree well with measured saturated gain.

Concrete is a stubborn material to break down and remove, for example in demolition work, but its low thermal conductivity may make it susceptible to breaking by laser. The authors describe here tests with different methods, notably by thermal shock, and forecast the development of a portable carbon dioxide laser tool for site use.

The pathological effects upon the eye of exposure to infrared laser radiation emitted by a carbon dioxide (CO 2 ) laser, was studied. A total of 142 rabbit eyes was irradiated at varying dose levels, and each was observed for a period of two months. Within the limits of the power outputs and exposure times considered, clinically detectable ocular damage was limited to the cornea. Five clinical levels of corneal injury were defined, and the dosage of CO 2 laser radiation capable of producing each level of injury was determined.

A description is given of a 10-liter electron-beam-controlled CO2 laser operating at atmospheric pressure and emitting pulses at a repetition frequency of 5 Hz. The specific energy output of this laser is 0.015 J/cm3 and the efficiency is 10%.

A theoretical investigation is made of the amplification in a transverse-flow CO2 laser. It is shown that the energy efficiency of a laser system with a multipass amplifier may be higher than the efficiency under oscillation conditions.

Measurements were made of the temperatures of the deformation vibrations of the CO2 molecules by the method of reversal of spectral lines in the 15 μ region. A comparison of the vibrational temperatures obtained in this way with the calculated temperatures of the gas indicated that the population of the lower laser level was in equilibrium. Parallel measurements of the temperature of the antisymmetric vibrations of the CO2 molecules made it possible to determine the absolute populations of the laser levels and the population inversion. A comparison was made with the results obtained by the method of amplification of a laser signal.

Modulation of 10.4 μ carbon dioxide laser radiation has been obtained by the application of the Stark effect in several molecular absorbers. The depth of modulation obtained has been measured as a function of modulator gas pressure and incident light intensity. The results show an absence of saturation effects over the intensity range investigated.

The haemostatic property of carbon-dioxide laser radiation has been compared with conventional cutting diathermy for experimental partial hepatectomy. The superiority of the laser in reducing haemorrhage from the liver is demonstrated, and possible clinical applications are suggested.

Techniques for the application of the carbon dioxide laser to laryngeal surgery are outlined and include operative and anesthetic management. Laser surgery teaches improved surgical judgment in and application of conventional procedures. The lack of trauma, the degree of precision and the speed of healing as seen in one year of experience indicate the results of laser surgery to be superior to conventional techniques in the treatment of papilloma, polyps, polypoid degeneration, hyperkeratosis and carcinoma in situ. A family of laryngeal retractors is introduced whose utilization with intralaryngeal mirrors makes essentially all areas of the larynx accessible for lasing.

Ablative materials performance in high radiative heat flux environments produced by CW carbon dioxide laser

It appears that the two most sensitive infrared receptors known in the biological world are found in two widely different families of snakes, the pit vipers and the boas. After an infrared stimulus from a carbon dioxide laser, which has a monochromatic output at 10.6 micrometers, we find evoked potentials in boas with chronically implanted electrodes. Our data suggest that the receptors operate on a thermal principle.

In preliminary studies, the carbon dioxide laser with a specially devised surgical manipulator has been shown to have a great potential for surgical application, especially in neurosurgery. It can incise nearly all tissues, bore or drill, excise and vaporize as needed. Cancers, even when ulcerated and infected, can be made to disappear by vaporization or portions of neoplasms can be excised with the laser beam. Experimental, transplantable animal tumours and one human brain tumour have already been treated with this laser. Rapid cleaning of infected, scarred decubitus ulcers, followed by immediate placement of free or pedicle grafts is suggested as a means for eliminating the weeks of pre-operative preparation ordinarily necessary in such cases. Minimal lesions can likewise be made for functional neurosurgery or for other purposes. When used in conjunction with the operating microscope control is correspondingly increased. Action by the laser is swift, gentle and easily controlled. Damage from the beam can be confined to within a millimetre of its application. Small blood vessels are readily coagulated by the CO2 laser making oozing surfaces easier to handle. The disadvantages include the inability of the CO2 laser beam to traverse any tissue, including the transparent media of the eye, without damage. Deep structures must, therefore, be surgically exposed. Ignition of flammable materials, such as drapes, and damage to personnel must be prevented but this can be done quite simply. Among the many problems which remain are those related to the total removal of cancers without causing undue damage to surrounding structures and those related to wound healing especially for skin. The problem of bleeding from large vessels needs further study. A method for controlling the vaporization of neoplasms, using radioactive monitoring of the smoke produced, is suggested.

THE radiation produced by a carbon dioxide laser can destroy tissue1–3; exposure to the unfocused beam results in a superficial lesion which develops the characteristics of a burn: erythema, oedema, blistering and charring. If the beam is focused to a spot of 1–2 mm in diameter it incises tissue to a depth of several millimetres, depending on the laser power and focus cone angle and the speed of incision4, but no visible damage is caused to adjacent tissues.

It is, of course, necessary to know the output of the laser. In the biomedical field it is much more important to be precise and accurate. The laser reaction in living tissue changes with but small changes in the various parameters of the laser output, whether it be changes in power, energy outputs or pulse duration. The findings of laser research at various centers cannot be compared unless accurate outputs of laser radiation are made. This important field is in a very much confused state at the present time because of the difficulty of measurement of laser output, especially of high outputs. Exit energies above 1500 joules exit energy have been used in biomedical applications with the pulsed solid-state lasers, 0.5–10 watts power outputs are to be used for the argon laser and 25 watts for the carbon dioxide laser. It would seem, at first glance, that the problem of measurements should be simple, for it is merely the detection of classical changes in electromagnetic fields. Many studies of this problem have been done in our laboratory by Hornby and Rockwell.

FOUR years ago, investigations on carbon dioxide laser surgery were initiated in our laboratory. This laser was relatively inexpensive by comparison with ion lasers, the only other high output continuous wave (CW) lasers with surgical potential. The CO2 laser could be coupled with beam guides used as manipulators, was flexible, had a high efficiency and provided the continuous wave (CW) power needed for an “optical knife”. One disadvantage was, of course, the output of an invisible beam far out in the infrared at 10,600 nm and the consequent expensive infrared optics required. The safety programme for investigative laser surgery has been reported before by our laboratory1. Specific hazards for the high output CO2 laser arise from the reflexions from target areas and from surgical instruments. Our initial surgical experiments with 25 W output (Perkin Elmer CO2 laser) were done on metastatic melanoma of man. Non-specific thermal coagulation necrosis developed after laser surgery. There was no local dissemination of tissue fragments from the CO2 laser.

Basalts heated strongly with focused infrared laser radiation vaporized and splattered. Electron microprobe analyses of condensate, ejecta, and residue show strong vapor fractionation trends which, for some elements, are different from what would be expected theoretically and from previously reported data on more siliceous materials. It appears that solution effects can account for these differences. Heating of materials by a powerful focused laser beam for the purpose of study of vapor fractionation is a convenient technique that is more versatile than previous methods such as heating in solar or arc image furnaces.

In experiments on dogs, a focused beam from a continuous wave surgical carbon dioxide laser integrated with an operating microscope was used selectively to evaporate predetermined amounts of normal vocal cord tissue through a laryngoscope. This mode of tissue removal was precise, rapid and practically bloodless. Microscopic laryngoscopy examinations and histological work-up one, two and three weeks postoperatively indicated normal healing similar to that of clean surgical wounds.

Maiman's discovery of the laser in 1960 1 led to many technical advances. Field use of lasers has become widespread, and medical institutions are installing laser devices for clinical or research use. As the use of high-power lasers, particularly those that function continuously, becomes more extensive, accidental or intentional exposure will, of course, increase. The possibility of detrimental effects as a result of such exposures is a serious hazard. Recently, considerable work has been done with continuous wave (CW) gas lasers containing carbon dioxide and nitrogen. Relatively high power has been achieved with these devices; continuous power output exceeding 2,500 ws has been reported, and much higher outputs are within the present state of the art. 2 These potential hazards prompted us to study the biologic effects of exposure of living animals to CO 2 laser radiation. Unique Characteristics of the CO2 Laser The CO 2 gas laser possesses