An independently adjustable multiline AM mode-locked TEA CO2laser

A new method is described for constructing an AM mode-locked, multiline TEA CO2laser oscillator generating nanosecond pulses. The multiline behavior is achieved by spatial separation of the rotational transitions at the amplifying medium. The setup generates 1.15 ns pulses with an energy of 3.7 mJ per pulse and containing simultaneously six rotational transitions in the 10.6 μmP-branch.     

High repetition rate TEA CO2laser

This correspondence reports on the successful operation of a TEA CO2laser at rates up to 1000 pps with an average output power up to 65 W over long periods of time. An essential feature of the present system is a rapid gas circulation transverse to the laser axis combined with a large volume of ambient gas. It is found that decomposition of the gas is one of the major problems at high repetition rates.     

A sealed high-repetition-rate TEA CO2laser

A compact atmospheric pressure CO2laser utilizing a double-discharge technique has been constructed and operated at repetition rates to 100 pulses/s. With the addition of small amounts of hydrogen and carbon monoxide to give a gas mixture of He:N2: CO2:CO:H2= 69.3:11:15:4:0.7, sealed operational lifetimes exceeding2 times 10^{6}pulses have been obtained. Operating in this mode, the output energy density is about 8-9 J/l at repetition frequencies of 30-40 pulses/s for input energy densities of 60-70 J/l. The operation of the sealed laser has been studied by means of mass spectroscopic measurements of the gas mixture. It has been determined that sealed operation is possible as long as the oxygen concentration is kept below 1-2 percent. It has also been found that the addition of small amounts of H2and CO will keep the oxygen concentration below 2 percent by reducing the CO2decomposition, allowing sealed operation. The experimental results are compared to the predictions of a theoretical model in which neutral and negative-ion processes have been included. The calculations indicate that when small amounts of oxygen or water are present in the discharge the negative-ion population is significantly increased and the ratio of negative-ions to electronsN_{n}/N_{e}can approach values near unity. These are the conditions under which discharge arcing was found to occur. The model also predicts that the dissociation equilibrium of the CO2can be controlled by the addition of the above concentrations of hydrogen and CO.     

Simultaneous CO and CO2laser

CW laser action at both the 5- and 10.6-μm wavelength regions has been achieved simultaneously from CO and CO2molecules in a slowly flowing mixture of He-air-CO. Two dc discharges through the premixed gases within a segmented laser cavity were used to provide molecular excitation and generate CO2molecules by discharge-initiated CO oxidation. Both liquid nitrogen and room-temperature water cooling were used concurrently. A total power of about 2 W has been achieved with approximately half the power in each wavelength region.     

Rotational transition competition in a single-mode CO2laser

In the present work we have investigated the mechanism of rotational transition competition of a single-mode laser by studying the effect of small variations of the out-coupling loss factor. For this purpose we used on the out-coupling side one extra mirror with a reflectivity of only 1 percent. In this way the instability problem could be followed with a controllable out-coupling device having a variable reflectivity between 73.6 and 81.5 percent and a corresponding variation in out-coupling loss factor. Due to the nonzero rotational relaxation time we find a narrow range of the gain-to-loss ratio of respective transitions to have nonsingle oscillations. We have observed single as well as multioscillating transitions as a function of the loss factor.     

Whispering-gallery CO2laser

The design and operation of a CW CO2laser based on the whispering-gallery principle is reported. The optical cavity consists of a portion of the equatorial region of a torus terminated by two flat mirrors. In agreement with theoretical expectations, the output beam is found to be TE polarized, and to consist of low-order Airy-Hermite-Gaussian modes.     

The transient evolution of AM mode locking a TEA CO2laser

The evolution of the pulse in an AM mode-locked TEA CO2laser has been investigated. The experiments have been performed by injecting the mode-locked pulses in a high-pressure slave oscillator at various time intervals after the initiation of the mode-lock process. This technique allows the measurements of the pulse widths independent on the pulse energies. A numerical solution of a dynamic model for the mode-locking process accurately predicts the transient evolution. It is shown that the build-up time to reach steady state can be, depending on the modulation depth, considerably larger than the duration of the pulse train.     

Second-harmonic generation in proustite with a CW CO2laser

The possibilities for nonlinear optics in proustite have been explored in a wavelength region previously indicated as having low absorption. We used a 10-W CW CO2laser oscillating on a single transition at 9.2-μ wavelength. The observed values for nonlinearity and absorption are, respectivley,(7.9 pm 2.0) times 10^{-23}in MKS units and 0.29 cm^-1.     

Q-switched CO2laser

Experimental studies of a rotating-mirrorQ-switched CO2laser have been undertaken to obtain high peak powers at 10.6-μ wavelength. TheQ-switched pulse has a temporal structure consisting of two intensity peaks and is similar to the temporal behavior of a slowQ-switched CO2laser. Based on the gas pressure dependence it appears that the pulse structure and duration are influenced by collision-induced relaxations of the laser medium. Using an oscillator-amplifier system peak powers of 120 kW with pulsewidths of 200 ns have been obtained.     

Theoretical and experimental studies of a multiline TEA CO2laser with hot CO2as an intracavity absorber

The multiline behavior of a ballast resistance helical TEA CO2laser incorporating hot CO2as an intracavity absorber has been studied. Simultaneous laser oscillation onP(16), P(18), andP(20)lines of 10.6 μm has been obtained reliably. A rate equation model has been developed for the hot CO2absorber and is incorporated with the model for the multiline TEA CO2laser for calculating laser intensities onP(16), P(18), P(20), andP(22)lines of the 10.6 μm band in the presence of the absorber. The theoretical calculations agree quite well with the experimental observations. These studies show that a hot CO2column of Proper length and temperature inside a TEA CO2laser cavity can produce simultaneous laser oscillation on at least three rotational linesP(16), P(18), andP(20)of the 10.6 μm band with almost equal intensity.     

Improved performance and rotational spectral characteristics of a doped helical TEA CO2laser

In this paper, we report significant improvement in laser energy, peak power, beam quality, and arc-free operating range of pressure in a helical TEA CO2laser using a small amount of additives with low ionization potentials. The increase in laser power was found to be considerably more than the corresponding increase in laser energy with the use of additives. In addition, we observed laser oscillation on many more rotational lines including the most dominant P(20) line than is normally observed in an undoped mixture. The relative energy on the P(20) line with respect to the total energy on the rest of the lines showed a maximal behavior with pressure in the range of 0.2-1.0 atm. This has been explained using a theoretical model which takes into account reduction in both the rotational relaxation time and the rise in laser gas temperature with the increase in gas pressure.     

Folded-path atmospheric-pressure CO2laser

A folded-path transversely excited atmospheric-pressure CO2laser utilizing shower or brush discharges is described. The output pulse has an initial peak 0.4 μs wide followed by a tail2-3 mus long. A peak power of 0.2 MW with 4.4 percent efficiency is obtained. By rotating one of the mirrors of the resonator the tail is eliminated, yielding a pulse 0.2 μs wide of the same peak power.     

Q-switching of the CO2laser

The laser pulses obtainable from aQ-switched CO2laser are calculated and compared with the results of a number of different techniques of performing theQ-switching. The continuously operating laser is considered first. The transition rates between the molecular vibrational states and their occupations are derived from the measured CW power. The laser tube was 1.9 meters long, had a diameter of 2.4 cm, and used flowing CO2-N2-He gas. For rapidQ-switching, maximum pulses of 4.5 mJ energy and 85 ns half width are predicted. Such pulses were observed with a rotating mirrorQ-switch. However, that technique has a limited pulse repetition rate and experiments on closely spaced pulses are difficult to interpret. A more flexible technique, which allows a much greater variation in the experimental parameters, is the use of a fast shutter to interrupt the laser beam in the cavity. While this switch is somewhat slower than the rotating mirror it does produce pulses of the same energy at repetition rates up to 5000 per second, and smaller pulses at any desired higher rate. From these measurements the upper and lower laser level lifetimes are deduced. They are found to agree well with the values obtained from the CW measurements.     

Single-frequency operation of a TEA CO2laser with a near orthogonally polarized injection signal

Injection mode selection of a TEA CO2laser was studied for injection signals polarized nearly orthogonal to the TEA laser output polarization. Single-mode operation was evaluated in an attempt to observe an anomalous effect attributable to the injection signal's polarization. The probabilities for single-mode operation were observed to be governed by the injection field component having minimum resonator loss.     

Operational characteristics of a PIE CO2laser

The design and operational characteristics of a high power pulser-sustained CW CO2laser is described. The "photoinitiated impulse-enhanced electrically excited" structure possesses operational features similar to an "electron beam-sustained" device and as such may provide a relatively simple and inexpensive alternative in high power CO2laser design.     

Thin film-coated waveguide CO2laser

A new type of radio frequency (RF) excited waveguide laser with a rectangular cross section is proposed which is composed of two dielectric or lossy materials and two metallic electrodes which are coated by a thin film with small absorptions. Theoretical and experimental analyses show that the maximum output powers of the new waveguide laser are much larger than those of conventional ones.     

Large aperture CO2laser discharges

Large aperture high-pressure gas laser discharges are a prerequisite for the development of high-energy gas lasers of sufficient power for the production of plasmas of thermonuclear interest. Of the several approaches being followed toward the attainment of such discharges, one utilizing weak volumetric preionization of the active gas region produced by UV radiation is described. The use of this technique has resulted in the successful generation of atmospheric-pressure CO2laser discharges between electrodes separated by 30 cm, having total cross sections of ∼600 cm². With input energies of ∼200 J/1 small signal gain values of 4-5 percent cm^-1were measured in 1 : 1 : 3 gas mixtures of CO2, N2, and He, respectively. It is thus concluded that this excitation technique could be incorporated into the fabrication of large volume gas laser amplifiers having beam cross sections in excess of 10³cm²and total output-energy capabilities ofsim 10^{4}J.     

Mixed isotope multiatmosphere CO2laser

A sealed transversely excited multiatmosphere pulsed laser is reported in which the active media is a combination of three isotopes:¹²C¹⁶O2,¹²C¹⁸O2, and¹²C¹⁶O¹⁸O. Lasing action is obtained on all 12 vibrational-rotational bands with continuous tuning observed between line centers at pressuresfrac{1}{2}tofrac{1}{4}of those required with conventional¹²C¹⁶O2lasers.     

Prediction of CO2laser signatures

Based on previous work, a method is presented to predict the signature of a CO2laser, i.e., the output power as a function of the cavity length. For that purpose the normalized laser intensity curve versus cavity length is determined for a single line. The calculation is based on a homogeneously broadened line (Lorentzian shape) and takes into account the line dispersion. The curve is a parabola and its shape is assumed as being the same for all lines considered. From calculated positions of line centers and small-signal-gain data the signature can be drawn with the help of a parabolic French curve. The transition from one line to the next is assumed to occur at crossings of the normalized intensity curves. The theory agrees well with the experiment.     

Dependence of injection locking of a TEA CO2laser on intensity of injected radiation

We report the results of an experimental study to determine the minimum required injected power to control the output frequency of a TEA CO2laser. A CW CO2waveguide laser was used as the injection oscillator. Both the power and the frequency of the injected radiation were varied, while the TEA reasonator cavity length was adjusted to match the frequency of the injected signal. Single-longitudinal mode (SLM) TEA laser radiation was produced for injected power levels which are several orders of magnitude below those previously reported. The ratio of SLM output power to injection power exceeded 10¹²at the lowest levels of injected intensity.