K. M. Abramski

High-power two-dimensional waveguide CO/sub 2/ laser arrays

A two-dimensional, 39 element array of waveguide carbon dioxide lasers has produced a total CW laser power output of 750 W, using RF excitation of a compact, close packed assembly. Thermal effects associated with close-packing in the array are evaluated in terms of discharge wall temperature rise and cavity mirror distortion. The array elements are shown to have a 30% power derating relative to a single isolated laser channel, caused mainly by internal temperature rise. Mirror distortion and waveguide constructional errors do not degrade the beam quality of the array emission, which matches the theoretical value. However mirror distortion is shown to be responsible for a large spread in laser frequency between channels in the array. Based on the results, prospects are good for the construction of larger, multikilowatt incoherent arrays.

Single‐mode selection using coherent imaging within a slab waveguide CO2 laser

A technique for selecting a single high‐order lateral mode of a rf excited slab waveguide laser is described. An in‐cavity grid which matches the periodicity of the desired mode, together with slab waveguide dimensions which create coherent imaging by the Talbot effect, have produced a stable output power of 155 W in a high spectral purity, single‐resonator mode.

Phase‐locked CO2 laser array using diagonal coupling of waveguide channels

Continuous coupling of square‐bore CO2 waveguide lasers by geometrical overlap in the diagonal direction has been used for phase locking of a five‐channel array. A radio‐frequency discharge excited device has produced 125 W in phase‐locked operation, with power per channel equal to independent single channels. The dependence of phase‐locking range on the coupling geometry, and dimensional tolerances has been demonstrated. The array radiates approximately 65% of its power in the axial lobe.

Lateral and transverse mode properties of CO2 slab waveguide lasers

Abstract The output of a high Fresnel number, slab waveguide, carbon dioxide laser has been investigated for electrode gaps between 0.7 and 2.25 mm. The observed beam intensity patterns are found to be consistent with analysis in terms of high order rectangular waveguide modes. High order transverse mode suppression for gaps less than 1.5 mm has been attained and the lateral mode signature understood in terms of waveguide mode frequencies and spatial mode competition. Operation in a single EH 16,1 waveguide mode has been demonstrated. Output power for an 18 mm wide slab has been increased to 210 W at 1 mm electrode gap, corresponding to a specific power of 30 kW m -2 for planar, large electrode area, rf excited lasers. The cross-over between the effects of the (gap) -1 discharge scaling law and the (gap) -3 scaling of guide loss is shown to occur at ∼ 1.2 mm for aluminum electrodes.

Offset frequency stabilization of RF excited waveguide CO/sub 2/ laser arrays

A close-packed array of waveguide lasers provides an offset frequency which is inherently more stable than that from independent devices, and permits difference frequency tuning based on the tilting of a common resonator mirror. Examples are given for two- and three-channel arrays. Passive stability of the beat frequencies between channels generated by this tuning method is shown to be good, and for two channel arrays was further enhanced by using an electronic stabilization loop. A simple model of the control loop is formulated to express the relationship between the loop parameters and resultant improvement in frequency stability. The model parameters are compared to experimental results through Allan variance measurements. An Allan variance minimum of 20 Hz has been achieved for the two-channel system and areas for further improvements are considered. >

Discharge-induced frequency modulation of RF excited CO/sub 2/ waveguide lasers

The mechanisms causing a shift in the oscillation frequency of an RF-excited CO/sub 2/ waveguide laser through changes in the discharge excitation power are investigated. Frequency shifts in the range of +or-0.5 to 1 MHz per watt of RF input power were measured. These are shown to be consistent with the effects of thermal expansion of the laser gas caused by an increase of the gas temperature due to RF power absorption. It is also shown that the effects of gas dissociation are small but significant, whereas, contrary to earlier suggestions, the effects of electron density fluctuations are negligible. The discharge-induced frequency shift may be used as a simple frequency modulator with a frequency deviation of +or-30 MHz, although the usefulness of this effect is limited to a bandwidth of about 500 Hz, due to the acoustic resonance of the waveguide channel. >

Phase-locked operation of intersecting CO2 waveguide lasers by four-wave mixing

Abstract We report phase-locked operation of two carbon dioxide waveguide lasers induced by a process of four-wave mixing in an intracavity region where the two gain media intersect at an angle of 78 mrad. Mutually coherent output from the two lasers is observed with a locking range of 0.4 MHz, in agreement with estimates based on the gain saturation nonlinearity.

Single And Multi-Frequency Operation Of Tandem Waveguide CO[sub]2[/sub] Lasers

An array of waveguide lasers provides either multiple emitters with stable offset frequencies or a coherent, high brightness source when phase-locked.

Modeling of one-dimensional cavities for large-area gain media

We present a method and results of modeling of the large-area carbon-dioxide lasers, including gain saturation and dephasing effects. Numerical calculations are based on iterative evaluating of Fresnel-Kirchoff integral using fast convolution algorithm.