A microprocessor-controlled laser grating system for laser tuning

An apparatus for tuning a laser system to different wavelengths has been developed. The controlling electronics consists of a microprocessor and stepper motor combination utilized to control the angular position of a laser cavity grating. A resolution of 0.09° per step has been obtained. Convenient, accurate, remote tuning of a laser is achieved with the output wavelength displayed and/or retained in system memory.     

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.     

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.     

CO2 laser welding of copper slabs

For the first time it has been possible to laser weld copper sheets up to 3 mm thick with a 2 kW cw CO₂ laser. The main questions arising from the process are indicated.     

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.     

A continuously variable attenuator for the CO2 laser

A continuously variable attenuator for the CO₂ laser, causing minimal degradation of beam quality, is implemented using rotating ZnSe wedges, and is capable of transmissivities between 0.3% and 18%, and between 27% and 89%. The transmissivity at any particular setting was measured to be essentially constant for wavelengths from 9.27 μm (9R20) to 10.77 μm (10P36).     

A compact, highly stable CW CO2 laser without brewster windows

We describe an open resonator, quasi sealed-off; 70cm cavity length CO₂ laser with very high stability of power and frequency, which lases on 96 lines from 9R42 (2W) to 10P52 (5W) with a power of >11W on 9R20, 9P20, 10R20 and 10P20, plus on 18 hotband lines with ≈2W. This laser was used successfully to pump an FIR ring laser [1] enabling an FIR power stability of ΔP/P ≈ 10⁻⁴ by use of a simple PI control loop, thus demonstrating its superb frequency stability.     

Pulse behaviour of a compact RF discharged CO2 slab laser

We present the measurements made on a medium power, 35 cm long, radio-frequency discharge CO₂ slab laser operated in a pulsed regime obtained by switching the RF discharge. In this way, pulses with peak power up to 480 W at pulse repetition frequencies in the range 1 to 10 kHz have been obtained. Pulse energy and average extracted power have been experimentally characterized with respect to the pulse repetition frequency and to the pulse duration, and the pulse shape and characteristic times have been measured. We also investigated the propagation properties of the beam emerging from our laser.     

New CW FIR laser lines obtained in ammonia pumped by a CO2 laser, using the Stark tuning method

We report fifty seven CW FIR emissions observed in NH₃, by resonant pumping with a CO₂ laser. Exact coincidences between IR absorption lines of the gas and emission lines of the CO₂ laser have been carried out by Stark tuning. IR frequency shifts, up to 30 GHz, have allowed the pumping of forty three NH₃ transitions.These FIR emissions correspond to thirty one different wavelengths in the 50–400 m range; eighteen ones of them are new emitted wavelengths by pumping with the CO₂ laser.     

A tunable waveguide CO2 laser with expanded tuning range

A method of expanding the tuning range of the CW CO₂ waveguide laser making use of a Fabry-Perot type light modulator is proposed. A preliminary experiment has been done to confirm the workability of the proposed scheme.     

Mathematical modelling of gain-switched RF-excited CO2 waveguide laser

The detailed mathematical models for the evolution of light pulses in RF-excited CO2 waveguide lasers are derived. Explicit expressions for the pulse characteristics in RF-excited CO2 waveguide lasers are obtained. The effects of losses and unsaturated gain on output power are calculated.     

A cw CO2 laser rangefinder using heterodyne detection and on-off amplitude modulation

A CO₂ laser rangefinder has been built that uses an acousto-optic modulator to obtain an amplitude modulated optical beam from a cw laser. An on-off deflected beam was obtained by driving the modulator with a carrier modulated by a periodic binary code. The received infra-red radiation was heterodyne detected. After envelope detection of the heterodyne signal, the signal-to-noise ratio was improved by applying a digital integrator. Ranging was carried out by calculating the delay of the received code by means of a cross-correlation technique. For this purpose a minicomputer was implemented in the system. Using 1 W average beam power and measuring times less than 1 s, ranges of several kilometers have been determined from stationary targets.     

Temperature distribution along oversized hollow-core waveguides for CO2 laser radiation

Temperature distributions along various hollow waveguides are fully analysed experimentally when the waveguides are excited by CO₂ laser light. It is shown that the temperature decreases in an oscillatory manner along the waveguides due to the interference effect of guided modes. The distributors are well explained by a theory developed previously.     

In-process high power CO2 laser beam position sensing

The case for in-process sensing is one of the strengths of laser materials processing, both in the variety of signals obtainable from the process and the range of techniques for beam guidance. It is known that beam/nozzle alignment is of importance for high quality laser cutting. Thus, an in-process beam position sensing system was devised in this study as one of the potential tools for automation of the cutting process. Further, if the beam could be stabilized at a given location automatically this would be equivalent to relocating the laser beam. Laser beam position sensing is the first step towards this goal. The aim of this study is to create a beam position sensing system. This work presents a new approach using a rotating slit, a focusing lens and a photodetector. An automatic alignment procedure is also investigated.     

Multi-channel slab CO2 laser excitation with resonant cavities

A unique way of driving a multi-channel RF excited slab laser is presented. Resonant cavity techniques are employed to provide high power splitting and impedance transformation. Uniform and isolated power division was observed in eight discharge channels, stacked in a radial array, referred to as the Zodiac geometry. Impedance matching networks were not necessary as the RF cavity splitter creates a near ideal voltage source capable of driving any impedance. With 8 out of the 24 electrodes driven in the radial array, optical powers in excess of 1.2 kW have been observed at efficiencies of 12%.     

Short single-mode CO2 laser pulse generation by pulsed Q-switching

A simple method for the generation of short, single-mode CO₂ laser pulses produced by applying two voltage gates (of amplitude 3U_λ/4 and U_λ/4) to an electro-optic Q-switch placed in a three-mirror cavity is proposed. Single, single-mode, well-synchronizable pulses of 3 ns duration and of 3 mJ energy have been experimentally achieved from a TEA CO₂ laser with an intracavity Pockels cell with 3 ns switching time. Using a numerical simulation it is shown that with shorter switching time (≈1 ns) the method enables one to obtain, from such a laser, a single, megawatt pulse of 1 ns duration.     

Reconstructive microsurgery of the female reproductive tract using a CO2 laser

Laser tubal microsurgery was carried out on a sample of 82 patients. Employing current laser surgical systems, 21 conceptions occured in 20 patients, after limited exposure to conception risk during the 13-month study. This represents 48% of the 42 patients at risk. Tubal patency was demonstrated in 94% of the 82 cases. Based upon experience to date, more conceptions are expected as more patients become at risk and as exposure increases.     

The effects of power rippling on CO2 laser cutting

A power rippling method was proposed in this study to improve the cut edge quality by disturbing the natural frequency of the periodic striations in high power C0₂ laser cutting. A pilot study was also designed and set up to examine the power responsibility of the laser system, which is externally controlled by a modulated analogue signal from a signal generator. Several aspects were examined in this study. The effects of different power rippling frequencies on the cut surface roughness is the first such aspect, and the different power modulation depth on cut surface roughness is another. The power rippling shape is the third important parameter examined in this study. It was found that the amplitude and frequency of the striation pattern on the cut surface were significantly affected by the characteristics of the rippling power. Cutting quality can be significantly improved by rippling the laser power.