Laser Power Measurements Research Articles

Laser power and gain measurements on the sequence bands of CO2

An experimental technique is reported which converts a conventional cw CO2 laser into one which lases on a series of new laser bands. These bands are identified as the (0002–[1001,0201]I,II) and the (0003–[1002,0202]I,II) sequence bands of CO2, and lie in the 10-μm wavelength region. The technique involves placing a cell containing hot CO2 in the laser cavity to suppress the regular 0001 bands. We report the first detailed power and gain measurements on the new laser bands. More than 80 laser lines have been observed in the 0002 bands, with cw output powers as high as 10 W. Gain measurements are reported for a variety of discharge conditions, and gain coefficients greater than 0.3%/cm have been obtained. We have also observed several laser lines in the 0003 sequence band of CO2. Possible applications of the new laser lines are discussed, particularly their use in determining vibrational temperatures in CO2 discharges.

New detector for laser power measurement

A thermoelectric detector is described for measuring the output power of a CO2 laser from 1 to about 30 or 40 W. Its response time can be less than 1 s, with convenient sensitivity, adjusted according to the power range.

Limitations of the Use of Vacuum Photodiodes in Instruments for the Measurement of Laser Power and Energy

The effect of the variation in the area sensitivity upon the calibration of instruments incorporating biplanar vacuum photodiodes for the measurement of laser power and energy is discussed. A technique for the measurement of the area sensitivity is described, and the experimental results for several tubes are given. At the present time it would appear to be difficult to use biplanar vacuum phctodiodes in devices to measure laser energy or power.

Calorimetric measurements of laser energy and power

The use of calorimeters for measuring laser output energies and powers is broadly reviewed. Instruments are categorized as disc, cone, hollow-sphere, bolometer, volume-absorption, and partial absorption types.

Utilization of optical detection in measuring laser power output

Certain features of optical detection (rectification) are considered in relation to the use of this phenomenon in measuring laser power output. The results are given of an experimental investigation of several crystals and of the principal characteristics of a transmission-type device for measuring peak power.

Calorimetric Measurement of Optical Power from Pulsed Lasers

Laser power measurement instrumentation, the standards used, and the techniques are described. Average power can be measured with an accuracy approaching ± 1.2 percent using the international joule or electrical watt as the standard for calibration of the system. A determination of peak power can be made from the measurement of average power, repetition rate, and a knowledge of the power-time function. Automatic data acquisition and a time-share computer are used for data reduction.

Laser Energy and Power Measurement with a Double Reflecting Plate Calorimeter

In a double reflecting plate calorimeter, the energy from a laser beam is partially absorbed by metal mirrors. The rest is reflected through an exit where it is free to interact with some medium. Characteristics of this calorimeter with a pair of aluminum plate mirrors are (1) wavelength range ∼0.1−∼1 μ, (2) energy input range ∼0.1−∼50 J/cm2 (pulsed normal mode) and estimated power ∼100−∼1000 MW/cm2 (pulsed Q switched) depending upon energy density, (3) estimated error ±2% over most of the ranges given, (4) 5 sec for the plates to reach a uniform temperature and to make measurements, and 2–4 min required cooling time between inputs, and (5) both absorption and reflection determined from plate calorimetric data. The sensitivity and the wavelength, energy, and power ranges may be increased by using different plate dimensions and materials. Data from an intercomparison between this calorimeter and an NBS liquid cell calorimeter yield agreement of about 0.6% at 0.6943 μ. The light was p polarized (electric vector parallel to the plane of incidence). The energy of the components of polarization parallel and perpendicular to the plane of incidence of a light beam may be evaluated.

An automatic linearity tester for photodetectors

The apparatus is designed to measure the properties of photodetectors used for the measurement of pulsed laser power and energy. Repetitively pulsed lasers at 0694, 091, 106 μm are used to give pulse lengths in the range 5-400 ns. The beam power is varied by a slowly rotating polarizer and, after division, produces photocurrents in both the test cell and a standard monitor cell. The signals are integrated electronically and used to produce Y and X deflections of a cathode ray oscilloscope spot. The spot is brightened after a few microseconds to give a point on a plot of photoelectric charge against pulse energy. Alternatively, the test cell output is time-sampled electronically to give a plot of photocurrent against pulse energy (or power). Departures from linearity of 3% can be detected over a range of 105 in photoelectric charge with better accuracy for smaller ranges. For the GaAs laser at 091 μm a single optical pulse, of approximately 30 ps long, can be generated. This is used for rise-time measurements.

Theory of Isoperibol Calorimetry for Laser Power and Energy Measurements

Laser power and energy measurements are commonly made in calorimeters operating in a constant temperature environment. Calorimeters of this type are analyzed in terms of the first law of thermodynamics and the boundary value problem describing heat flow in the calorimeter. This theory of the measurement suggests design features of the calorimeter, sources of error to be avoided in design and operation, and tests to demonstrate experimentally the adequacy of the design. The analysis shows how time—temperature data can be used to allow for the temperature gradient on the calorimeter and the heat exchange due to transients in the temperature.

Laser Power and Energy Measurements

Laser Power and Energy Measurements

Technology in brief

A calorimeter to measure laser power over a wide range is described by E. Bayer and G. Schaak, of the Technische Hochschule at Darmstadt in Germany, in the Journal of Scientific Instruments Ser. 2, 2, 208 (1969). Damage to materials by the absorption of laser light has been the chief drawback to other devices for measuring laser power, such as absorption on a blackened cone or sheet, absorption in wire causing a change of resistance, and diffuse reflection from a Lambert surface.

Design and performance of photo-cell systems for pulsed laser power and energy measurements

The optical and electrical problems in the design of a beam-sampling detector for laser power, energy and pulse duration measurements are discussed with a view to achieving an accuracy of 2% relative to a fundamental detector for pulses down to 3 nsec duration. Experiments show that a beam sampler using an ITT F4000 biplanar vacuum cell mounted in a coaxial taper is capable of this accuracy, but that the silicon diodes (EG + G SD100, Mullard BPY13A) trap some of the photoelectric charge and then release it with a time constant of up to a few microseconds giving a pulse length-dependent sensitivity: they can be used for energy measurements, however. The Mullard 90CV vacuum photo-cell holds back about 6% of the photo-electric charge for about 1μsec and can also give erratic currents up to ten times the computed saturation current: effects probably due to residual gas in the cell. The limits set on performance by the rise time and maximum linear current of the various detectors are discussed. The design of a holder for the ITT F4000 photo-cell giving a rise time constant of 0.25 nsec is given.

Measurement of Far-Infrared Laser Power

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Wire cone calorimeter for absolute laser continuous wave radiation-power measurements

In the paper a method of absolute measurements of continuous wave laser power is described. The influence of the apex angle and the walls smoothness on the reflection coefficient of the cone absorbers has been investigated. The construction and electrical circuit of a calorimeter containing a wire cone absorber are also described. This is designed for radiation measurements in the range from 25 μW to 25 mW.

Paper 7: Laser Power and Energy Measurement by Photoelectric Techniques

The use of photoelectric devices for measuring the output power and energy of pulsed and c.w. lasers is well established. This paper describes the principles, limitations, and advantages of the method. The precautions which must be taken to ensure accurate and reproducible results are also discussed in some detail.

Wire calorimeter for absolute and accurate laser-power measurements

A calorimeter, acting in a self-balancing bridge circuit and designed for absolute measurements of radiation power from continuous-wave lasers, is described. The calorimeter contains a wire-cone absorber with an effective absorptivity of 99.5±0.2%. The arrangement, consisting of a d.c. bridge, a galvanometer amplifier and a transistor current regulator, is suitable for absolute-power measurements in the range 30μW to 30mW with an accuracy of within 1%.

Measurement of laser energy and power

Measurements of laser energy and power are discussed with emphasis on those methods which attempt to establish the accuracy or standards for such measurements. Devices to attenuate laser radiation are summarized. The principles and limitations of the methods are stressed rather than design details of the apparatus. It is found that standards for the measurement of laser power and energy are yet to be definitely established. Thus caution should be exercised in accepting stated accuracies for laser output measurements.

Far-infrared laser power measurements

Measurments of the peak and average output power of a 337-micron cyanide laser are reported. The tests served to indicate the usefulness at this high frequency of available oversize waveguide instrumentation-- a room-temperature average-power measurig bolometer, a liquid helium-cooled InSb detector-mixer and a double-prism attenuator.