Laser Energy Measurements Research Articles

Dynamics and correlated performance of a photo-triggered discharge-pumped HF laser using SF 6 with hydrogen or ethane

, has been performed in Ne/SF6/H2 and Ne/SF6/C2H6 mixtures. Parameters involved have been the storage line capacitance and the circuit inductance, the capacitors charging voltage, the RH-molecule type and partial pressure, and the X-ray dose for the preionization. High laser performance has been achieved with C2H6: an output energy up to 3 J corresponding to a specific energy of 9.6 J/l at an efficiency of 4.7%, which strengthens the advantage of the photo-triggering technique to energize high-power HF lasers. However the optimum performance achieved with H2, 5.75 J/l and 3.5%, are lower. It is shown, through a time-resolved study of the electrical discharge and spatial dynamics correlated to laser power and energy measurements, that discharge instabilities are responsible for the poor laser performance of the mixture with H2. These instabilities, which lead to arc development, are characteristics of the discharge in Ne/SF6. It is demonstrated for the first time that addition of a heavy hydrocarbon, such as C2H6, to that mixture induces the discharge stabilization so that the laser emission arises in a homogeneous active medium. This effect allows us to achieve better laser performance than with H2.

An intelligent maximum permissible exposure meter for safety assessments of laser radiation

There is frequently a need to make laser power or energy density measurements when determining whether radiation from a laser system exceeds the Maximum Permissible Exposure (MPE) as defined in BS EN 60825. This can be achieved using standard commercially available laser power or energy measurement equipment, but some of these have shortcomings when used in this application. Calculations must be performed by the user to compare the measured value to the MPE. The measurement and calculation procedure appears complex to the nonexpert who may be performing the assessment. A novel approach is described which uses purpose designed hardware and software to simplify the process. The hardware is optimized for measuring the relatively low powers associated with MPEs. The software runs on a Psion Series 3a palmtop computer. This reduces the cost and size of the system yet allows graphical and numerical presentation of data. Data output to other software running on PCs is also possible, enabling the instrument to be used as part of a quality system. Throughout the measurement process the opportunity for user error has been minimized by the hardware and software design.

Laser measurements in the infrared

Lasers that operate in the mid-infrared (∼1–20 μm) have many applications, ranging from molecular spectroscopy to monitoring pollution in the atmosphere. However, it is difficult to design systems for making accurate measurements of laser power, energy and beam profile in the mid-infrared because several problems arise that do not occur in the visible and near-infrared regions. These are summarized below and will be discussed in more detail later:

Investigation of nonlinearity in conversion characteristics op fine-wire bolometric gauges for measurement of laser radiation intensity and energy

Investigation of nonlinearity in conversion characteristics op fine-wire bolometric gauges for measurement of laser radiation intensity and energy

レーザ出力の測定

レーザ出力の測定

Output and discharge characteristics of an X-ray preionized XeCl laser with a large active volume.

The output and discharge characteristics of an x-ray preionized Xe Cl laser with a pulse forming line (PFL), a rail-gap switch (RGS) and a pulse transmission line (PTL) in the excitation circuit are described in detail. It is found that the relatively large inductance of the RGS leads to the efficient energy deposition into the discharge plasmas when the RGS is placed between the PFL and the PTL. The laser system with a low output impedance of 0.26Ω has produced the maximum laser energy of 50 J in an 85-ns pulse (FWHM). The highest electrical efficiency obtained is 3.1%. The discharge stability is also discussed, based on the measurements of laser pulse-shape, laser energy and voltage on the laser electrode.

Analysis of metrological characteristics of specialized digital meter for laser-energy measurement means

nominal input signal of amplifier A2. Then s ! 0.5.10-3%. The drift of the Input current of the amplifier and the leakage current of the commutator is 0.5.10 -~~ A/~ which results in additional temperature error. When the temperature varies by 10~ the error ATt ! 0.5. I0-~%. Errors of Input Amplifier Af. The relative errors due to instability of the feedback resistances of amplifier A2 may be ignored, since in the ADC there are no limitations of the stability of the transmission coefficient of amplifier A2, because the measured voltage U x and the reference voltage Uo are fed to the same input. It is known that the gain Kfb affects the attenuation factor of the in-phase signal Mip

Efficient XeF(C→A) laser oscillation using electron-beam excitation

Significantly improved XeF(C→A) laser energy density and efficiency have been obtained using electron-beam excited Ar-Xe gas mixtures at pressures up to 10 atm which contain both NF3 and F2. Maximum blue-green laser pulse energy density in excess of 1.0 J/liter was obtained, corresponding to an intrinsic electrical-optical energy conversion efficiency estimated to be in the 0.5%–1.0% range. Comprehensive, time-resolved absolute measurements of XeF(C→A) fluorescence, laser energy, and gain were carried out for a wide variety of experimental conditions. Analysis of these data has resulted in identification of the dominant transient absorbing species in the laser medium. For the laser mixtures investigated in this work, the primary blue/green absorption processes have been identified as photoionization of the 4p, 3d, and higher lying states of Ar, and of the Xe 6p and 5d states, and photodissociation of Ar2(3∑+u) and Ar+3.

Digital measuring instruments for working standards and standard means of measurement of laser mean power and energy

Digital measuring instruments for working standards and standard means of measurement of laser mean power and energy

High accuracy laser power measurements: a scale comparison

Measurement scales for laser power and energy measurements using the C-series calorimeters, an electrically calibrated pyroelectric null radiometer, and a commercially available self-calibrating twin calorimeter system were compared at the 3-mW and 30-mW levels at 488 nm and 647.1 nm. Results show agreement in absolute measurements by these devices to within estimated uncertainties. A similar comparison at the 9-mW level of the argon UV laser lines (351.1 nm and 363.8 nm) showed agreement between measurements made by the C-series calorimeter and the electrically calibrated pyroelectric radiometer to within measurement uncertainties. A discrepancy of about 10% between these and the twin calorimeter measurements may be due to an uncorrected window transmission error in the latter.

Quantitative energy extraction measurements in a photoionization-stabilized self-sustained XeF laser

Detailed time-correlated gain, flourescence, and laser energy measurements were used to obtain quantitative data on energy extraction efficiencies for a photoionization-stabilized self-sustained XeF laser. A current pulse of 25 ns full width at half-maximum produced an 80-cm3 XeF plasma in NF3 : Xe : He gas mixtures with a maximum output energy of 80 mJ. The results show that the maximum small-signal gain and the maximum specific output energy is proportional to the NF3 content of the gas mixture. This suggests that there is an optimum fractional utilization of the NF3 molecules in the discharge. Under high-gain conditions, 30–40% of the energy stored in XeF* can be extracted in a gain-switched pulse. The output energy represents less than 1% of the input energy.

Evaluating the inequivalence and a computational simplification for the NBS laser energy standards

A model with two time constants is used to estimate the inequivalence in response between a laser energy pulse and an electrical energy pulse put into a calorimeter of the C series type. The results are as follows: the calorimeter labeled C41 showed a 0.15% inequivalence and the calorimeter labeled C46 showed none. We also find that the complicated model currently used to get the corrected temperature rise of a measurement can be replaced by a simpler four-data-point method with no significant loss in accuracy. This simplification means we can substitute a microprocessor for a large computer to get the corrected temperature rise in an electrical calibration or laser energy measurement.

Current Status of NBS Low-Power Laser Energy Measurement

A set of four electrically calibrated calorimeters is currently in use at the Boulder Laboratories of the National Bureau of Standards to calibrate and test devices for measuring average laser power in the range from 100 μW to 1 W and energies in the range 0.03 to 10 J. Laser sources used with these calorimeters are argon, krypton, helium-neon and neodymium-doped YAG, all CW, and pulsed YAG with pulse energies about 0.1 J and pulsewidths of about 200 μs and 30 ns. The calorimeters have been intercompared as a check on systematic errors. The national standard is taken as the average for three of the calorimeters of the current C4 design, because these were designed to permit better measurements of the absorptance and window transmittance. Deviations from the group average are -0.12, -0.01, and +0.13 percent. The earlier standard C3-1 differs from the group average by +0.21 percent.

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.

A Reference Calorimeter for Laser Energy Measurements.

Principles and detailed procedures are described for measuring laser energy and power in terms of electrical energy based on voltage, resistance, and frequency standards. The construction of a small isoperibol calorimeter used for the measurements is described. The calorimeter will accommodate 0.01 to 20 J and 4 × 10-5 to 1 W cw and is limited to a maximum pulse intensity of 0.1 J/cm2. The standard deviation of comparison measurements using two calorimeters and a beam splitter is 0.08 percent when the smaller energy input is not less than 0.3 J. The estimated limits of systematic error for one calorimeter are ± 1.0 percent of the laser energy measured by the calorimeter.

Accurate digital measurement of pulsed laser energy

An energy measuring system has been developed using a planar vacuum photodiode as detector with capacitative integration of the photocurrent and subsequent display on a digital voltmeter. The great advantages of this system are that (i) it is small in size and weight at the optical end, (ii) it produces an instantaneous readout, (iii) the readout is digitally expressed directly in millijoules, (iv) the system is independent of ambient light level, (v) simultaneous measurement of power is available and (vi) the operation is automatic. Comparison with a standard calorimeter shows that the system has a consistency of better than 1%.

Measurement of Laser Energy of Linear Components of Polarization at 1.060 μ

A double reflecting plate calorimeter [Rev. Sci. Instrum. 41, 1479 (1970)] was used to evaluate the energy components of a pulsed 1.060 μ neodymium laser light beam entering the calorimeter polarized parallel (EH) and perpendicular (EV) to a horizontal plane. The relationship between these components varied from EH = 0.94 EV to EH = 1.25 EV. Estimated error of EH and EV is 2.3%. As a check on the accuracy of polarization component measurements at 1.060 μ, an intercomparison of data was made between this calorimeter and an NBS liquid cell calorimeter. The agreement was about 0.2%.

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.