We describe a non-traditional optical power meter which measures radiation pressure to accurately determine a laser's optical power output. This approach traces its calibration of the optical watt to the kilogram. Our power meter is designed for high-accuracy and portability with the capability of multi-kilowatt measurements whose upper power limit is constrained only by the mirror quality. We provide detailed uncertainty evaluation and validate experimentally an average expanded relative uncertainty of 0.016 from 1 kW to 10 kW. Radiation pressure as a power measurement tool is unique to the extent that it does not rely on absorption of the light to produce a high-accuracy result. This permits fast measurements, simplifies power scalability, and allows high-accuracy measurements to be made during use of the laser for other applications.

We introduce a micromachined force scale for laser power measurement by means of radiation pressure sensing. With this technique, the measured laser light is not absorbed and can be utilized while being measured. We employ silicon micromachining technology to construct a miniature force scale, opening the potential to its use for fast in-line laser process monitoring. Here we describe the mechanical sensing principle and conversion to an electrical signal. We further outline an electrostatic force substitution process for nulling of the radiation pressure force on the sensor mirror. Finally, we look at the performance of a proof-of-concept device in open-loop operation (without the nulling electrostatic force) subjected to a modulated laser at 250 W and find its response time is less than 20 ms with noise floor dominated by electronics at 2.5 W/√Hz.

The advent of viral marketing in South Africa has been supply focused and retail operators did not realise the importance of including customers' views during the creation of viral marketing strategies. Failure of these stores to incorporate customers' views during the crafting of viral marketing strategies, leads to ineffective viral advertising campaigns, product boycott and decrease in sales. Given the constant change in consumer needs and expectations, an understanding of customers' opinions towards viral marketing strategies adopted by a retail store in Johannesburg, has become a remarkable strategy to gain a competitive advantage. For that reason, it is important for retail stores to understand their customers' perceptions of viral marketing strategies. Based on this background, the purpose of this study was twofold: i) to assess customers' perceptions of viral marketing strategies, and ii) investigate how viral marketing strategies influence customers' buying behavioural intentions. A descriptive case study approach was conducted. A quantitative methodology, through which a structured questionnaire was also used to collect data from a sample of at least 172 customers at outlets of a retail store in Johannesburg. SPSS was utilised to conduct descriptive and multivariate analyses including factor analysis, correlations, and regression analyses. Results indicated that customers had negative perceptions towards viral marketing strategies tested. In addition, all the four predictor variables (informativeness, entertainment, irritation and source credibility) were found to be positively correlated to customer buying behavioural intentions. Recommendations and gaps for further research are also presented within the context of viral marketing theory.

We present the first measurements of kilowatt laser power with an uncertainty less than 1%. These represent progress toward the most accurate measurements of laser power above 1 kW at 1070 nm wavelength and establish a more precise link between force metrology and laser power metrology. Radiation pressure, or photon momentum, is a relatively new method of non-destructively measuring laser power. We demonstrate how a multiple reflection optical system amplifies the pressure of a kilowatt class laser incoherently to improve the signal to noise ratio in a radiation pressure-based measurement. With 14 incoherent reflections of the laser, we measure a total uncertainty of 0.26% for an input power of 10 kW and 0.46% for an input power of 1 kW at the 95% confidence level. These measurements of absolute power are traceable to the SI kilogram and mark a state-of-the-art improvement in measurement precision by a factor of four.

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