Energy and Power Density: A Key Factor in Lasers Studies.

Abstract

To the editor I read with interest, three articles in subject of laser studies published in JCDR in last few months. The authors in their researches used different types of lasers devices: Niranjani et al., (diode laser), Murthy et al., (CO2 laser), Kanumuru and Subbaiah (diode and Nd:YAG lasers) [1–3]. Unfortunately the authors have not presented in their researches a value of energy density (fluency) of lasers which is key factor to measure a dose of energy absorbed by treated tissues [Table/Fig-1]. [Table/Fig-1]: Comparison of studies Different types of lasers with same or different wavelength have been utilized in medical market, but the varied inbuilt technology in these devices provides divergent results in energy density (amount of light) which is absorbed by the tissue. The total energy delivered, divided by the area (energy per unit area) is called fluency or energy density. In a number of examples, fluency is the most important parameter for laser therapy [4]. Aside from energy density, a second important parameter in lasers measurement is a power density. The power density (irradiance) is a ratio of power (P) in Watt (W) to the cross section area (I=W/cm2). The importance of this will be clarified when we consider the interaction of laser beams with different materials [5]. Example: A pulsed laser emitting a beam with repetition rate f =1 pulse per second (1Hz), with energy of 50mJ (0.05J), for two diameters of a laser tip, the results in fluency (J/cm2) are divergent: 200μm tip, E=J/πr2, r=0.5d, r=0.01cm; 0.05J/3.14*0.012= 159.2J/cm2 per pulse 400 μm tip, E=J/πr2, r=0.5d, r=0.02cm; 0.05J/3.14*0.012= 39.8J/cm2 per pulse As the example showed that doubling of tip diameter implicates in 4 times energy density growth. It is very important in all studies that a data which can help to repeat each experiment by other researchers should be provided. Thus, all the studies should include the important parameters which allow comparing different kinds of lasers [4]. In Niranjani et al., Murthy et al., and Kanumuru and Subbaiah studies it is not possible to calculate and compare energy or power density [1–3]. In the author’s opinion, it is important that researchers and clinicians using lasers be educated in laser science. Without doubt, the principal knowledge of laser physics is unquestionably important to utilize lasers in good and safe manner.