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M 2 is useful because it reflects how well a collimated laser beam can be focused to a small spot, or how well a divergent laser source can be collimated. It is a better guide to beam quality than Gaussian appearance because there are many cases in which a beam can look Gaussian, yet have an M 2 value far from unity. [1]
The square metre (international spelling as used by the International Bureau of Weights and Measures) or square meter (American spelling) is the unit of area in the International System of Units (SI) with symbol m 2. [1]
There are several ways to define the width of a beam. When measuring the beam parameter product and M 2, one uses the D4σ or "second moment" width of the beam to determine both the radius of the beam's waist and the divergence in the far field.
In physiology and medicine, the body surface area (BSA) is the measured or calculated surface area of a human body.For many clinical purposes, BSA is a better indicator of metabolic mass than body weight because it is less affected by abnormal adipose mass.
The body mass index is expressed in units of kilograms per square meter, though the area figure is nominal, being the square of the height. The total electron content in the ionosphere is a quantity of type columnar number density. Snow water equivalent is a quantity of type columnar mass density.
The candela per square metre (symbol: cd/m 2) is the unit of luminance in the International System of Units (SI). The unit is based on the candela, the SI unit of luminous intensity, and the square metre, the SI unit of area.
The cardiac index (CI) is a hemodynamic measure that represents the cardiac output (CO) of an individual divided by their body surface area (BSA), expressed in liters per minute per square meter (L/min/m²). This parameter provides a more accurate assessment of heart function relative to the size of the individual, as opposed to absolute ...
The heat transfer coefficient has SI units in watts per square meter per kelvin (W/(m 2 K)). The overall heat transfer rate for combined modes is usually expressed in terms of an overall conductance or heat transfer coefficient, U. In that case, the heat transfer rate is: ˙ = where (in SI units):