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KNOWLEDGE CENTER - HOW TO VARY THE INTENSITY OUTPUT FROM A LIGHT SOURCE |
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How to vary the intensity output from a light source. One of the most common problems arising from the use of a laser light source is the ability to vary the incoming light intensity. It is common for experimenters/researchers to encounter the situation whereby he/she would like to vary or control the intensity of the output. However, it is important to note that NO ATTEMPT should be made to manipulate the input voltage of the power supply to the laser. It would be best to consult your laser supplier before doing so. Mis-handling will either cause a failure and malfunction of the system or to a greater extend, hazard to the user. In this context, we proposed some of the low cost and yet efficient methods to enable you to do so. Method 1: Using ND (neutral density) filtersNeutral density filters, commonly known as ND filters, are used in the attenuation of light over a wide spectral range. They are often used in laser and photometer application, when it is necessary to control the intensity level of light in order to protect the measuring equipment or detecting devices such as a CCD camera from over saturation. Method 2: Using a polariser Ordinary light consists of both electric and magnetic waves travelling at right angle to each other. This is a light with random polarization, travelling at no specific direction. By placing a polarizing material, we are actually controlling it to pass through in one specific plane only, thereby linearly polarizing the light. Hence, if we place another polariser in conjunction with the first one, and by varying the transmission axis, it is possible to control the intensity of the transmitted light, thereby achieving attenuation of the light sources similar to using ND filter. Method 3: Expanding the beam This method employs a simple principle similar to those used by the beam expander. By knowing the power and the diameter of the emerging beam (look up the specification if you don’t), you could various the power and hence the intensity at a predetermine value. Employing the fact that when the beam expanded, its power is spread over the area it covered, hence giving the relationship that :
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