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Linewidth and Depth of Field For a Structured Light Laser

Linewidth and Depth of Field For a Structured Light Laser

Mar 30, 2021

When choosing a structured light laser, there will be a lot of confusion about the depth of field of the line laser and the measurement range of the imaging system.


1. Definition of depth of field

As shown in the figure below, the laser has the smallest line width at the focal position (commonly used working distance position). Set to w0, as the working distance changes, the line width begins to increase, and the corresponding change distance is ±ZR, and ±ZR is the depth of field corresponding to the line width.


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2. Changes in depth of field

Take the 660nm wavelength laser as an example. The laser excited by a semiconductor diode is elliptically polarized light as shown in the figure below. In order to ensure the line width and depth of field, the elliptically polarized light is converted to linearly polarized light, so there are two corresponding types. One is the long axis type of linearly polarized light, which is conducive to large depth of field (corresponding to the dotted line), and the other is the short axis type of linearly polarized light, which is conducive to focusing (corresponding to the solid line)


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Therefore, it can be seen from the above figure that under the general light output power requirements, we all use the laser type corresponding to the dotted line. For example, if the working distance is 20cm, the corresponding line width is 200um, and the corresponding depth of field is about 70mm.


3. Choice of depth of field

The choice of depth of field is related to the line width. The line width itself is related to the illumination energy and the system resolution. Therefore, for the object to be measured with low reflectivity, a large line width (about 1mm) and a large depth of field (200mm) should be selected appropriately, but the effect of the type with high light intensity will be better.

We often more like the ultra-fine line width. In fact, thin line width is not the purpose. The purpose is to form a relatively obvious contrast distribution in the unit pixel of CCD. Therefore, the light energy density of the unit pixel is what we should be concerned when using it.


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ELITE’s Uniform Line Laser with “Powell Lens” and “Special Lens” providing uniform linewidth and intensity. Available wavelength 405nm ~ 850nm with output power up to 400mW. ELITE customized service provides high quality product and solutions for machine vision and measurement industry. If you have any further questions or specific requirements, please call us at

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