聚焦光斑大小

聚焦光斑大小主要取决于透镜焦距长短(对特定激光, 发散角已定). 光斑大小可估计为 "

焦距 X 发散角". 当然, 焦距过短, 相对孔径大, 象差的影响也需要考虑.

焦距和聚焦镜片

一束直径固定的光是由一片镜片来获得一个较小的光点，如图一所示，假如焦点的直径d0 是一个含有86%聚焦能量的直径，焦点的大小取决于

d0=2fλ/D

这里的f是聚焦镜片的焦距。D是入射光束的直径，也就是波长.

图一：高斯光束的聚焦图

如果光的总发散角度θ已知，焦点的直径则为

d0=f . υ

很明显如果焦点越小，则光的发散角度就越小。为了取得一个较小的焦点，我们利用扩束镜来减小应用过程中光束的发散角度。

当光束从镜片中心穿过然后发散出去，需要界定光的焦点的深度。一般来说，它是由√2d0 点之间的距离或2倍瑞利范围决定的。它可以表示成：

?f=2ZR≈2πλF 2或者?f=2f 2θ/D

在大多数的扫描结果里，焦斑的尺寸大小通常是以平均值的形式给出的。

这里的F是聚焦镜片的f值，它是这样定义的：

F=f/D

由以上公式可以得出结论，一片有较长焦距的镜片相比一片焦距较短的镜片而言，焦距较长的镜片能够得到一个比较深而大的焦点，所以应当根据实际运用的需要来选择焦距合适的镜片。

Focusing: Objectives and vario SCAN s

Whereas objectives are mounted at the scan system's beam exit, vario SCAN focusing units are installed to precede the scan system's deflection mirrors. The focusing optic's type and focal length (or conjugate) are selected to meet application-specific requirements for wavelength, laser power, spot size, image field size and working distance.

F-Theta objectives achieve flat image fields and offer high precision along with

freedom from dynamics limitations. Short-focal-length F-Theta objectives are

capable of short working distances, which allows creation of very

compactly-dimensioned systems. SCANLAB offers an extensive range of F-Theta and

flat field objectives (including telecentric objectives). Customer-specified

components are also possible.

Alternatively, vario SCAN focusing units can focus onto a

flat image field. An RTC? board adjusts the vario SCAN's

focal length for each position of the deflection mirrors such

that the laser focus always remains in the desired plane.

The same process can be applied to position the focus

along the beam axis, thus enabling true 3D laser

processing of materials. SCANLAB offers vario SCAN optics

for all typical wavelengths.

Depending on the optical configuration, processing within

large image fields and at high laser powers is possible. And

large working volumes are achievable by combining a

vario SCAN unit with an F-Theta objective.