What Is a Shape Analysis Laser Microscope?
A Shape Analysis Laser Microscope is a microscope that uses a laser beam to measure the surface topography of an object.
Some microscopes have the same functionality but use a contact probe such as a cantilever, which touches the surface and may damage or scratch the sample. Shape analysis laser microscopes, on the other hand, utilize light reflection, allowing non-contact inspection.
Although the optical system is the same as that of a typical confocal laser microscope, many products are available that employ a high-speed MEMS scanner or resonant scanner to obtain three-dimensional information, thereby reducing scanning time.
Uses of Shape Analysis Laser Microscopes
Shape analysis laser microscopes are used to inspect various products and search for problems. In particular, they are often used for semiconductor components and printed circuit boards, because the components themselves are very small and have an elaborate surface structure, allowing non-contact, non-destructive inspection.
Using a problem-free product as a reference and superimposing it on the image of the inspected part allows rapid detection of problem areas. Also, because it is non-contact, it can be used for soft samples, and no special pre-treatment is required, so it is also used for inspecting food products.
Principle of Shape Analysis Laser Microscopes
The microscope acquires surface shape information by emitting a laser beam and detecting its reflected light.
1. 2D Shape
Since the intensity of light attenuates with the square of the distance, monitoring the intensity of the reflected light will reveal the distance to the surface. In this case, if light from an out-of-focus object is inserted, the increase or decrease in reflected light will be averaged out, reducing sensitivity.
To prevent this, the microscope employs confocal optics with pinholes in the conjugate focal plane to cut excess light from the non-focal plane. The distance information to the surface is thus accurately obtained as two-dimensional information by scanning the laser in the X- and Y- directions.
2. Three-Dimensional Shape
Furthermore, by scanning the objective lens in the Z direction, three-dimensional 3D shape analysis can be performed. The spatial resolution in the planar direction depends on the wavelength of the laser according to Abbe’s law, as in general optical microscopy.
Therefore, if there is no problem with the sample, a near-ultraviolet laser with a shorter wavelength, such as 405 nm, can be used for high-resolution measurement.
More Shape Analysis Laser Microscope Information
1. Measurement Procedure Using a Laser Microscope
There are three main categories of microscopes: optical microscopes, electron microscopes, and scanning probe microscopes. Laser microscopy is a type of optical microscope.
The procedure from laser irradiation to image display in a laser microscope consists of the following six steps:
- A laser is used as the light source.
- The laser passes through the objective lens and scans the object to be measured.
- Reflected light from the measurement object is once again incident on the objective lens.
- A half mirror changes the path of the reflected light toward the detector.
- A pinhole at the imaging position eliminates scattered light.
- The laser incident on the detector is displayed as a 3D image by image processing using an amplifier, etc.
2. Surface Roughness by Laser Microscopy
Surface roughness in laser microscopy is a measure of the unevenness of a part’s machined surface. Surface roughness is a cyclic shape consisting of a series of peaks and valleys of different heights, depths, and densities (spacing).
Surface roughness changes the feel and texture of a surface. The larger the surface roughness, the rougher the surface is to the touch, and the less light is reflected. On the other hand, a surface with a small surface roughness is smooth and reflects light intensely like a mirror.
Today, the texture and feel of a product are considered important, and roughness is an important indicator for quality control of appearance. Indicators of surface roughness include arithmetic mean roughness (Ra) using average values and maximum height (Rz) using the sum of peaks and valleys.