The influence of environmental vibration sources is easy to become a problem when precise experiments or measurements are carried out in laboratories. Some experiments may not be possible due to the influence of slight vibration. For example, many laser applications require several microns of beam waist; if the position of the spot is critical to the system performance, the vibration of several microns of amplitude will also cause the failure of the experiment. Because the wavelength of visible light is in the order of sub-micron, even the amplitude of sub-micron can make the experiment based on interferometry (including holography) impossible in the presence of vibration. Similar stability is required for optical/mechanical processing or detection of semiconductor wafers. In addition to the influence of external vibration sources, if displacement or vibration components are used in experiments, they are often isolated from other vibration sensitive components.
Optical platform is to solve this problem. It uses active or passive vibration isolation measures to isolate vibration and provide a level and stable platform. Ensure that the experiment or measurement is free from vibration factors.
In order to achieve the desired effect, the optical platform must satisfy several conditions. First of all, it must have a rigid table, which can fix the experimental instrument stably for a long time. Secondly, it has no inherent resonance, and can effectively suppress any vibration generated by the motor or the moving part in the experiment, and can isolate the influence of environmental vibration on the experimental device.
Under the above ideas, a variety of optical platforms and optical breadboard designs have been produced. In general, the optical platform has a rigid flat but not too heavy upper surface, and then air springs are used to prevent the interference of ambient vibration. Previously, the mesa was often made of granite, cement, wood, steel and other composite materials to improve performance while the weight was acceptable. Obviously, these materials have their own advantages and disadvantages. Nowadays, it is generally believed that honeycomb platform with metal honeycomb structure is the best material for optical platform and optical breadboard structure.
Indicators and Detection of Optical Platform
How to identify the quality of the optical platform and select the suitable optical platform, the following provide some general indicators and detection methods.
1. Inspection of appearance
The appearance of the optical platform should be smooth and beautiful, and there should be no sharp angle and edge affecting safety in all parts. More importantly, it is important to check whether the chamfer of the orifice is uniform (the screw hole should be turned into the vertical platform surface), and whether the four sides and chamfer are flat and consistent. If the processing accuracy is not good, the chamfer size of the hole will be inconsistent or the chamfer around the table surface will not be smooth.
2. Natural frequency (<2Hz)
Natural frequencies are also called natural frequencies and natural frequencies. Only when the ratio of environmental disturbance force frequencies (f) to the natural frequencies of optical platforms (fo) is f/fo>2, can the system isolate vibration. Therefore, the lower the natural frequency of the optical platform, the better the vibration isolation effect.
The detection of this index usually uses vibration spectrum analyzer and portable vibration analyzer for multi-point measurement. If the supplier does not have the instrument for measurement, it can also use the following methods: press down (or push sideways) the platform by hand, then release it quickly, and make it vibrate up and down (or swing up and down, front and back) by a large margin. If it is reciprocating once in a second, it will be 1Hz, and then it will be 2Hz. PUSH. The natural frequency of the optical platform must be roughly measured.
3. Planarity (<0.05mm/m2)
The smaller the index is, the easier it is to adjust the light path. Generally, flatness is required to be less than 0.05 mm/m2. The detection methods include photoelectric autocollimator, optical flatness tester, level tester, laser flatness tester and so on. The flatness of the optical platform installed in the laboratory is generally measured by photoelectric collimator and optical flatness checker, which is calculated.
4. Surface dense texture and roughness (Ra < 0.8um)
The significance of this index is to ensure that the optical platform has a smooth but non-reflective working surface. Good surface roughness is conducive to the protection of experimental instruments. Optical platforms are generally required to be manufactured below Ra < 0.8 um. The roughness can be measured by contrast sample visual measurement and roughness tester, and if it is detected in the field, the roughness tester can be used. The instrument has the advantages of portable, direct reading data and high accuracy.
5. Repeated positioning accuracy (+0.10mm)
The significance of this index lies in ensuring the level of optical platform in dynamic conditions to facilitate users'high-speed optical path. The detection method is to fix the percentile meter (accuracy 0.02mm) on a solid object, the head of the meter is on the table, and then load or unload repeatedly on the optical platform workbench. After stabilization, the reading is qualified within the range of positive and negative 0.10mm.
6. Amplitude of working table (So < 2 um)
In normal use environment, in order to ensure the accuracy of the instrument, the optical platform must provide the lowest possible amplitude. At the same time, the vibration isolation performance of the system can be reflected by comparing the amplitude indices of the mesa and the ground. If the amplitude of the platform is less than that of the ground, the platform is vibration-isolating, otherwise it is not vibration-isolating or vibration amplification. The detection of amplitude index is similar to that of natural frequency.
Several Notices for Purchasing Optical Platform
1. With the continuous improvement of the quality requirements of optical platforms by many research institutes and the continuous improvement of products by manufacturers, there are many types of optical platforms and their quality is uneven. So before purchasing optical platforms, enterprises should first have a certain understanding. Secondly, the material of the optical platform, processing accuracy, vibration isolation effect, the rationality of the product as a whole, whether the surface of the platform is fine or not, and the technology of surface treatment, etc.
2. We should not attach too much importance to one or two parameters of the product. We should understand the whole optical platform and test it. For example, the important parameters of optical platform, such as flatness, platform roughness, natural frequency, amplitude, working pressure and maximum load, should be understood and tested in detail. In this way, we can choose the optical platform we want to buy according to some important parameters.
3. When purchasing optical platforms, we should compare the prices more and make sure that we have a good idea. It is not the cheaper the better. It is necessary to choose an optical platform that meets the demand. The key is to have a high cost-effective optical platform.