How to adjust laser intensity of confocal laser microscope
1. Power control knob: Generally set to 30% of the maximum value. Increasing the output will shorten the lifespan of the laser and generate laser noise. AOTF should be adjusted first, PMT and other techniques are used to obtain optimal intensity.
2. Acousto optic tunable filter: controls the excitation light beam and intensity, and can turn on or off the laser or adjust it between 0-100% within milliseconds. This allows for the use of different laser beams for each image point and the selection of the required intensity.
Working principle: It utilizes the Bragg diffraction effect of sound waves propagating in various media on the incident Bragg diffraction in the propagation medium. When a certain frequency of RF signal is input, AOTF diffracts the incident polychromatic light and selects monochromatic light with the wavelength of the input. The wavelength of monochromatic light corresponds one-to-one with the RF frequency f. As long as the electrical signal is tuned, the output wavelength can be quickly and randomly changed. AOTF achieves continuous adjustment of laser intensity and has fast adjustment function, realizing local stimulation and scanning, fast wavelength switching (microsecond level). In laser confocal microscopy, photomultiplier tubes cannot increase the intensity of laser, but can adjust the intensity of post imaging light. Therefore, by adjusting the voltage of the photomultiplier tube, the brightness of the image can be adjusted. In addition, the size of the focal pinhole affects the photon quantity and can also adjust the brightness of the image. A photomultiplier tube is a special vacuum tube that is extremely sensitive to ultraviolet, visible, and near-infrared light. It can enhance the incoming weak light signal by 108 times, allowing the light signal to be measured.
