How to adjust the laser intensity of laser confocal microscope
There are two adjustment factors of laser intensity: power control knob and Acousto-Optical Tunable Filter (AOTF).
1. Power control knob: generally set to 30% of the large value of *. With the increase of output, the life of laser will be shortened, and laser noise will also be generated. AOTF, PMT, etc. should be adjusted first to obtain good intensity.
2. Acousto-optic tunable filter: control the excitation light beam and intensity, and can turn on or off the laser at millisecond speed or adjust it to change between 0-100%. In this way, different laser beams can be used for each image point, and the required intensity can be selected.
Working principle: The Bragg diffraction effect of sound waves propagating in various media is utilized. When the RF signal with a certain frequency is input, AOTF diffracts the incident polychromatic light, and selects monochromatic light with an incoming wavelength. The wavelength of monochromatic light has a one-to-one correspondence with the RF frequency f, and the wavelength of the output can be changed quickly and randomly by tuning the electrical signal. AOTF can continuously adjust the laser intensity, and has the function of fast adjustment, realizing local stimulation and scanning, and fast wavelength switching (microsecond level). In laser confocal microscope, photomultiplier tube can not increase the laser intensity, but can adjust the photoelectric intensity after imaging, so the brightness of the image can be adjusted by adjusting the voltage of photomultiplier tube. In addition, the size of the pinhole affects the photon quantity and can also adjust the brightness of the image. The photomultiplier tube is a special vacuum tube which is extremely sensitive to ultraviolet light, visible light and near infrared light. It can increase the incoming weak optical signal to 108 times and make the optical signal be measured.
