| CPC G02B 27/58 (2013.01) [G01N 21/21 (2013.01); G01N 21/6458 (2013.01); G02B 21/0048 (2013.01); G02B 21/0076 (2013.01); G02B 27/141 (2013.01); G02B 27/286 (2013.01); G01N 2021/6463 (2013.01); G01N 2201/06113 (2013.01); G01N 2201/0683 (2013.01); G01N 2201/105 (2013.01)] | 5 Claims |
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1. A device for removing background noise based on frequency-domain modulation, comprising: a laser device and a sample stage carrying a sample to be measured, a space between the laser device and the sample stage sequentially arranged with:
a glan prism configured to change polarization states of a laser beam emitted by the laser device to obtain line-polarized light, the laser beam including a high-power laser and a low-power laser;
an electro-optic modulator configured to modulate intensities of two beams of the line-polarized light corresponding to the high-power laser and the low-power laser to obtain two beams of line-polarized light with different preset frequencies;
a 0˜2π vortex phase plate configured to perform phase modulation of the high-power laser;
a quarter-wave plate configured to change polarization states of the two beams of line-polarized light to obtain two beams of right-handed circularly polarized light;
a dichroic mirror configured to combine the low-power laser and the high-power laser after phase modulation into a single beam;
a galvanometer scanner configured to deflect an optical path of right-handed circularly polarized light; a scanning lens and a field lens configured to focus and collimate a light beam emitted from the galvanometer scanner;
a microscope objective configured to project a light beam emitted from the field lens onto the sample to be measured to make the high-power laser after phase modulation converge into a hollow spot on the sample to be measured and make the low-power laser converge into a solid spot on the sample to be measured;
a detection module configured to collect signal light emitted by the sample to be measured;
a lock-in amplifier configured to demodulate the received signal light at a specific frequency to obtain an image at a corresponding scanning position;
a controller configured to control the galvanometer scanner; and
a signal generator configured to control a frequency of the electro-optic modulator and a frequency of the lock-in amplifier; wherein
a single-mode fiber and a collimating lens are arranged in sequence between the laser device and the glan prism and are configured to filter and collimate the laser beam;
the 0˜2π vortex phase plate has a variable modulation function f(p,φ)=φ, where p donates a distance of a point on a beam from an optical axis, and φ donates an angle of a polar coordinate vector of a position within a cross-section perpendicular to an optical axis of the beam from x-axis; and
the detection module includes a beam splitter, a bandpass filter, a detector, a collection lens, and a spatial filter, wherein
the beam splitter is arranged between the 0˜2π vortex phase plate and the galvanometer scanner,
the bandpass filter is configured to filter out stray light of a signal beam emitted from the beam splitter,
the collection lens is configured to focus the filtered signal beam onto the detector,
the spatial filter is disposed at a focal plane of the collection lens, and is configured to spatially filter the filtered signal beam, and
the detector is configured to detect a light intensity signal of the filtered signal beam.
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