Patent ID: 8415627

Claim:
A fluorescence detection device using intensity-modulated laser light, which irradiates a measurement object with the laser light, receives fluorescence emitted from the measurement object to obtain a fluorescent signal, and determines fluorescence relaxation time from the fluorescent signal, the fluorescence detection device comprising: a laser light source unit emitting the intensity-modulated laser light with which the measurement object is to be irradiated; a light-receiving unit outputting the fluorescent signal of fluorescence emitted from the measurement object irradiated with intensity-modulated laser light; a signal generating unit generating a modulation signal having a predetermined frequency to modulate an intensity of the laser light emitted from the laser light source unit and generating, separately from the modulation signal, a first reference signal having a frequency different from that of the modulation signal in synchronization with the modulation signal; a signal processing unit comprising a first mixer that performs first mixing processing to mix the first reference signal and the fluorescent signal outputted from the light-receiving unit by irradiating the measurement object with the laser light whose intensity has been modulated using the modulation signal and a first low-pass filter that performs, on a mixed signal obtained by the first mixing processing, first low-pass filtering using a cut-off frequency lower than a sum frequency of a frequency of the modulation signal and a frequency of the first reference signal but higher than a difference frequency between the frequency of the modulation signal and the frequency of the first reference signal to output a fluorescent signal-based low-frequency signal; and a fluorescence detection unit that converts the fluorescent signal-based low-frequency signal into a digital signal and calculates a phase of the fluorescent signal relative to the modulation signal using a first signal component of the digital signal which corresponds to the difference frequency to determine a fluorescence relaxation time of the fluorescence emitted from the measurement object from the calculated phase.