A method for determining a calibration status of an optical particle analyzer independent of particles, the method comprising the steps of: providing an optical particle analyzer including: a source of electromagnetic radiation (EMR) for generating a beam of said EMR; a chamber for containing a sample medium and for receiving said beam of EMR; an optical assembly in optical communication with the source of EMR for directing the beam of EMR from the source to the chamber; a detector for detecting scattered radiation from said beam of EMR an optical collection system for directing said scattered radiation from the beam of EMR from the chamber and to the detector; modulating a power applied to the source of EMR; in response to the modulating step, inducing a detector signal waveform having a low frequency time domain; analyzing the detector signal waveform to determine a value of at least one diagnostic parameter associated with one or more of the source of EMR, the optical assembly, the chamber, the detector, and the optical collection system; determining the calibration status of the optical particle analyzer based on the one or more determined values of the at least one diagnostic parameter; wherein for one or more particles present in the optical particle analyzer and in response to the step of modulating the power applied to the source of EMR a particle detection signal is generated having a middle frequency time domain that is higher than the low frequency time domain, thereby avoiding unwanted interference between the low frequency time domain of the detector signal and the middle frequency time domain of the particle detection signal; thereby determining the calibration status of an optical particle analyzer independent of particles. providing an optical particle analyzer including: a source of electromagnetic radiation (EMR) for generating a beam of said EMR; a chamber for containing a sample medium and for receiving said beam of EMR; an optical assembly in optical communication with the source of EMR for directing the beam of EMR from the source to the chamber; a detector for detecting scattered radiation from said beam of EMR an optical collection system for directing said scattered radiation from the beam of EMR from the chamber and to the detector; modulating a power applied to the source of EMR; a source of electromagnetic radiation (EMR) for generating a beam of said EMR; a chamber for containing a sample medium and for receiving said beam of EMR; an optical assembly in optical communication with the source of EMR for directing the beam of EMR from the source to the chamber; a detector for detecting scattered radiation from said beam of EMR an optical collection system for directing said scattered radiation from the beam of EMR from the chamber and to the detector; modulating a power applied to the source of EMR; in response to the modulating step, inducing a detector signal waveform having a low frequency time domain; analyzing the detector signal waveform to determine a value of at least one diagnostic parameter associated with one or more of the source of EMR, the optical assembly, the chamber, the detector, and the optical collection system; determining the calibration status of the optical particle analyzer based on the one or more determined values of the at least one diagnostic parameter; wherein for one or more particles present in the optical particle analyzer and in response to the step of modulating the power applied to the source of EMR a particle detection signal is generated having a middle frequency time domain that is higher than the low frequency time domain, thereby avoiding unwanted interference between the low frequency time domain of the detector signal and the middle frequency time domain of the particle detection signal; thereby determining the calibration status of an optical particle analyzer independent of particles. <EOS>