Abstract: An apparatus and method for improved detection of a chiral property of a sample begins with a probe beam of light having a first modulation frequency ? and is further modulated with a second modulation frequency ?. A non-linear photo-detector, which may include multiple detector portions to form a balanced receiver, mixes the first modulation with the second modulation to analyze frequency components at inter-modulated sidebands, where the level of the inter-modulated sidebands are related to the chiroptical property of the sample. The inter-modulated sidebands may be the additive sidebands or the subtractive sidebands. A lock-in detector can be used to receive a signal output from the non-linear photo-detector and generate the modulation signals at the different modulating frequencies. Furthermore, the non-linear photo-detector may analyze a ratio of the inter-modulated sideband levels, such as (?+2?)/(?+?), to yield a signal that is linearly related to the chiral property of the sample.