An optical detection system includes a sample carrier receiving region that receives a sample carrier carrying a sample. The system further includes a source that emits an excitation signal having a wavelength within a predetermined wavelength range. The excitation signal illuminates the sample carrier. A first sub-portion of the excitation signal is absorbed by the sample, which emits characteristic radiation in response thereto. A second sub-portion of the excitation signal traverses the sample carrier. The system further includes a detector that detects the characteristic radiation. The system further includes an absorber that absorbs the excitation signal traversing the sample carrier without being absorbed by the sample or sample carrier. The absorber absorbs at least 95% of the excitation signal traversing the sample carrier.