An apparatus for measuring a presence of predetermined material within a sample, comprises signal generation circuitry for generating a first signal having an applied first orbital angular momentum signature and applying the first signal to the sample. A detector receives the first signal after the first signal passes through the sample and determines the presence of the predetermined material within the sample based on a detected second orbital angular momentum signature within the first signal received from the sample. The detector provides an output of an indication of the presence of the predetermined material responsive to the determination.