Measurement of small absorption coefficients of weakly absorbing or trace gases in the atmosphere has been one of the most important applications of laser photoacoustic devices. Normally, the major factor limiting the sensitivity of these systems is the spurious signal produced by the heating of the cell windows, due to the partial absorption of the laser pump radiation. We present a simple photoacoustic configuration that eliminates the spurious window and external background signals and enhances the main (real) signal of IR gaseous photoacoustic systems, optimizing the signal-to-noise ratio.336549555