Various types of background signals appear when wavelength-modulated (WM) diode-laser light is frequency doubled. We present a theoretical analysis of such background signals in terms of a previously derived formalism for WM spectrometry that is based on a Fourier series. Explicit expressions for various <i>nf</i> harmonics of the background signals are derived. The analysis shows that 2<i>f</i> detection will be plagued by significant background signals when frequency-doubled WM diode-laser light is used. It also demonstrates that 4<i>f</i> and 6<i>f</i> detection will experience background signals but not, however, to the same extent as 2<i>f</i> detection. The analysis illustrates clearly how the various <i>nf</i> harmonics of the background signals depend on entities such as modulation amplitude, associated intensity modulation, dispersion of the frequency-doubling material, laser power, and detuning. The background signals can take both positive and negative values, depending on the relation between these entities. Guidelines for how to minimize these background signals are given.
© 2001 Optical Society of America
(190.2620) Nonlinear optics : Harmonic generation and mixing
(300.1030) Spectroscopy : Absorption
(300.6260) Spectroscopy : Spectroscopy, diode lasers
(300.6380) Spectroscopy : Spectroscopy, modulation
Pawel Kluczynski, Åsa M. Lindberg, and Ove Axner, "Background Signals in Wavelength-Modulation Spectrometry with Frequency-Doubled Diode-Laser Light. I. Theory," Appl. Opt. 40, 783-793 (2001)