## Abstract

A new detection technique for photothermal deflection spectroscopy and photoacoustic deflection spectroscopy is presented. The technique uses a pair of matched multiple slits placed in the path of the probe beam and oriented to block the probe light from the detector in the absence of a deflection signal. Significant improvement in the signal-to-noise ratio and in the frequency bandwidth compared with those available with current techniques is demonstrated.

© 2005 Optical Society of America

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### Equations (9)

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(1)
$${\mathrm{\Phi}}_{\text{M}}=\mathrm{\eta}F{\mathrm{\Phi}}_{0},$$
(2)
$$F=\frac{2}{\mathrm{\pi}}{\mathit{\int}}_{\mathrm{\pi}/2}^{3\mathrm{\pi}/2}\frac{{sin}^{2}\mathrm{\beta}}{{\mathrm{\beta}}^{2}}d\mathrm{\beta},$$
(3)
$$\mathrm{\beta}=\frac{\mathrm{\pi}bsin\mathrm{\theta}}{\mathrm{\lambda}}\cong \frac{\mathrm{\pi}\text{b}\mathrm{\theta}}{\mathrm{\lambda}}.$$
(4)
$$\mathrm{\Delta}F=\frac{1}{\mathrm{\pi}}\left(-{\mathit{\int}}_{-\frac{3\mathrm{\pi}}{2}}^{-\frac{3\mathrm{\pi}}{2}+\mathrm{\Delta}\mathrm{\beta}}\frac{{sin}^{2}\mathrm{\beta}}{{\mathrm{\beta}}^{2}}\text{d}\mathrm{\beta}+{\mathit{\int}}_{-\frac{\mathrm{\pi}}{2}}^{-\frac{\mathrm{\pi}}{2}+\mathrm{\Delta}\mathrm{\beta}}\frac{{sin}^{2}\mathrm{\beta}}{{\mathrm{\beta}}^{2}}\text{d}\mathrm{\beta}-{\mathit{\int}}_{\frac{\mathrm{\pi}}{2}}^{\frac{\mathrm{\pi}}{2}+\mathrm{\Delta}\mathrm{\beta}}\frac{{sin}^{2}\mathrm{\beta}}{{\mathrm{\beta}}^{2}}\text{d}\mathrm{\beta}+{\mathit{\int}}_{\frac{3\mathrm{\pi}}{2}}^{\frac{3\mathrm{\pi}}{2}+\mathrm{\Delta}\mathrm{\beta}}\frac{{sin}^{2}\mathrm{\beta}}{{\mathrm{\beta}}^{2}}\text{d}\mathrm{\beta}\right),$$
(5)
$$\mathrm{\Delta}\mathrm{\beta}=\frac{\mathrm{\pi}b}{\mathrm{\lambda}}\mathrm{\phi}.$$
(6)
$${\left(\frac{S}{N}\right)}_{\text{CM}}\propto \sqrt{\frac{\mathrm{\eta}{\mathrm{\Phi}}_{0}}{F}}\mathrm{\Delta}F,$$
(7)
$$\mathrm{\eta}=\frac{2}{\mathrm{\pi}{a}^{2}}{\mathit{\int}}_{-\infty}^{\infty}{\mathit{\int}}_{-d}^{d}exp[-2({x}^{2}+{y}^{2})/{a}^{2}]H\left(cos\frac{2\mathrm{\pi}y}{\mathrm{\Delta}}\right)\text{d}y\text{d}x,$$
(8)
$$\mathrm{\Delta}s=\frac{2}{\mathrm{\pi}{a}^{2}}[{\mathit{\int}}_{-\infty}^{\infty}{\mathit{\int}}_{-\infty}^{0}exp[-2({x}^{2}+{(y+\mathrm{\delta})}^{2})/{a}^{2}]\text{d}y\text{d}x-{\mathit{\int}}_{-\infty}^{\infty}{\mathit{\int}}_{0}^{\infty}exp[-2({x}^{2}+{(y+\mathrm{\delta})}^{2})/{a}^{2}]\text{d}y\text{d}x].$$
(9)
$${\left(\frac{S}{N}\right)}_{\text{BC}}\propto \sqrt{{\mathrm{\Phi}}_{0}}\mathrm{\Delta}s.$$