| 摘要 |
<p>A laser (12) is driven at a modulation frequency (f) by a frequency generator (14) to create a modulated beam (16) used to illuminate a sample. Light reflected from the sample is detected at a pre-selected frequency, such as the second harmonic of the illuminating frequency, to reveal information about the sample. A feedback path (30) is provided to suppress the component at the pre-selected frequency from the modulated beam (16).</p> |
