Diode lasers are best absorbed in which of the following substances?

Diode lasers are particularly effective when used in conjunction with substances that have high absorbance at specific wavelengths of light emitted by the laser. Melanin and hemoglobin are known to strongly absorb light in the near-infrared spectrum, which is typically where diode lasers operate. This characteristic makes melanin and hemoglobin the most suitable choices for precise applications in therapies such as those targeting pigmented lesions or vascular conditions.

In contrast, while other substances listed may have their applications, they do not exhibit the same level of laser absorption as melanin and hemoglobin. For example, water absorbs light but is less specific and effective when targeting certain chromophores; it is often associated with thermal effects rather than specific therapies. Fluorescent dyes might be absorbed at different wavelengths, but they are not the primary targets for diode lasers. Calcium phosphate, commonly found in bone, does not have the strong absorbent characteristics for the wavelengths used by diode lasers, limiting its use in laser therapy contexts.

Therefore, the choice of melanin and hemoglobin highlights the importance of matching laser wavelengths with the optimal absorbent substances for effective treatment outcomes.