The short-wavelength 755 nm laser is best known for which combination of properties?

• A. High frequency
• B. High intensity
• C. Light skin
• D. High frequency, high intensity, and light skin

Answer: (D)

The wavelength determines how strongly the laser’s energy is absorbed by melanin in the skin and hair, and how deeply the light penetrates. A 755 nm Alexandrite laser is a short-wavelength option, which means it is absorbed very well by melanin in hair fibers. This allows delivering high energy per pulse (high intensity) to the hair follicle with strong selective targeting, and modern machines can deliver pulses rapidly (high repetition rate or high frequency) to cover larger areas quickly. However, because skin also contains melanin that can absorb energy at this wavelength, it is most safely used on lighter skin types where epidermal melanin is lower. That combination—high energy pulses, fast pulse delivery, and suitability for lighter skin—describes what this wavelength is best known for.