Seeing nonspectral colors with single wavelength stimulation in two-photon vision

Area of Science:

• Optics and Photonics
• Human Visual Perception
• Laser Physics

Background:

• Pulsed near-infrared (NIR) lasers can elicit color perception via two-photon (2P) absorption, effectively halving the perceived wavelength.
• At high intensities, single-photon (1P) absorption also contributes to color perception beyond 700 nm.
• The interplay between 1P and 2P absorption dictates the overall color experience in the NIR spectrum.

Purpose of the Study:

• To investigate the interaction between 1P and 2P absorption in the NIR spectrum.
• To explore the range of colors producible by manipulating laser parameters.
• To understand how laser power and repetition frequency influence perceived color.

Main Methods:

• Color matching experiments were conducted using seven pulsed laser wavelengths ranging from 730 nm to 920 nm.
• The study utilized a nanosecond-pulsed laser system, adjusting power and repetition frequency.
• Observer color perception was systematically recorded for each experimental condition.

Main Results:

• A spectrum of perceived colors was observed, from red at shorter wavelengths to blue at longer wavelengths.
• Nonspectral colors, specifically shades of purple, were successfully generated using single NIR wavelengths.
• Modifiable hue shifts were detected between 850 nm and 920 nm, with peak sensitivity to changes between 880 nm and 900 nm.

Conclusions:

• Single NIR wavelengths can stimulate the perception of nonspectral colors like purple.
• Laser power and repetition frequency are critical parameters for tuning perceived color hue in the NIR.
• This research expands the understanding of color vision mechanisms involving multi-photon absorption processes.