In the context of the double-slit experiment, the wavelength of light does not change as it passes through the slits and forms an interference pattern on the screen. The interference pattern observed in the double-slit experiment is a result of the wave nature of light.
The double-slit experiment involves shining a beam of light through two closely spaced slits in an opaque barrier. Behind the barrier, a screen is placed to observe the light pattern that emerges. When a coherent light source, such as a laser, is used, light waves pass through both slits and create two coherent wavefronts that overlap on the screen. The overlapping waves interfere with each other constructively (peaks aligning with peaks) and destructively (peaks aligning with troughs), resulting in an interference pattern of bright and dark fringes on the screen.
The key point is that the interference pattern depends on the wavelength of the light. When monochromatic (single wavelength) light is used, such as laser light, a specific interference pattern corresponding to that wavelength is observed. Changing the wavelength of the light will result in a different interference pattern.
Regarding the mention of "over 3B wavelengths of light that can be detected now," I'm not sure what you mean by "3B." However, it's true that light covers a broad spectrum of wavelengths, ranging from radio waves with wavelengths measured in meters to gamma rays with wavelengths on the order of picometers. Each specific wavelength of light behaves differently in the double-slit experiment and exhibits different interference patterns.
The double-slit experiment is a fundamental demonstration of the wave-particle duality of light and other particles, where matter and energy can exhibit both wave-like and particle-like properties depending on the experimental setup. In the case of light, its wave nature is evident when observing interference patterns, while its particle nature is demonstrated through the behavior of photons in quantized interactions.