Wavelength response of first type of film with sound?

GreenXenon wrote:

What wavelengths of light specifically affect the type of film used in
the first movie containing an variable-density optical audio track? I
am specifically interested in the chemical composition of the optical
audio track.

The first variable-density tracks were in the 1910s (such as Tigerstedt
and Tri-Ergon) so probably used orthochromatic film, sensitive to blue
and green.

From what I know, most of the more modern films are unaffected by red
light.

Just backward: the older films were not sensitive to red light.
Panchromatic film, which is sensitive to red, became common in
cinematography in the 1920s.

Of course in the standard studio equipment of early talkies, the
soundtrack recording was done on a different strip of film in a
different machine from the camera, so the color response of the film in
the audio recording machine didn't matter. You could even use
pre-orthochromatic film, which was sensitive mostly to blue wavelengths,
as long as your flickering light source had enough output in the blue to
properly expose the track.

Only in a portable camera which exposed both picture and sound on the
same negative would color sensitivity be an issue, and as far as I know
the cameras that did (RCA 16mm models from the mid-1930s are the first I
know of) used variable-area recording rather than variable-density.

I'm thinking of a theoretical device using analog audio recording on
VD optical tracks containing the oldest film chemical composition. The
source of light are multiple laser beams consisting of wavelengths
that could record the audio onto the film. Each beam has a different
wavelength. The beams are then mixed together to get a single beam of
all the necessary wavelengths. The beam then shines onto the film to
record the audio.

This is unnecessarily complicated. The film is black-and-white. As
long as the optical track gets enough light to expose it properly, of a
color to which it is sensitive, it doesn't care if the light is a mix of
wavelengths or just one wavelength. So with orthochromatic film you
could use a blue or green laser by itself, rather than worrying about
multiple sources and mixing beams.

In fact, there is an advantage to using a single wavelength, in that you
can use a simpler lens to focus the optical track without having to
correct for chromatic aberration.

-Neil Midkiff