755nm Bandpass Filter

Context: Modern "blended" laser systems (like the Thunder or Splendor X) that fire both 755 nm (Alexandrite) and 1064 nm (Nd:YAG) simultaneously to treat mixed hair/skin types.

Usage of Filter: The filter is used as a Dichroic Beam Combiner.

Function: The optical element is coated to have a "Pass Band" at 755 nm and a "Reflection Band" at 1064 nm. It sits at a 45-degree angle where the two laser paths intersect. It allows the 755 nm beam to pass straight through while reflecting the 1064 nm beam into the exact same path.

Result: This achieves co-linear mixed emission. Both wavelengths exit the same fiber optic cable and hit the skin at the same spot, allowing the doctor to attack both the hair shaft (755 nm) and the blood supply (1064 nm) in a single pulse.

Context: Safety gear for operators of Alexandrite lasers. Since 755 nm is barely visible (deep red) but extremely high energy, it is dangerous to the retina.

Usage of Filter: The filter is used as a Notch Absorber (Band-Stop) in the safety glasses.

Function: It uses specific dyes (often rare-earth based) molded into the polycarbonate lens to create a "brick wall" absorption specifically at 755 nm (OD 7+), while leaving the rest of the visible spectrum (400–700 nm) relatively clear.

Result: This achieves high Visible Light Transmission (VLT) with safety. Unlike older "dark green" goggles that made it hard to see veins or skin reaction, these filters allow the doctor to clearly see the patient's skin tone and redness (erythema) while being completely protected from the laser flash.

Context: Picosecond laser systems for tattoo removal (e.g., PicoSure).

Usage of Filter: The filter is used as a Pump Separator.

Function: In systems where the 755 nm beam is used to "pump" a crystal to generate other wavelengths (like red or yellow for specific ink colors), a filter is placed after the crystal. It blocks the residual 755 nm pump light from mixing with the new converted wavelength.

Result: This achieves color purity. If the 755 nm light leaked through, it could cause unwanted blistering on darker skin (which absorbs 755 nm strongly) when the target was actually a specific ink color that required a different wavelength.