The phase difference at the beam splitter of a LIGO-like interferometer is given by $$ \Delta \phi \simeq \frac{4\pi}{\lambda} h L\ , $$ where $h$ is the gravitational wave strain (assuming a polarisation aligned with the detector arms), $L$ is the effective arm length (increased by a large factor in the Fabry-Perot cavities) and $\lambda$ is the interferometer laser wavelength, and assuming the frequency is low enough to not be affected by the response roll-off of the Fabry-Perot cavities.

Why then does LIGO use an IR laser ($\lambda = 1064$ nm), rather than something with shorter wavelength that would produce a larger (and more detectable) phase difference?

I would think this probably has to do with how absorptive the optics are at different wavelengths, but cannot find definitive statements about this other than that the fused silica substrate of the mirrors is "transparent" at both visible and IR wavelengths.

The phase difference at the beam splitter of a LIGO-like interferometer is given by $$ \Delta \phi \simeq \frac{4\pi}{\lambda} h L\ , $$ where $h$ is the gravitational wave strain (assuming a polarisation aligned with the detector arms), $L$ is the effective arm length (increased by a large factor in the Fabry-Perot cavities) and $\lambda$ is the interferometer laser wavelength, and assuming the frequency is low enough to not be affected by the response roll-off of the Fabry-Perot cavities.

Why then does LIGO use an IR laser ($\lambda = 1064$ nm), rather than something with shorter wavelength that would produce a larger (and more detectable) phase difference?

I would think this probably has to do with how absorptive the optics are at different wavelengths, but cannot find definitive statements about this other than that the fused silica substrate of the mirrors is "transparent" at both visible and IR wavelengths.

The phase difference at the beam splitter of a LIGO-like interferometer is given by $$ \Delta \phi \simeq \frac{4\pi}{\lambda} h L\ , $$ where $h$ is the gravitational wave strain (assuming a polarisation aligned with the detector arms), $L$ is the effective arm length (increased by a large factor in the Fabry-Perot cavities) and $\lambda$ is the interferometer laser wavelength, and assuming the frequency is low enough to not be affected by the response roll-off of the Fabry-Perot cavities.

Why then does LIGO use an IR laser ($\lambda = 1064$ nm), rather than something with shorter wavelength that would produce a larger (and more detectable) phase difference?

I would think this probably has to do with how absorptive the optics are at different wavelengths, but cannot find definitive statements about this other than that the fused silica substrate of the mirrors is "transparent" at both visible and IR wavelengths.

The phase difference at the beam splitter of a LIGO-like interferometer is given by $$ \Delta \phi \simeq \frac{4\pi}{\lambda} h L\ , $$ where $h$ is the gravitational wave strain (assuming a polarisation aligned with the detector arms), $L$ is the effective arm length (increased by a large factor in the Fabry-Perot cavities) and $\lambda$ is the interferometer laser wavelength, and assuming the frequency is low enough to not be affected by the response roll-off of the Fabry-Perot cavities.

Why then does LIGO use an IR laser ($\lambda = 1064$ nm), rather than something with shorter wavelength that would produce a larger (and more detectable) phase difference?

I would think this probably has to do with how absorptive the optics are at different wavelengths, but cannot find definitive statements about this other than that the fused silica substrate of the mirrors is "transparent" at both visible and IR wavelengths.