A liquid sample analyzer comprising: a liquid sample source; a flow cell configured to receive a flow of a liquid sample from the liquid sample source, the flow cell including a window; an optical device (20, 24); and a plurality of optical fibers optically connecting the flow cell to the optical device (20,24) to transmit light between the flow cell and the optical device (20, 24); wherein: the plurality of optical fibers are configured as a fiber optic bundle having a first terminal end coupled to the flow cell; each of the optical fibers includes a first optical fiber end face on the first terminal end of the fiber optic 2. bundle; the first optical fiber end faces collectively form a first fiber bundle end face at the first terminal end of the fiber optic bundle; and the first fiber bundle end face is retained in intimate contact with the window; the optical device is a light source or a monochromator optically interposed between a light and the flow cell; the window is an excitation light entrance window to receive excitation light from the optical device (20, 24); the liquid sample analyzer includes a fluorescence detector; the flow cell includes an emission light exit window to transmit fluorescent emission light from the liquid sample in the flow channel (154, 254) from the flow cell to the fluorescence detector; the emission light exit window is oriented at an angle of about 90 degrees with respect to the excitation light entrance window; the fiber optic bundle further includes a second terminal end coupled to the optical device (20, 24) each of the optical fibers further includes a second optical fiber end face opposing its first optical fiber end face; the second optical fiber end faces collectively form a second fiber bundle end face at the second terminal end of the fiber optic bundle; and the first and second fiber bundle end faces (112A, 112B) have different dimensional configurations from one another. a liquid sample source; a flow cell configured to receive a flow of a liquid sample from the liquid sample source, the flow cell including a window; an optical device (20, 24); and a plurality of optical fibers optically connecting the flow cell to the optical device (20,24) to transmit light between the flow cell and the optical device (20, 24); wherein: the plurality of optical fibers are configured as a fiber optic bundle having a first terminal end coupled to the flow cell; each of the optical fibers includes a first optical fiber end face on the first terminal end of the fiber optic 2. bundle; the first optical fiber end faces collectively form a first fiber bundle end face at the first terminal end of the fiber optic bundle; and the first fiber bundle end face is retained in intimate contact with the window; the optical device is a light source or a monochromator optically interposed between a light and the flow cell; the window is an excitation light entrance window to receive excitation light from the optical device (20, 24); the liquid sample analyzer includes a fluorescence detector; the flow cell includes an emission light exit window to transmit fluorescent emission light from the liquid sample in the flow channel (154, 254) from the flow cell to the fluorescence detector; the emission light exit window is oriented at an angle of about 90 degrees with respect to the excitation light entrance window; the fiber optic bundle further includes a second terminal end coupled to the optical device (20, 24) each of the optical fibers further includes a second optical fiber end face opposing its first optical fiber end face; the second optical fiber end faces collectively form a second fiber bundle end face at the second terminal end of the fiber optic bundle; and the first and second fiber bundle end faces (112A, 112B) have different dimensional configurations from one another.