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 ; and a plurality of optical fibers optically connecting the flow cell to the optical device to transmit light between the flow cell and the optical device ; 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 ; 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 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 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 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 ; and a plurality of optical fibers optically connecting the flow cell to the optical device to transmit light between the flow cell and the optical device ; 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 ; 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 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 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 have different dimensional configurations from one another. <EOS>