Method and apparatus for stabilizing the thickness of an optical channel for extended pressure environments

A method for illuminating high pressure flowing fluid in a high pressure cell, comprising:

• providing the high pressure cell, including
• a first housing member and a second housing member,
• a spacer member held tightly between substantially planar surfaces of the first housing member and the second housing member, the spacer member having a thickness less than the first and second housing members,
• the spacer member having a hole therethrough with an edge of the hole defining a flow cavity between the first housing member and the second housing member,
• each of the first housing member and the second housing member having a groove for a gasket on a surface of the housing member that faces the spacer member, each groove surrounding and being larger than the hole through the spacer member,
• an inlet passage formed in either the first housing member or the second housing member extending from an outer face of the first or second housing member to the flow cavity,
• an outlet passage formed in either the first housing member or the second housing member and extending from an outer face of the first or second housing member to the flow cavity,
• an optical window in a mounting hole of the first housing member positioned with a surface of the optical window exposed to the flow cavity, wherein the at least one window has first portion at a first end with a substantially constant smaller cross sectional area, a second portion at a second end with a substantially constant larger cross sectional area, and a shoulder between the first and second portions, wherein the at least one window is positioned in the mounting hole with the first end facing the flow cavity,
• a compliant gasket positioned around the first portion of the window between the shoulder of the window and a corresponding first shoulder surface in the mounting hole, and
• an externally threaded retaining member having a central opening configured to let light pass through the retaining member along a main axis,
• the externally threaded retaining member being positioned in a threaded portion of the mounting hole, such that tightening the retaining member compresses the gasket against the first shoulder of the mounting hole, creating a static seal against fluid leaking past the window and positioning the window with an end face at the surface of the flow cavity;
• introducing high pressure fluid into the flow inlet such that the fluid flows through the flow cavity and exits through the flow outlet;
• and
• directing light through the optical window into the high pressure fluid in the flow cavity.