Abstract: The invention is directed to an improved cryogenic cooler with an expander where the regenerator matrix is decoupled from the displacer or piston, thereby allowing the design of each to be optimized substantially independently. The regenerator matrix is preferably positioned spaced apart from the displacer and can be designed to enhance thermal exchanges and flow rates of the working gas. In one embodiment, the regenerator matrix has a serpentine shape or U-shape disposed around the displacer and the cold finger. Preferably, the regenerator matrix is static. The thermal lengths of the cold finger and/or the displacer can be extended by minimizing their geometrical lengths. Additionally, the structural integrity or stiffness of the cold finger and/or displacer can be strengthened.