High-finesse optical resonator for cavity ring-down spectroscopy based upon Brewster's angle prism retroreflectors

• US 6,097,555 A
• Filed: 10/04/1999
• Issued: 08/01/2000
• Est. Priority Date: 10/21/1997
• Status: Expired due to Term

• Current Assignee: The Trustees of Princeton University (Princeton University)
• Original Assignee: The Trustees of Princeton University (Princeton University)
• Inventors: Rabinowitz, Paul, Lehmann, Kevin K.
• Primary Examiner(s): Shafer, Ricky D.
• Application Number:
  US09/412,069
• Time in Patent Office: 302 Days
• Field of Search: 359/831, 359/833, 359/834, 359/835, 359/836, 359/669, 356/300, 356/436, 356/437, 356/438, 356/439, 356/445, 372/16, 372/72, 372/92, 372/93, 372/95, 372/100
• US Class Current: 359/834
• CPC Class Codes: G01J 3/42 Absorption spectrometry; Double beam spectrometry; Flicker spectrometry; Reflection spectrometry beam switching arrangements G01J3/08
• CPC Class Codes: G02B 5/04 Prisms
• CPC Class Codes: G02B 5/12 Reflex reflectors

Abstract

A stable resonator for a ring-down cavity spectroscopy cell having an optic axis. The resonator includes two Brewster'"'"'s angle retroreflector prisms, each having a plurality of total internal reflection surfaces. The prisms are disposed in alignment along the optic axis of the resonator. One or both of the prisms can be rotated so that light rays enter and leave a surface of the prism nearly at Brewster'"'"'s angle to the normal of the prism surface. This feature maintains alignment between the prisms and allows the resonator to be tuned. One of the total internal reflection surfaces of at least one of the prisms may be a curved surface (either a ground curved surface or a surface curved by the addition, through optically contacting or gluing, of a plano-convex lens to the surface). Alternatively, an astigmatic lens may be centered in one arm of the resonator and tilted at Brewster'"'"'s angle with respect to the optic axis of the resonator. In a preferred embodiment, each of the prisms has an apex angle of about 135° minus Brewster'"'"'s angle, a second angle of about 90°, and a third angle of about 135° minus two times Brewster'"'"'s angle.

Claims

1. A resonator for a ring-down cavity spectroscopy cell having an optic axis, the resonator comprising:

a first Brewster'"'"'s angle retroreflector prism having a plurality of total internal reflection surfaces with one of the total internal reflection surfaces being a curved surface;

a second Brewster'"'"'s angle retroreflector prism having a plurality of total internal reflection surfaces and being disposed in alignment with the first prism along the optic axis of the resonator; and

means for rotating at least one of the prisms so that radiation enters and leaves a surface of each prism nearly at Brewster'"'"'s angle to the normal of the prism surface, whereby alignment between the prisms is maintained and the resonator is tuned.

2. The resonator as recited in claim 1 wherein the prisms are one of fused silica, sapphire, diamond, and calcium fluoride.

3. The resonator as recited in claim 1 wherein each of the prisms has an apex angle of about 135°

minus Brewster'"'"'s angle, a second angle of about 90°

, and a third angle of about 180°

minus two times Brewster'"'"'s angle.

4. The resonator as recited in claim 1 wherein the tangential curvature of the curved surface is 2n² √

2f and the sagittal curvature of the curved surface is √

2f, where f is the effective focal length of the curved surface and n is the index of refraction.

5. The resonator as recited in claim 1 further comprising means for coupling the radiation into and out of the resonator, the coupling means using frustrated total internal reflection.