Microscope and interferometer thereof

An interferometer comprises a light source unit, a first splitter, a reference beam unit and a detection unit. The light source unit provides a laser beam. The first splitter receives the laser beam from the light source unit and splits the laser beam into a first beam and a second beam. The reference beam unit comprises a frequency shifter, a stopper and a spherical mirror. A center of the frequency shifter is located on a curvature center of the spherical mirror, the first beam traveling from the first splitter to the frequency shifter, the frequency shifter splitting the first beam into a diffraction beam and a zero-order beam, wherein the diffraction beam travels to the spherical mirror, reflected by the spherical mirror toward the frequency shifter, passing the frequency shifter to become a reference beam, and the zero-order beam is stopped by the stopper. The detection unit receives the reference beam from the reference beam unit.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to a microscope, and in particular to a microscope utilizing multi-wavelength laser beams.

2. Description of the Related Art

FIG. 1ashows a conventional microscope1comprising a light source unit10, a splitter21, a splitter22, a reflector31, a reflector32, a reflector33, a frequency shifter40, a stopper50, a photoelectric detector60and probe70. A laser beam11is emitted from light source unit10, passing splitter21and split into a first beam12and a second beam13. First beam12is reflected by reflector31toward frequency shifter40, and split into a diffraction beam14and a zero-order beam15. Zero-order beam15is stopped by stopper50. Diffraction beam14passes reflector32, splitter22and reflector33to photoelectric detector60. Second beam13passes splitter22to probe70to detect sample80.

When a wavelength of incident laser changes, the direction of diffraction beam of laser changes correspondingly to fail the interferometer. With reference toFIG. 1b, when laser beam11′ with improper wavelength is projected to frequency shifter40, a corresponding diffraction beam16is generated. However, the light path of diffraction beam16is different from diffraction beam14. The difference in wavelength of laser beam changes the corresponding light path thereof. Diffraction beam16cannot be projected onto photoelectric detector60. Thus, conventional interferometer microscope1only can detect a sample with a single-wavelength laser beam, not a multi-wavelength laser beam.

BRIEF SUMMARY OF THE INVENTION

The invention relates to an interferometer comprising a light source unit, a first splitter, a reference beam unit and a detection unit. The light source unit provides a laser beam. The first splitter receives the laser beam from the light source unit and splits the laser beam into a first beam and a second beam. The reference beam unit comprises a frequency shifter, a stopper and a spherical mirror. A center of the frequency shifter is located on a curvature center of the spherical mirror, the first beam traveling from the first splitter to the frequency shifter, the frequency shifter splitting the first beam into a diffraction beam and a zero-order beam, wherein the diffraction beam travels to the spherical mirror, reflected by the spherical mirror toward the frequency shifter, passing the frequency shifter to become a reference beam, and the zero-order beam is stopped by the stopper. The detection unit receives the reference beam from the reference beam unit.

The microscope utilizing the interferometer of the invention can detect samples with different wavelength of laser beams.

DETAILED DESCRIPTION OF THE INVENTION

The invention relates to an interferometer comprising a light source unit, a first splitter, a reference beam unit and a detection unit. The light source unit provides a laser beam. The first splitter receives the laser beam from the light source unit and splits the laser beam into a first beam and a second beam. The reference beam unit comprises a frequency shifter, a stopper and a spherical mirror. A center of the frequency shifter is located on a curvature center of the spherical mirror, the first beam traveling from the first splitter to the frequency shifter, the frequency shifter splitting the first beam into a diffraction beam and a zero-order beam, wherein the diffraction beam travels to the spherical mirror, reflected by the spherical mirror toward the frequency shifter, passing the frequency shifter to become a reference beam, and the zero-order beam is stopped by the stopper. The detection unit receives the reference beam from the reference beam unit.

The interferometer of the invention can be utilized in scattering-type scanning near-field optical microscopy (s-SNOM), apertureless scanning near-field optical microscopy, photon tunneling microscopy, near-field plasmon microscopy, etc.

FIG. 2ashows a microscope100of a first embodiment utilizing the interferometer of the invention, comprising a light source unit110, a major optical unit120, a reference beam unit130and a detection unit140. The major optical unit120comprises an expanding lens module121, a first splitter123, a focusing lens124and a probe125. The reference beam unit130comprises an expanding lens module131(providing expanding and focusing functions according to the direction of beam), a rectangular prism132, a reflector133, a lens134, an acoustoptic frequency shifter135, a stopper136and a spherical mirror137. The light source unit110provides a laser beam101. The laser beam101passes the expanding lens module121to the first splitter123. The first splitter123splits the laser beam101into a first beam102and a second beam103. The first beam102passes the expanding lens module131, the rectangular prism132, the reflector133, the lens134, and is focused on the acoustooptic frequency shifter135. The acoustooptic frequency shifter135splits the first beam102into a diffraction beam104and a zero-order beam105. The diffraction beam104is projected to the spherical mirror137. The zero-order beam105is stopped by stopper136. The second beam103passes the focusing lens124projected on the probe125to detect the sample126.

The laser beam101comprises a first frequency W, the frequency shifter135provides a frequency shift F, the diffraction beam104comprises a second frequency W+F, and a diffraction angle thereof is a function of a wavelength11of the laser beam104. The frequency of the zero-order beam105is equal to the first frequency W.

The lens134comprises a focal length R1, the spherical mirror137comprises a radius R2, and the focal length R1equals the radius R2. A center of the acoustooptic frequency shifter135is located on a curvature center of the spherical mirror137. With reference toFIG. 2b, when the diffraction beam104is reflected by the spherical mirror137, the diffraction beam104travels along the original path back to the center of the acoustooptic frequency shifter135to become a reference beam106. The reference beam106comprises a third frequency W+2F. The reference beam106travels from the acoustooptic frequency shifter135, passing the lens134, the reflector133, the rectangular prism132, the expanding lens module131and the first splitter123to the detection unit140.

The microscope100of the invention utilizes multi-wavelength laser beams. With reference toFIG. 3a, a laser beam101′ with a wavelength λ2is utilized in detection, it is split by the first splitter123into a first beam102′ and a second beam103′. The acoustooptic frequency shifter135splits the first beam102′ into a diffraction beam104′ and a zero-order beam105′. The wavelength of the laser beam101′ is different from the wavelength of the laser beam101. Thus, the projection location of the diffraction beam104′ on the spherical mirror137is different from that of the diffraction beam104. However, because the center of the acoustooptic frequency shifter135is located on the curvature center of the spherical mirror137, with reference toFIG. 3b, the diffraction beam104′ is reflected by the spherical mirror toward the center of the acoustooptic frequency shifter135to become a reference beam106′.

The microscope of the invention therefore can detect samples with different wavelength of laser beams.

FIG. 4shows a detailed structure of the light source unit110, comprising a first light source111, a second light source112and a third light source113. The first light source111provides a frequency stabilized laser111′. The second light source112provides a multi-wavelength laser112′. The third light source113provides a pulsed laser113′. The frequency stabilized laser111′ can be a frequency stabilized He—Ne laser. The multi-wavelength laser112′ can be a multi-wavelength Argon laser. The pulsed laser113′ can be a Ti-sapphire laser. The frequency stabilized laser111′ is base beam and calibrated beam. The multi-wavelength laser112′ provides multi-wavelength property. The pulsed laser113′ provides continuous white light source.

The detection unit140comprises a photoelectric detector to receive data in the light beams projected thereto.

FIG. 5ashows a microscope100′ of a modified embodiment of the invention, wherein the spherical mirror is replaced by a convex lens138and a reflector139. The center of the acoustooptic frequency shifter135is located on a focal point of the convex lens138. With reference toFIG. 5b, when the diffraction beam104is reflected by the reflector139, the diffraction beam104travels along the original path, passing the convex lens138back to the center of the acoustooptic frequency shifter135to become a reference beam106.

FIG. 6ashows a microscope200of a second embodiment of the invention, comprising a light source unit210, a major optical unit220, a reference beam unit230and detection unit240. The major optical unit220comprises an expanding lens module221, a second splitter223, a focusing lens224and a probe225. The reference beam unit230comprises a half-wave plate2301, a first splitter2302, a quarter-wave plate2311, a lens2312, an acoustooptic frequency shifter2313, a stopper2314, a spherical mirror2315, a rectangular prism2321, a reflector2322, an expanding lens module2323and a reflector2324. The laser beam201passes the half-wave plate2301to the first splitter2302. The first splitter2302splits the laser beam201into a first beam202and a second beam203. The first beam202passes the quarter-wave plate2311, the lens2312and focuses on the acoustooptic frequency shifter2313. The acoustooptic frequency shifter2313splits the first beam202into a diffraction beam204and a zero-order beam205. The diffraction beam204is projected to the spherical mirror2315. The zero-order beam205is stopped by the stopper2314. The second beam203passes the expanding lens module221, the second splitter223and focusing lens224to the probe225to detect sample126.

In the second embodiment, the first splitter2302is a linear polarization splitter.

The laser beam201comprises a first frequency W, the frequency shifter2313provides a frequency shift F, the diffraction beam204comprises a second frequency W+F, and a diffraction angle thereof is a function of a wavelength λ1of the laser beam. The frequency of the zero-order beam205is equal to the first frequency W.

The lens2312comprises a focal length R1, the spherical mirror2315comprises a radius R2, and the focal length R1equals the radius R2. A center of the acoustooptic frequency shifter2313is located on a curvature center of the spherical mirror2315. With reference toFIG. 6b, when the diffraction beam204is reflected by the spherical mirror2315, the diffraction beam204travels along the original path back to the center of the acoustooptic frequency shifter2313to become a reference beam206. The reference beam206comprises a third frequency W+2F. The reference beam206travels from the acoustooptic frequency shifter2313, passing the lens2312, the quarter-wave plate2311, the first splitter2302, the rectangular prism2321, the reflector2322, the expanding lens module2323, the reflector2324and the second splitter223to the detection unit240.

The microscope200comprises a different light path from that of the microscope100. Additionally, the microscope200has lower noise.

The lenses in the embodiments are achromatic lenses.