Characterization of near field transducers

• US 9,291,560 B2
• Filed: 03/11/2013
• Issued: 03/22/2016
• Est. Priority Date: 04/24/2012
• Status: Active Grant

• Current Assignee: Seagate Technology LLC (Seagate Technology Holdings Plc)
• Original Assignee: Seagate Technology LLC (Seagate Technology Holdings Plc)
• Inventors: Peng, Chubing, Zhou, Lifu
• Primary Examiner(s): Gaworecki, Mark R
• Application Number:
  US13/794,706
• Publication Number:
  US 20130277575A1
• Time in Patent Office: 1,107 Days
• Field of Search: 250/458.1, 250/459.1
• US Class Current: 1/1
• CPC Class Codes: G01N 21/64 Fluorescence; Phosphorescence
• CPC Class Codes: G01N 21/6489 Photoluminescence of semiconductors
• CPC Class Codes: G11B 2005/0021 Thermally assisted recording using an auxiliary energy source for heating the recording layer locally to assist the magnetization reversal
• CPC Class Codes: G11B 5/314 where the layers are extra layers normally not provided in the transducing structure, e.g. optical layers G11B5/3196 takes precedence
• CPC Class Codes: G11B 5/6088 Optical waveguide in or on flying head

Abstract

An approach for characterizing an optical near field transducer (NFT) involves providing excitation radiation to the NFT. The NFT emits photoluminescent radiation in response to the excitation radiation. The output radiation from the NFT is filtered so that a portion of the photoluminescent radiation emitted by the NFT passes through the filter and the excitation radiation is substantially blocked. A detector detects the portion of photoluminescent radiation and outputs an electrical signal in response to detection of the portion of photoluminescent radiation.

Claims

1. A system comprising:

a near field transducer (NFT) subassembly including an input coupler proximate a first surface and an NFT optical antenna proximate a second surface;

an excitation light source configured to provide excitation radiation to the near field transducer subassembly;

an optical filter configured to substantially pass a portion of photoluminescent radiation emitted by the NFT optical antenna in response to the excitation radiation and to substantially block the excitation radiation;

a detector configured to detect the portion of photoluminescent radiation and to output an output signal in response to detection of the portion of photoluminescent radiation;

a focusing lens configured to focus the excitation radiation onto the input coupler of the NFT subassembly; and

an objective lens configured to collect photoluminescent radiation emitted by the NFT toward the optical filter.

2. The system of claim 1, wherein the excitation radiation comprises femto-second or pico second laser pulses.

3. The system of claim 1, wherein the optical filter is configured to substantially pass radiation having wavelengths shorter than the excitation light.

4. The system of claim 1, further comprising an imaging subsystem configured to provide a visual image of the NFT.

5. The system of claim 4, wherein the imaging subsystem comprises:

a white light source; and

a charge coupled device (CCD).

6. The system of claim 1, wherein the detector comprises a photomultiplier tube (PMT).

7. The system of claim 1, further comprising an amplifier coupled to receive the output signal, wherein the amplifier is locked-in to a repetition frequency of the excitation radiation.

8. A system comprising:

an excitation light source configured to provide excitation radiation to a near field transducer (NFT) subassembly including an NFT optical antenna;

an optical filter configured to substantially pass a portion of photoluminescent radiation emitted by the NFT optical antenna in response to the excitation radiation and to substantially block the excitation radiation;

a detector configured to detect the portion of photoluminescent radiation and to output an output signal in response to detection of the portion of photoluminescent radiation; and

a monitoring subsystem configured to monitor the excitation radiation.

9. The system of claim 8, wherein the monitoring subsystem comprises:

an input side photodetector configured to generate a signal in response to the excitation radiation incident on the input side photodetector;

a beam splitter disposed in between the laser and the NFT subassembly, the beam splitter configured to split the excitation radiation so that a first portion of the excitation radiation travels along a first input path toward the input side photodetector and a second portion of the excitation radiation travels along a second input path toward the NFT subassembly.

10. The system of claim 8, wherein the monitoring subsystem comprises an output side photodetector configured to generate a signal in response to output radiation transmitted through the NFT subassembly, the output radiation dominated by the excitation radiation.

11. The system of claim 10, further comprising a beam splitter disposed between the NFT and the output side photodetector, the beam splitter configured to split the output radiation so that a first portion of the output radiation having wavelengths longer than an edge wavelength of the beam splitter travels along a first output path toward the output side photodetector and a second portion of the output radiation having wavelengths shorter than the edge wavelength travels along a second output path toward the detector.

12. A method, comprising:

providing excitation radiation to a near field transducer (NFT) subassembly;

filtering output radiation from the NFT subassembly, the filtering comprising passing a portion of photoluminescent radiation emitted by the NFT subassembly in response to the excitation radiation and substantially blocking the excitation radiation transmitted by the NFT subassembly; and

detecting the portion of photoluminescent radiation and generating an output signal in response to the detecting, wherein filtering the output radiation comprises filtering using one or more of a shortwave pass optical filter and a dichroic beam splitter.

13. The method of claim 12, wherein filtering the output radiation comprises filtering using a shortwave pass optical filter.

14. The method of claim 12, wherein filtering the output radiation comprises filtering using a dichroic beam splitter.

15. The method of claim 12, wherein detecting the portion of photoluminescent radiation comprises detecting using a photomultiplier tube.

16. The method of claim 12, wherein providing excitation radiation to an NFT subassembly comprises providing laser pulses at a repetition rate.

17. The method of claim 12, wherein filtering the output radiation from the NFT subassembly comprises substantially blocking the excitation radiation and substantially passing the portion of the photoluminescent radiation.

18. The method of claim 17, wherein blocking the excitation radiation comprises blocking the excitation radiation by a factor of about 10⁻

7.

19. A method, comprising:

providing excitation radiation to a near field transducer (NFT) subassembly;

filtering output radiation from the NFT subassembly, the filtering comprising passing a portion of photoluminescent radiation emitted by the NFT subassembly in response to the excitation radiation and substantially blocking the excitation radiation transmitted by the NFT subassembly;

detecting the portion of photoluminescent radiation and generating an output signal in response to the detecting; and

signal processing the output signal including amplifying the output signal using circuitry that locks into a repetition rate of the excitation radiation.