Coherent periodically pulsed radiation spectrometer

• US 5,748,309 A
• Filed: 10/19/1995
• Issued: 05/05/1998
• Est. Priority Date: 10/20/1994
• Status: Expired due to Term

• Current Assignee: Daniel W. Van Der Weide, Keilmann Fritz
• Original Assignee: Max-Planck-Gesellschaft Zur Foerderung Der Wissenschaften e.V. (Max-Planck-Gesellschaft zur Frderung der Wissenschaften e)
• Inventors: Keilmann, Fritz, van der Weide, D. W.
• Primary Examiner(s): HANTIS, KAREN
• Application Number:
  US08/545,136
• Time in Patent Office: 929 Days
• Field of Search: 356/318, 356/326, 356/349, 356/344, 356/346, 356/328, 250/458.1, 250/459.1, 250/461.1, 250/461.2, 250/338.5
• US Class Current: 356/326
• CPC Class Codes: G01J 3/4338 Frequency modulated spectrometry

Abstract

A spectroscopy method is defined in which a first source of radiation (51) emits a periodically pulsed beam (A) having a repetition frequency ω and in that a second source of radiation (52) emits a periodically pulsed beam (B) having a repetition frequency ω+Δ, the beams are united with each other and directed at a material specimen (6) to be analyzed and a detector means determines the amplitudes of the frequency components nΔ of the beam emanating from the material specimen.

Claims

1. A spectroscopy method for determining spectroscopic properties of a specimen (6) said method using coherent periodically pulsed radiation, comprising the steps of:

emission of a periodically pulsed beam (A) with a repetition frequency ω

by a first source of radiation (51);

emission of a periodically pulsed beam (B) having a repetition frequency ω

+Δ

by a second source of radiation (52), wherein a component Δ

is smaller than ω

, said periodically pulsed radiation being formed from said beams (A,B);

wherein each pulse of said pulsed beams (A) and (B) being formed by components ω

, 2ω

, 3ω

, . . . and (ω

+Δ

), 2(ω

+Δ

), 3(ω

+Δ

), . . . , which are higher multiples of the repetition frequencies, respectively;

combination of said pulsed beams (A) and (B) into a common time-coherent beam and simultaneous irradiation of said specimen (6) by said common time-coherent beam; and

simultaneous detection of radiation being transmitted or reflected by said specimen (6) due to said irradiation to a detector means (7) in which amplitudes of frequency components Δ

, 2Δ

, . . . , nΔ

are determined, which amplitudes allow the determination of said spectroscopic properties at frequencies corresponding to ω

+Δ

, 2(ω

+Δ

), . . . , n(ω

+Δ

).

2. The spectroscopy method as set forth in claim 1, wherein said beams (A, B) are emitted by said first and second sources of radiation (51, 52) perpendicularly polarized on each other.

3. The spectroscopy method as set forth in claim 1, wherein said first and second sources of radiation (51, 52) are arranged spatially separated from each other.

4. The method as set forth in claim 1, wherein said periodically pulsed radiation is formed from said beams (A, B) by the further steps of combination of said beams (A, B) with each other and application thereof together with a further beam, the frequency Ω

of which being greater than the highest frequency component contained in said beams (A, B), to an upconversion means an output radiation of which forming said periodically pulsed radiation.

5. The method as set forth in claim 4, wherein said output radiation contains frequency components Ω

+nω and

Ω

+n(ω

+Δ

) and wherein the frequency components Ω

-nω

, Ω

-n(ω

+Δ

) and nω

are suppressed by said upconversion means, wherein n=1, 2 . . . .

6. The method as set forth in claim 1, wherein a visible laser beam is added to a trace of said periodically pulsed radiation and said radiation being transmitted or reflected.

7. The method as set forth in claim 6, characterized in that said visible laser beam is modulated with said component Δ

and is used as a reference in frequency analysis of an output signal of said detector device.

8. The method as set forth in claim 7, characterized in that the time-dependent variations of Δ

are recorded and frequency analysis data are corrected accordingly.

9. A spectrometer for determining spectroscopic properties of a specimen (6) said spectrometer providing time-coherent periodically pulsed radiation, comprising:

a first source of radiation (51) for emitting a periodically pulsed beam (A) with a repetition frequency ω

;

a second source of radiation (52) for emitting a periodically pulsed beam (B) with a repetition frequency ω

+Δ

, wherein a component Δ

is smaller than Δ

;

wherein each pulse of said pulsed beams (A) and (B) comprising components ω

, 2ω

, 3ω

, . . . and (ω

+Δ

), 2(ω

+Δ

), 3(ω

+Δ

), . . . , which are higher multiples of the repetition frequencies, respectively;

means (53) for combining said pulsed beams (A) and (B) into a common time-coherent beam of said periodically pulsed radiation;

so as to provide simultaneous irradiation of said periodically pulsed radiation to said specimen (6); and

detector means (7) for detecting radiation being transmitted or reflected by said specimen (6) due to said irradiation in which said detector means (7) amplitudes of frequency components Δ

, 2Δ

, . . . , nΔ

are determined, which amplitudes allow the determination of said spectroscopic properties at frequencies corresponding to ω

+Δ

, 2(ω

+Δ

), . . . , n(ω

+Δ

).

10. The spectrometer as set forth in claim 9, wherein said first and second sources of radiation (51, 52) each include a signal generator (511, 521) and a non-linear circuit (NLC) (512, 522) coupled thereto.

11. The spectrometer as set forth in claim 9, wherein said detector means (7) includes a bolometer.

12. The spectrometer as set forth in claim 9, wherein said means for combining comprises a combiner (53) which is disposed in a radiation path between said first and second sources of radiation (51, 52) and said specimen (6).

13. The spectrometer as set forth in claim 12, wherein said means for combining comprises a dual antenna.

14. The spectrometer as set forth in claim 12, wherein said means for combining further comprises an upconversion means being adapted to receive said beams (A, B) and a beam with a frequency Ω

from a further source of radiation.

15. The spectrometer as set forth in claim 9, wherein a combiner is disposed in a trace between said specimen (6) and said detector means (7).