Terahertz measuring device and terahertz measuring method for measuring objects to be inspected

1. A terahertz measuring apparatus ( 1 , 101 ) for run-time wall thickness measurements of test objects ( 8 ), said terahertz measuring apparatus ( 1 , 101 ) comprising:

a transmitter and receiver unit ( 2 ; 2 a , 2 b ) for emitting a terahertz radiation ( 10 ) along an optical axis (A) and for receiving reflected terahertz radiation,

a controller and evaluation unit ( 3 ) for driving the transmitter and receiver unit ( 2 ; 2 a , 2 b ) and evaluating measuring signals (M) of the transmitter and receiver unit ( 2 ; 2 a , 2 b ),

wherein a beam splitting means ( 4 , 40 ) is provided to split up the emitted terahertz radiation ( 10 ) into at least

one first terahertz detection beam ( 10 a , 10 c ) along a first optical partial axis (A 1 ) and

one second terahertz detection beam ( 10 b , 10 d ) along a second optical partial axis (A 2 ) different from the first optical partial axis (A 1 ),

a reflection device ( 5 ) for reflecting the second terahertz detection beam ( 10 b , 10 d ) onto said test object ( 8 ) and reflecting the second terahertz detection beam ( 10 b ), reflected from said test object ( 8 ), back towards said beam splitting means ( 4 ) and/or said transmitter and receiver unit ( 2 ; 2 a , 2 b ),

said transmitter and receiver unit ( 2 ; 2 a , 2 b ) generating at least one measuring signal (M, M 1 , M 2 ) from the detection beams ( 10 a , 10 b , 10 c , 10 d ) reflected on said test object ( 8 ) and putting it out to said controller and evaluation unit ( 3 ) for determining at least one layer thickness of said test object ( 8 ).

2. The terahertz measuring apparatus ( 1 , 101 ) according to claim 1 , wherein said beam splitting means ( 4 , 40 ) reflects the terahertz detection beam ( 10 b , 10 d ) reflected from said test object ( 8 ) back towards said transmitter and receiver unit ( 2 ) along the optical axis (A) and/or passes the same.

3. The terahertz measuring apparatus ( 1 , 101 ) according to claim 1 , wherein said reflection device ( 5 ) reflects the second terahertz detection beam ( 10 b , 10 d ) at one or more mirror surfaces ( 5 a , 5 b ), e.g. each by 90°, and directs then onto said test object ( 8 ) in the second optical partial axis (A 2 ), and reflects the optical terahertz detection beam ( 10 b , 10 d ) reflected from said test object ( 8 ) back twice.

4. The terahertz measuring apparatus ( 1 , 101 ) according to claim 1 , wherein the optical path lengths of the first and second terahertz detection beams ( 10 a , 10 c , 10 b , 10 d ) are different from one another in such a way that the measurements in a common measuring signal (S) can be separated.

5. The terahertz measuring apparatus ( 1 , 101 ) according to claim 1 , wherein the first optical partial axis (A 1 ) and the second optical partial axis (A 2 ) are offset in relation to each other essentially by 90°, preferably in the same plane.

6. The terahertz measuring apparatus ( 1 , 101 ) according to claim 1 , wherein said beam splitting means is a beam splitter ( 4 ) partially passing the emitted terahertz radiation ( 10 ) as first partial terahertz radiation ( 10 a ) and partially reflecting it as second partial terahertz radiation ( 10 b ) to said reflection device ( 5 ), preferably at an angle of 90° compared to the optical axis (A),

said transmitter and receiver unit ( 2 ; 2 a , 2 b ) generating a common measuring signal (M) from the partial beams ( 10 a , 10 b ) reflected on said test object ( 8 ) and putting this out to said controller and evaluation unit ( 3 ).

7. The terahertz measuring apparatus ( 1 , 101 ) according to claim 1 , wherein said beam splitting means comprises an adjustable mirror ( 40 ) and an adjustment means ( 41 ) for adjusting said mirror ( 40 ),

said adjustable mirror ( 40 ) deflecting the emitted terahertz radiation ( 10 ) differently in a first position and second position, preferably without deflection in said first position and in said second with deflection at an angle of 90° compared to the optical axis (A),

said transmitter and receiver unit ( 2 ; 2 a , 2 b ) generating measuring signals (M 1 , M 2 ) from the detection beams ( 10 c , 10 d ) reflected at said test object ( 8 ) and putting the same out to said to said controller and evaluation unit ( 3 ).

8. The terahertz measuring apparatus ( 1 ) according to claim 1 , wherein a combined transmitter and receiver unit ( 2 ), e.g. a THz transceiver, is provided both for emitting as well as for receiving the terahertz radiation ( 10 ).

9. The terahertz measuring apparatus ( 101 ) according to claim 1 , wherein

a receiver unit ( 2 b ) is provided separate from a transmitter unit ( 2 a ),

whereby the terahertz radiation ( 10 ) emitted by the transmitter unit ( 2 a ) is split up by said beam splitting means ( 4 , 40 ) into the two terahertz detection beams ( 10 a , 10 b , 10 c , 10 d ), and the terahertz detection beam ( 10 a , 10 c ) reflected from said test object ( 8 ) and the terahertz detection beam ( 10 b , 10 d ) reflected from said test object ( 8 ) and said reflection device ( 5 ) each pass said beam splitting means ( 4 , 40 ).

10. The terahertz measuring apparatus ( 1 , 101 ) according to claim 9 , wherein said receiver unit ( 2 b ) receives the terahertz-radiation ( 10 b , 10 d ) passed by said beam splitting means ( 4 , 40 ) and the terahertz detection beam ( 10 a , 10 c ) reflected by said beam splitting means ( 4 , 40 ).

11. The terahertz measuring apparatus ( 1 , 101 ) according to claim 1 , wherein in the optical axis (A) and/or in the optical partial axes (A 1 , A 2 ) beam guiding elements are provided for focusing the beam.

12. The terahertz measuring apparatus according to claim 1 , wherein terahertz radiation ( 10 ) in a frequency range of between 10 GHz and 10 THz is utilized.

13. An arrangement comprising the measuring device ( 1 , 101 ) according to claim 1 and the test object ( 8 ),

whereby the optical path of the second terahertz detection beam ( 10 b , 10 d ) from the beam splitting means ( 4 , 40 ) via the reflection device ( 5 ) to the first point of impingement onto the test object ( 8 ) and back via the reflection device ( 5 ) to the beam splitting means ( 4 , 40 ) ( 4 , 40 ) is longer than the entire optical path of the first terahertz detection beam ( 10 a ) from the beam splitter ( 4 ) through the test object ( 8 ) and back to the beam splitter ( 4 ), for separating the first measuring peaks (P 1 , P 2 , P 3 , P 4 ) of the first terahertz detection beam ( 10 a , 10 c ) and the second measuring peaks (P 5 , P 6 , P 7 , P 8 ) of the second terahertz detection beam ( 10 b , 10 d ).

14. The arrangement according to claim 13 , wherein a common measuring signal (S) for both measurements is provided and the second measuring peaks (P 5 , P 6 , P 7 , P 8 ) of the second partial terahertz beam ( 10 b ) in the common measuring signal (M) are received by the transmitter and receiver unit ( 2 ; 2 a , 2 b ) separately from the first measuring peaks (P 1 , P 2 , P 3 , P 4 ), preferably after the former or alternatingly.

15. A terahertz measuring method for measuring a test object ( 8 ), comprising at least the following steps:

emitting a terahertz beam ( 10 ) along an optical axis (A) towards a beam splitting means ( 4 , 40 ),

splitting up the terahertz radiation ( 10 ) into at least one first terahertz detection beam ( 10 a , 10 c ) and one second terahertz detection beam ( 10 b , 10 d ),

putting out the first terahertz detection beam ( 10 a, c ) along a first optical partial axis (A 1 ) onto the test object ( 8 ) and reflecting back the first terahertz detection beam ( 10 a, c ) on boundary surfaces of the test object ( 8 ) as reflected first terahertz detection beam ( 10 a ) towards the beam splitting means ( 4 , 40 ),

putting out the second terahertz detection beam ( 10 b, d ) via a reflection device ( 5 ) including reflecting at least once on the reflection device ( 5 ), and aligning the second terahertz detection beam ( 10 b, d ) along a second optical partial axis (A 2 ) different from the first optical partial axis (A 1 ) onto the test object ( 8 ),

reflecting back the second partial terahertz beam ( 10 b ) reflected from the test object ( 8 ) towards the beam splitting means ( 4 , 40 ),

guiding the reflected first and second terahertz detection beam ( 10 a , 10 b , 10 c , 10 d ) from the beam splitting means ( 4 , 40 ) towards the transmitter and receiver unit ( 2 ; 2 a , 2 b ) and receiving the same in the transmitter and receiver unit ( 2 ; 2 a , 2 b ),

generating at least one measuring signal (M, M 1 , M 2 ) and evaluating said measuring signal (M M 1 , M 2 ) and determining layer thicknesses of the test object ( 8 ).

16. The measuring method according to claim 15 , wherein the emitted terahertz radiation ( 10 ) is split up, by means of a beam splitter ( 4 ) serving as beam splitting means, simultaneously into a first partial beam ( 10 a ) representing the first detection beam and a second partial beam ( 10 b ) representing the second detection beam, and following reflection on the test object ( 8 ), is re-merged and subsequently incorporated in a common measuring signal (M).

17. The measuring method according to claim 16 , wherein the second terahertz radiation ( 10 b ) is emitted in an optical path which is longer compared to the first partial terahertz beam ( 10 a ) in such a way that the duration of the first measuring signal (M 1 ) of the first partial terahertz beam ( 10 a ) is shorter than the temporal delay (Δt) of the second measuring signal (M 2 ) in relation to the first measuring signal (M 1 ), and the two measuring signals (M 1 , M 2 ) of the partial terahertz beams ( 10 a , 10 b ) are present in the common measuring signal (M) separated in time.

18. The measuring method according to claim 15 , wherein, as beam splitting means, an adjustable mirror ( 40 ) is adjusted between a first and second position, in which it deflects the THZ radiation along different optical partial axes (A 1 , A 2 ).