Laser coherence control using homogeneous linewidth broadening
View Patent ↗An apparatus and method for linewidth broadening applied to a laser that emits a light having an output frequency ν and an emission linewidth δ E . The apparatus is equipped with an electro-optic modulator for intercepting the light and a noise generator for driving the electro-optic modulator with a radio-frequency (RF) noise signal spanning a frequency range selected to broaden the emission linewidth δ E of the light passing through the electro-optic modulator to a broadened linewidth δ B . The noise spectrum of the noise signal exhibits a continuous frequency range and can be flat or sloping. The range extends from low frequency ω L set below the emission linewidth δ E of the light to a high frequency ω H set above the emission linewidth δ E of the light. The electro-optic modulator can be selected from among many suitable devices including optical crystals. Further broadening can be achieved by employing one or more secondary EOMs operating in resonant or non-resonant modes. The lasers that benefit from the invention involve any type of inherently narrow bandwidth lasers operating in CW or pulsed modes.
1. An apparatus for linewidth broadening comprising:
a) a laser for emitting a light having an output frequency ν and an emission linewidth δ E ;
b) an electro-optic modulator for intercepting said light;
c) a noise generator for driving said electro-optic modulator with a radio-frequency noise signal spanning a predetermined frequency range such that said emission linewidth δ E is broadened to a broadened linewidth δ B ;
wherein said predetermined frequency range is a continuous frequency range commencing at a low frequency ω L below said emission linewidth δ E and terminating at a high frequency ω H above said emission linewidth δ E ;
wherein said noise generator comprises an amplification stage for amplifying said noise signal.
2. The apparatus of claim 1 , wherein said noise generator comprises a noise source and a filtering element.
3. The apparatus of claim 2 , wherein said filtering element
comprises a low-pass filter.
4. The apparatus of claim 2 , wherein said filtering element comprises a passband control for varying a passband of said filtering element.
5. The apparatus of claim 2 , wherein said radio-frequency noise generator has a substantially flat noise spectrum within said predetermined frequency range.
6. The apparatus of claim 2 , wherein said radio-frequency noise generator has a sloping noise spectrum within said predetermined frequency range.
7. The apparatus of claim 1 , wherein said electro-optic modulator comprises an optical crystal selected from the group consisting of lithium niobate, MgO-doped lithium niobate, potassium dihydrogen phosphate. (KDP), potassium dideuterium phosphate (KD*P), and potassium titanyl phosphate. (KTP).
8. An apparatus for linewidth broadening comprising:
a) a laser for emitting a light having an output frequency ν and an emission linewidth δ E ;
b) an electro-optic modulator for intercepting said light;
c) a noise generator for driving said electro-optic modulator with a radio-frequency noise signal spanning a predetermined frequency range such that said emission linewidth δ E is broadened to a broadened linewidth δ B ;
wherein said predetermined frequency range is a continuous frequency range commencing at a low frequency ν L below said emission linewidth δ E and terminating at a high frequency ω H above said emission linewidth δ E ;
further comprising an impedance matching circuit for matching the electrical impedance of said electro-optic modulator and said noise generator.
9. The apparatus of claim 8 , wherein said impedance matching circuit has an electrical impedance of about 50 Ohms.
10. The apparatus of claim 1 , further comprising at least one secondary electro-optic modulator for intercepting said light, said at least one secondary electro-optic modulator having a signal generator for applying to said at least one electro-optic modulator a secondary signal, such that said light is modulated by said secondary signal.
11. The apparatus of claim 10 , wherein said secondary signal generator comprises a single frequency generator such that said secondary signal comprises one frequency.
12. The apparatus of claim 10 , wherein said secondary electro-optic modulator is integrated with said electro-optic modulator.
13. The apparatus of claim 10 , wherein said secondary electro-optic modulator is positioned before said electro-optic modulator.
14. An apparatus for linewidth broadening comprising:
a) a laser for emitting a light having an output frequency ν and an emission linewidth δ E ;
b) an electro-optic modulator for intercepting said light;
c) a noise generator for driving said electro-optic modulator with a radio-frequency noise signal spanning a predetermined frequency range such that said emission linewidth δ E is broadened to a broadened linewidth δ B ;
wherein said predetermined frequency range is a continuous frequency range commencing at a low frequency ω L below said emission linewidth δ E and terminating at a high frequency ω H above said emission linewidth δ E ;
at least one secondary electro-optic modulator for intercepting said light, said at least one secondary electro-optic modulator having a signal generator for applying to said at least one electro-optic modulator a secondary signal, such that said light is modulated by said secondary signal;
wherein said secondary signal generator comprises a secondary noise generator such that said secondary signal is a secondary radio-frequency noise signal spanning a secondary frequency range.
15. The apparatus of claim 1 , wherein said laser is selected from the group consisting of edge-emitting diode lasers, surface-emitting lasers, gas lasers, solid-state lasers, external-cavity diode lasers, titanium-sapphire lasers, diode-pumped solid-state lasers, fiber lasers, and Neodymium-YAG lasers.
16. A method for linewidth broadening of a light emitted from a laser at an output frequency v and an emission linewidth 6 E, said method comprising:
a) intercepting said light with an electro-optic modulator;
b) driving said electro-optic modulator with a radio-frequency noise signal spanning a predetermined frequency range such that said light is modulated by said noise signal thereby broadening said emission linewidth δ E to a broadened linewidth δ B ;
wherein said predetermined frequency range is a continuous frequency range commencing at a low frequency ω L below said emission linewidth δ E and terminating at a high frequency ω H above said emission linewidth δ E ; and further comprising amplifying said noise signal.
17. The method of claim 16 , wherein said predetermined frequency range is selected such that said emission linewidth δ E is broadened substantially homogeneously.
18. The method of claim 16 , further comprising modulating said light with at least one secondary signal thereby further broadening said broadened linewidth δ B .
19. The method of claim 18 , wherein said at least one secondary signal comprises one frequency.
20. The method of claim 18 , wherein said at least one secondary signal spans a secondary frequency range.
21. An apparatus for linewidth broadening comprising:
a) a laser for emitting a light having an output frequency ν and an emission linewidth δ E ;
b) an electro-optic modulator for intercepting said light;
c) a noise generator for driving said electro-optic modulator with a radio-frequency noise signal spanning a predetermined frequency range such that said emission linewidth δ E is broadened to a broadened linewidth δ B ;
d) at least one secondary electro-optic modulator for intercepting said light, said at least one secondary electro-optic modulator having a secondary signal generator for applying to said at least one electro-optic modulator a secondary signal, such that said light is modulated by said secondary signal;
wherein said secondary signal generator comprises a secondary noise generator such that said secondary signal is a secondary radio-frequency noise signal spanning a secondary frequency range.