Coherent dynamically controllable narrow band light source

1. A coherent dynamically controllable narrow band light source, comprising:

a first sub-light source, said first sub-light source being electrically controllable such as to generate controllable time-dependent intensity patterns of light having a first wavelength;

a Raman active medium suitable to cause Raman scattering of light having said first wavelength;

a second sub-light source capable of emitting light with a second wavelength, said second wavelength being longer than said first wavelength; and

an optical fiber or waveguide, wherein said light emitted by said first and second sub-light sources traverses a length of said optical fiber or waveguide in a feed-forward configuration to facilitate a non-linear wavelength conversion step involving said Raman-active medium,

wherein at least one of said first and second sub-light sources has a coherence length longer than 0.5 mm, wherein the length of said fiber or waveguide is selected such as to allow for at least two consecutive Raman wavelength shifts, and wherein the frequency shift associated with the at least two Raman shifts is a corresponding multiple of the difference between said second and first wavelengths.

2. The light source of claim 1 , wherein the wavelength converted light resulting from said wavelength conversion step has a coherence length longer than 0.05 mm.

3. The light source of claim 1 , further comprising a modulator for modulating light generated by the first or second sub-light source, wherein said modulator is one of

an electro-optical modulator,

an acoustic-optical modulator, or

a swept Fabry-Perot filter,

wherein said modulator can be electronically controlled to generate one or more of:

a CW light signal,

a periodic sinusoidal modulation or

a light pulse pattern.

4. The light source of claim 3 , wherein the pulse lengths of the light pulse pattern are at least 10 ps and 50 ns or below.

5. The light source of claim 3 , wherein the modulator can be electronically controlled to configure the time delay between each two consecutive pulses with a mean repetition rate of 10 kHz or more.

6. The light source of claim 1 , wherein at least one of the first and second sub-light sources is a semi-conductor laser light source.

7. The light source of claim 1 , wherein at least one of the first and second sub-light sources has a spectral width narrower than 1 nm.

8. The light source of claim 1 , wherein said light source is operable with a duty cycle of less than 1%.

9. The light source of claim 1 , wherein the instantaneous power is more than 100 W.

10. The light source of claim 1 , said light source comprising at least one optical amplifier, wherein the at least one optical amplifier comprises a gain medium and a third sub-light source for pumping said gain medium.

11. The light source of claim 10 , wherein at least one of the optical amplifiers comprises a double clad fiber having a core portion formed by a rare-earth doped fiber and a cladding layer for guiding pump light, wherein said DUMP light is fed into the cladding layer in a direction opposite to the light propagating in the core portion.

12. The light source of claim 10 , wherein said light source comprises two or more optical amplifiers, wherein between two optical amplifiers, a filter, in particular a laser line filter, is provided for filtering an amplified stimulated emission background.

13. The light source of claim 1 , wherein said non-linear wavelength conversion step is carried out, at least in part, in an optical amplifier, wherein said second light signal is introduced into the optical amplifier prior to or during amplification in the amplifier where the wavelength conversion step takes place.

14. A method for generating coherent narrow band light comprising the following steps:

generating light having a first wavelength using a first sub-light source;

generating light having a second wavelength using a second sub-light source, said second wavelength being longer than said first wavelength; and

superposing said first and second wavelength light in an optical fiber or waveguide, thereby facilitating a non-linear wavelength conversion step involving a Raman-active medium,

wherein at least one of said first and second sub-light sources has a coherence length longer than 0.5 mm, wherein the length of said fiber or waveguide is selected such as to allow for at least two consecutive Raman wavelength shifts, and wherein the frequency shift associated with the at least two Raman shifts is a corresponding multiple of the difference between said second and first wavelengths.

15. The method of claim 14 , wherein the wavelength converted light resulting from said wavelength conversion step has a coherence length longer than 0.5 mm.

16. The method of claim 14 , further comprising a step of modulating light generated by the first or second sub-light source.

17. The method according to one of 14 , further comprising a step of amplifying light generated by one of said first and second sub-light sources, using an amplifier comprising a gain medium and a third sub-light source for pumping said gain medium, wherein said gain medium is a rare earth doped optical fiber.

18. The method of claim 14 , wherein the non-linear wavelength conversion step is carried out at least in part in an optical amplifier, wherein a light signal generated by said second sub-light source is introduced into the optical amplifier prior to or during amplification in the amplifier where at least part of the wavelength conversion step takes place.

19. The method of claim 14 , wherein a light signal generated by said second sub-light source is combined with light generated by the first sub-light source prior to a final amplification stage for amplifying said light generated by said first sub-light source.

20. The light source of claim 1 , wherein both of said first and second sub-light sources have a coherence length longer than 2 mm.