METHOD AND SYSTEM FOR GENERATION OF A NEEDLE-SHAPED BEAM BY A DIFFRACTIVE OPTICAL ELEMENT FOR USE IN EXTENDED DEPTH-OF-FOCUS OPTICAL COHERENCE TOMOGRAPHY

1 . A diffractive optical element comprising:

a substrate including a plurality of unit cells arrayed across the substrate, wherein each of the unit cells includes M phase elements and each of the M phase elements is characterized by one of a set of N phase values, wherein each of the set of N phase values is equal to an incremental phase value times an index m, wherein M>1 and m=1 . . . N.

2 . The diffractive optical element of claim 1 wherein the incremental phase value is equal to 2π/N.

3 . The diffractive optical element of claim 1 wherein 4<M<300.

4 . The diffractive optical element of claim 3 wherein M>N.

5 . The diffractive optical element of claim 1 wherein the substrate comprises fused silica.

6 . The diffractive optical element of claim 1 wherein the set of N phase values are distributed differently in at least two of the plurality of unit cells.

7 . The diffractive optical element of claim 1 wherein the set of N phase values are distributed randomly in the at least two of the plurality of unit cells.

8 . The diffractive optical element of claim 1 wherein the plurality of unit cells form a two-dimensional array.

9 . The diffractive optical element of claim 1 wherein each unit cell of the plurality of unit cells includes a predetermined number of phase elements characterized by the one of a set of N phase values.

10 . A method of generating a needle-shaped beam, the method comprising:

providing a diffractive optical element including a plurality of unit cells, wherein each unit cell of the plurality of unit cells includes a plurality of phase elements and each of the plurality of phase elements is characterized by a different phase value;

receiving an incident beam of light propagating in an axial direction;

directing the incident beam of light to pass through the diffractive optical element; and

generating a plurality of foci along the axial direction to form the needle-shaped beam.

11 . The method of claim 10 further comprising:

providing an objective lens; and

directing the incident beam of light to pass through the objective lens.

12 . The method of claim 11 wherein the incident beam of light passes through the objective lens after the incident beam of light passes though the diffractive optical element.

13 . The method of claim 10 wherein the needle-shaped beam is characterized by a depth of focus between 4 and 200 Rayleigh lengths.

14 . The method of claim 13 wherein the depth of focus is between 5 and 100 Rayleigh lengths.

15 . The method of claim 14 wherein the depth of focus is between 10 and 50 Rayleigh lengths.

16 . The method of claim 10 wherein the different phase values comprise a set of N phase values and each of the different phase values is equal to an incremental phase value times an index m, wherein m=1 . . . N.

17 . The method of claim 10 further comprising focusing the incident beam of light using a lens after the incident beam of light has passed through the diffractive optical element.

18 . The method of claim 17 further comprising scanning the incident beam of light after the incident beam of light has passed through the diffractive optical element.

19 . The method of claim 10 wherein the different phase values corresponding to each of the plurality of phase elements are distributed differently in at least two of the plurality of unit cells.

20 . The method of claim 10 wherein the plurality of unit cells form a two-dimensional array.