Laser Repetition Rate Multiplier And Flat-Top Beam Profile Generators Using Mirrors And/or Prisms

Patent metadata

Field	Value
Publication number	US-2016359292-A1
Application number	US-201615239268-A
Country	US
Kind code	A1
Filing date	Aug 17, 2016
Priority date	Jun 20, 2014
Publication date	Dec 8, 2016
Grant date	—

Abstract

A repetition rate (pulse) multiplier includes one or more beam splitters and prisms forming one or more ring cavities with different optical path lengths that delay parts of the energy of each pulse. A series of input laser pulses circulate in the ring cavities and part of the energy of each pulse leaves the system after traversing the shorter cavity path, while another part of the energy leaves the system after traversing the longer cavity path, and/or a combination of both cavity paths. By proper choice of the ring cavity optical path length, the repetition rate of an output series of laser pulses can be made to be a multiple of the input repetition rate. The relative energies of the output pulses can be controlled by choosing the transmission and reflection coefficients of the beam splitters. Some embodiments generate a time-averaged output beam profile that is substantially flat in one dimension.

First claim

1 . A laser pulse repetition rate multiplier for receiving input laser pulses and for generating output pulses with an output pulse repetition rate that is more than two times that of the input laser pulses, the laser pulse repetition rate multiplier comprising:
a Herriott cell including first and second curved mirrors, first and second beam splitters and at least two fold mirrors forming an optical cavity, and a right-angled prism positioned outside of the optical cavity, the Herriot cell being configured such that portions of each said input pulse are transmitted along a primary cavity loop inside the optical cavity, then passed to the right-angled prism, then transmitted along a secondary cavity loop inside the optical cavity before exiting the optical cavity as one of said generated output pulses, wherein the two curved mirrors have a radius of curvature approximately equal to an odd integer multiple of one fourth of a spatial separation between said input laser pulses, and wherein the two curved mirrors have a common radius of curvature and are separated by a distance substantially equal to the radius of curvature.

2 . The laser pulse repetition rate multiplier of claim 1 , wherein the Herriot cell is configured such that the output pulse repetition rate is four times that of the original input pulses.

3 . The laser pulse repetition rate multiplier of claim 1 ,
wherein the Herriot cell is configured such that at least a portion of each said input laser pulse is directed by the first beam splitter such that it is reflected by first portions of the first and second curved mirrors while on the primary cavity loop, and is directed by the second beam splitter such that it is reflected by second portions of the first and second curved mirrors while on the secondary cavity loop, wherein said Herriot cell further comprises a prism disposed in the primary cavity loop, and wherein one of the prism, the at least two fold mirrors, and the right-angle prism is configured to divert laser pulses coming out from the primary cavity loop into the secondary cavity loop.

4 . The laser pulse repetition rate multiplier of claim 3 , wherein the Herriot cell is configured such that the primary cavity loop lies in a different plane than the secondary cavity loop.

5 . The laser pulse repetition rate multiplier of claim 4 , wherein the first beam splitter receives said input laser pulses and reflects approximately two-thirds of the energy of each said input laser pulse into the primary cavity loop.

6 . The laser pulse repetition rate multiplier of claim 1 wherein second beam splitter has a reflectivity of approximately one-third.

7 . The laser pulse repetition rate multiplier of claim 1 , wherein the Herriot cell is configured such that:
each said input laser pulse is directed onto the first beam splitter; the first beam splitter is configured to direct at least a first portion of said each input laser pulse such that the first portion is reflected by the first and second curved mirrors in a first plane while on the primary cavity loop, and then directed toward said right-angle prism; the right-angle prism is configured to redirect the first portion to the second beam splitter; and the second beam splitter is configured to direct at least a second portion of each said first portion such that the second portion is reflected by the first and second curved mirrors in a second plane while on the secondary cavity loop, the second plane being different from the first plane.

8 . The laser pulse repetition rate multiplier of claim 1 ,
wherein the Herriot cell further comprises one of a beam compensator and prism disposed with the first beam splitter in a first plane, and wherein the second beam splitter and the at least two fold mirrors are disposed in a second plane.

9 . A repetition rate multiplier for receiving input laser pulses and for generating output pulses with an output pulse repetition rate that is at least two times that of the input laser pulses, the laser pulse repetition rate multiplier comprising:
at least one beam splitter and two light reflective elements forming a ring cavity, wherein the beam splitter is configured to direct a first energy fraction of each input laser pulse such that the first fraction exits the repetition rate multiplier at a first time, and configured to direct a second fraction of the energy of the input laser pulse into the ring cavity such that the second fraction is reflected between the two reflective elements and exits the repetition rate multiplier at a second time.

10 . The repetition rate multiplier of claim 9 , wherein said two light reflective elements include two right-angle light reflective elements comprising one of two right-angle mirror elements and two right-angle prisms.

11 . The repetition rate multiplier of claim 10 , wherein the beam splitter is further positioned to direct the second energy fraction of each said input laser pulse out of the repetition rate multiplier after the second energy fraction traverses between the first and second right-angle reflective elements at least once.

12 . The repetition rate multiplier of claim 11 , wherein the first fraction is approximately one-third of a total energy of said each input laser pulse.

13 . The repetition rate multiplier of claim 11 , wherein the second fraction is approximately two-thirds of a total energy of said each input laser pulse.

14 . The repetition rate multiplier of claim 11 , wherein one of said right-angle reflective elements is rotated relative to the other said right-angle reflective-pair element such that the second fraction of each said input laser pulse travels multiple times around the ring cavity before returning to close to its original location on the beam splitter.

15 . The repetition rate multiplier of claim 10 , wherein said ring cavity further comprises at least one lens configured such that each laser pulse directed through said ring cavity is substantially refocused each time that the laser pulse traverses the ring cavity.

16 . The repetition rate multiplier of claim 15 , wherein at least one spherical lens in the ring cavity refocuses each laser pulse.

17 . The repetition rate multiplier of claim 15 , wherein at least one pair of cylindrical lenses in the ring cavity refocuses each laser pulse.

18 . The repetition rate multiplier of claim 17 , wherein the cylindrical lenses are substantially at Brewster's angle relative to the laser beam path and polarization.

19 . The repetition rate multiplier of claim 9 , wherein said two light reflective elements comprise a first curved mirror and a second curved mirror.

20 . The repetition rate multiplier of claim 19 , wherein said at least one beam splitter includes:
a first beam splitter configured to direct said first and second energy fractions into the ring cavity, and a second beam splitter configured to direct the second energy fraction of each said input laser pulse out of the repetition rate multiplier after the second energy fraction traverses between the first and second reflective elements at least once.

21 . The repetition rate multiplier of claim 20 , further comprising:
a prism disposed in the ring cavity, at least two fold mirrors disposed in the ring cavity; and a right-angled prism positioned outside of the ring cavity, wherein the first beam splitter and the prism are configured such that first portions of each said input pulse are transmitted along a primary cavity loop inside the ring c

Assignees

• Kla Tencor Corp

Inventors

• Chuang Yung-Ho Alex
• Lu Xiaoxu
• Liou Justin Dianhuan
• Armstrong J Joseph
• Deng Yujun
• Fielden John

Classifications

• H01S3/005

  Optical devices external to the laser cavity, specially adapted for lasers, e.g. for homogenisation of the beam or for manipulating laser pulses, e.g. pulse shaping (shaping laser beam for working metal or other materials B23K26/06; optical elements, systems or apparatus in general G02B) · CPC title

• H01S2301/203

  with at least one hole in the intensity distribution, e.g. annular or doughnut mode · CPC title

• H01S2301/206

  Top hat profile · CPC title

• H01S3/10

  Controlling the intensity, frequency, phase, polarisation or direction of the emitted radiation, e.g. switching, gating, modulating or demodulating · CPC title

• H01S3/10061

  Polarization control · CPC title