Laser repetition rate multiplier and flat-top beam profile generators using mirrors and/or prisms

Patent metadata

Field	Value
Publication number	US-10044164-B2
Application number	US-201615239268-A
Country	US
Kind code	B2
Filing date	Aug 17, 2016
Priority date	Jun 20, 2014
Publication date	Aug 7, 2018
Grant date	Aug 7, 2018

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

The invention claimed is:

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 said at least one 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,
wherein said two light reflective elements comprise a first curved mirror and a second curved mirror,
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;
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 cavity,
wherein the second beam splitter and the at least two fold mirrors are configured such that second portions of each said input pulse are transmitted along a secondary cavity loop inside the ring cavity, and
wherein the right-angled prism is configured to direct said first portions leaving the primary cavity loop to the secondary cavity loop.

10. The laser pulse repetition rate multiplier of claim 9 ,
wherein the first beam splitter is configured to direct said first portions of said each input laser pulse such that the first portions are reflected by the first and second curved mirrors in a first plane while on the primary cavity loop,
wherein the right-angle prism is configured to direct the first portions leaving the primary cavity loop to the second beam splitter, and
wherein the second beam splitter is configured to direct the second portions such that the second portions are 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.

Assignees

• Kla Tencor Corp

Inventors

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

Classifications

• H01S3/0071

  Beam steering, e.g. whereby a mirror outside the cavity is present to change the beam direction · CPC title

• H01S3/10046 Primary

  Pulse repetition rate control (H01S3/11 takes precedence) · CPC title

• H01S2301/20

  Lasers with a special output beam profile or cross-section, e.g. non-Gaussian · CPC title

• H01S2301/203

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

• H01S3/08004

  incorporating a dispersive element, e.g. a prism for wavelength selection (H01S3/0811, H01S3/08022 take precedence) · CPC title