System and Method for Isolating Gain Elements in a Laser System

Patent metadata

Field	Value
Publication number	US-2016165709-A1
Application number	US-201414562237-A
Country	US
Kind code	A1
Filing date	Dec 5, 2014
Priority date	Dec 5, 2014
Publication date	Jun 9, 2016
Grant date	—

Abstract

A method and apparatus for protecting the seed laser a laser produced plasma (LPP) extreme ultraviolet (EUV) light system are disclosed. An isolation stage positioned on an optical path diverts light reflected from further components in the LPP EUV light system from reaching the seed laser. The isolation stage comprises two AOMs that are separated by a delay line. The AOMs, when open, direct light onto the optical path and, when closed, direct light away from the optical path. The delay introduced by the delay line is determined so that the opening and the closing of the AOMs can be timed to direct a forward-moving pulse onto the optical path and to divert reflected light at other times. The isolation stage can be positioned between gain elements to prevent amplified reflected light from reaching the seed laser and other potentially harmful effects.

First claim

What is claimed is:

1 . A system comprising:
a laser seed module for producing laser light on an optical path; a first gain element positioned along the optical path; a second gain element positioned along the optical path after the first gain element; and an isolation stage positioned along the optical path between the first gain element and the second gain element, the isolation stage configured to divert light that has been reflected back along the optical path through the second gain element, the isolation stage comprising:
a first acoustic-optical modulator (AOM) configured to transition over a first period of time between a first state in which light is directed along the optical path and a second state in which light is not directed along the optical path;
a second AOM configured to transition over a second period of time between a first state in which light is directed along the optical path and a second state in which light is not directed along the optical path, the transition of the second AOM occurring at a time after the transition of the first AOM; and
a delay device positioned between the first AOM and the second AOM and configured to delay the transmission of light between the first AOM and the second AOM for a time determined based upon the first and second transition times of the AOMs such that any light reflected back along the optical path that passes through the second AOM will not pass through the first AOM and back to the laser seed module.

2 . The system of claim 1 , wherein the period of time to transition is further based upon a width of the laser beam.

3 . The system of claim 1 , wherein the delay is further based upon an occurrence of beam imaging.

4 . The system of claim 3 , wherein, if beam imaging occurs, the delay is further determined such that a first portion of the laser beam is diverted by the second AOM and a remaining portion of the laser beam is diverted by the first AOM.

5 . The system of claim 1 , further comprising one or more other elements positioned beyond the second gain element.

6 . The system of claim 5 , wherein the one or more other elements comprise an extreme ultraviolet (EUV) plasma chamber.

7 . The system of claim 5 , wherein the one or more other elements comprise a power amplifier.

8 . The system of claim 1 , wherein the first gain element and the second gain element comprise pre-amplifiers.

9 . The system of claim 1 , further comprising a second isolation stage positioned along the optical path beyond the second gain element.

10 . The system of claim 1 , further comprising a second isolation stage positioned along the optical path between the first gain element and the seed laser.

11 . The system of claim 1 , wherein the isolation stage is further configured to prevent self lasing in the first gain element by diverting reflected light.

12 . The system of claim 1 , wherein the first AOM and the second AOM are cross-fired.

13 . The system of claim 12 , wherein the delay is further determined based upon the width of the laser beam.

14 . A method comprising:
producing laser light on an optical path; passing a laser pulse generated from the laser light through a first gain element positioned along the optical path; passing the laser pulse through an isolation stage positioned along the optical path after the first gain element, the isolation stage configured to divert light reflected back along the optical path from any elements located beyond the isolation stage, the isolation stage comprising:
a first acoustic-optical modulator (AOM) configured to transition over a first period of time between a first state in which light is directed along the optical path and a second state in which light is not directed along the optical path;
a second AOM configured to transition over a second period of time between a first state in which light is directed along the optical path and a second state in which light is not directed along the optical path, the transition of the second AOM occurring at a time after the transition of the first AOM; and
a delay device positioned between the first AOM and the second AOM and configured to delay the transmission of light between the first AOM and the second AOM for a time determined based upon the first and second transition times of the AOMs such that any light reflected back along the optical path that passes through the second AOM will not pass through the first AOM and back to the laser seed module; and
passing the laser pulse through a second gain element positioned along the optical path after the isolation stage.

Assignees

• Asml Netherlands Bv

Inventors

• Tao Yezheng
• Brown Daniel John William
• Golich Daniel J
• Kats Michael
• Stewart John T
• Rokitski Rostislav

Classifications

• H05G2/0082 Primary

  the energy-carrying beam being a laser beam · CPC title

• H05G2/008 Primary

  involving an energy-carrying beam in the process of plasma generation · CPC title

• H05G2/003

  the plasma being generated from a material in a liquid or gas state · CPC title

• H01S3/2383

  Parallel arrangements · CPC title

• H01S3/2316

  Cascaded amplifiers · CPC title