Laser apparatus and extreme ultraviolet light generation apparatus

Abstract

A laser apparatus may include a master oscillator configured to output a pulse laser beam, an amplifier disposed in a light path of the pulse laser beam, a wavelength selection element disposed in the light path of the pulse laser beam and configured to transmit light of a selection wavelength at higher transmittance than transmittance of light of other wavelengths, and a controller configured to change the selection wavelength of the wavelength selection element.

What is claimed is: 
     
       1. A laser apparatus comprising:
 a master oscillator configured to output a pulse laser beam; 
 an amplifier disposed in a light path of the pulse laser beam; 
 a wavelength selection element disposed in the light path of the pulse laser beam and configured to be switched between (1) a first state and (2) a second state to suppress spontaneous emission light from being amplified and entering the master oscillator, to suppress spontaneous emission light from being amplified and striking the target, or to suppress reflection light of the pulse laser beam reflected by the target from being amplified and entering the master oscillator,
 (1) the wavelength selection element in the first state having (1-1) a first transmittance for light of a first wavelength and (1-2) a second transmittance for light of a second wavelength, the second transmittance being lower than the first transmittance, 
 (2) the wavelength selection element in the second state having (2-1) a third transmittance for light of the first wavelength for which the amplifier has a first amplification factor, the third transmittance being lower than the first transmittance, and (2-2) a fourth transmittance for light of the second wavelength for which the amplifier has a second amplification factor lower than the first amplification factor, the fourth transmittance being higher than the third transmittance; and 
 
 a controller configured to switch the wavelength selection element. 
 
     
     
       2. The laser apparatus according to  claim 1 , wherein the wavelength selection element is disposed in the light path of the pulse laser beam output from the master oscillator. 
     
     
       3. The laser apparatus according to  claim 1 , wherein the wavelength selection element includes an etalon that is provided with a first substrate on one surface of which a first partially reflective film is formed, a second substrate which is disposed opposing the first substrate and on a surface of which a second partially reflective film is formed while the surface opposing the first partially reflective film, and a piezoelectric element configured to increase/decrease a distance between the first substrate and the second substrate. 
     
     
       4. The laser apparatus according to  claim 1 , wherein the amplifier has a third amplification factor for light of a third wavelength different from the first wavelength the third amplification factor being higher than the second amplification factor, the third wavelength being included within a free spectral range of the wavelength selection element in the first state and also within a free spectral range of the wavelength selection element in the second state. 
     
     
       5. The laser apparatus according to  claim 1 , wherein
 the master oscillator is configured to output the pulse laser beam including multiple pulses, and 
 the controller is configured to switch the wavelength selection element to the second state after each of the multiple pulses output from the master oscillator passes through the wavelength selection element and to switch the wavelength selection element to the first state before next pulse of each of the multiple pulses output from the master oscillator reaches the wavelength selection element. 
 
     
     
       6. The laser apparatus according to  claim 1 , wherein
 the master oscillator is configured to output the pulse laser beam including multiple pulses, and 
 the controller is configured to switch the wavelength selection element so that the wavelength selection element is in the first state in a first period during which the master oscillator repeatedly outputs the multiple pulses whereas the wavelength selection element is in the second state in a second period during which the master oscillator stops the repeated output of the multiple pulses. 
 
     
     
       7. The laser apparatus according to  claim 1 , further comprising:
 a light source configured to emit light of the second wavelength toward the wavelength selection element; and 
 a light sensor disposed in a light path of the light that is emitted from the light source and passes through the wavelength selection element, 
 wherein the controller is configured to switch the wavelength selection element in accordance with output of the light sensor. 
 
     
     
       8. An extreme ultraviolet light generation apparatus comprising:
 a laser apparatus that includes
 a master oscillator configured to output a pulse laser beam, 
 an amplifier disposed in a light path of the pulse laser beam, 
 a wavelength selection element disposed in the light path of the pulse laser beam and configured to be switched between (1) a first state and (2) a second state to suppress spontaneous emission light from being amplified and entering the master oscillator, to suppress spontaneous emission light from being amplified and striking the target, or to suppress reflection light of the pulse laser beam reflected by the target from being amplified and entering the master oscillator, 
 (1) the wavelength selection element in the first state having (1-1) a first transmittance for light of a first wavelength and (1-2) a second transmittance for light of a second wavelength, the second transmittance being lower than the first transmittance, 
 (2) the wavelength selection element in the second state having (2-1) a third transmittance for light of the first wavelength for which the amplifier has a first amplification factor, the third transmittance being lower than the first transmittance, and (2-2) a fourth transmittance for light of the second wavelength for which the amplifier has a second amplification factor lower than the first amplification factor, the fourth transmittance being higher than the third transmittance, and 
 a controller configured to switch the wavelength selection element; 
 
 a chamber provided with an incidence opening through which a pulse laser beam outputted from the laser apparatus passes into the inside of the chamber; 
 a target supply device configured to output a target into the chamber; and 
 a laser beam focusing optical system configured to focus the pulse laser beam inside the chamber. 
 
     
     
       9. The extreme ultraviolet light generation apparatus according to  claim 8 , wherein the wavelength selection element is disposed in the light path of the pulse laser beam output from the master oscillator. 
     
     
       10. The extreme ultraviolet light generation apparatus according to  claim 8 , wherein the amplifier has a third amplification factor for light of a third wavelength different from the first wavelength, the third amplification factor being higher than the second amplification factor, the third wavelength being included within a free spectral range of the wavelength selection element in the first state and also within a free spectral range of the wavelength selection element in the second state. 
     
     
       11. The extreme ultraviolet light generation apparatus according to  claim 8 , wherein
 the master oscillator is configured to output the pulse laser beam including multiple pulses, and 
 the controller is configured to switch the wavelength selection element to the second state after each of the multiple pulses output from the master oscillator passes through the wavelength selection element and to switch the wavelength selection element to the first state before next pulse of each of the multiple pulses output from the master oscillator reaches the wavelength selection element. 
 
     
     
       12. The extreme ultraviolet light generation apparatus according to  claim 8 , wherein
 the master oscillator is configured to output the pulse laser beam including multiple pulses, and 
 the controller is configured to switch the wavelength selection element so that the wavelength selection element is in the first state in a first period during which the master oscillator repeatedly outputs the multiple pulses whereas the wavelength selection element is in the second state in a second period during which the master oscillator stops the repeated output of the multiple pulses.