Compact continuous wave tunable infrared lasers and method therefor

Abstract

A bulk, quasi-periodic phase-matched difference-frequency (DFG) process in field-poled LiNbO3 bulk crystal permits continuous tunability of the output radiation in the 3.0-4.1 mum wavelength range through grating rotation. DFG in QPM-LiNbO3 crystal, carried out using a Nd:YAG laser and a high power semiconductor laser at the quasi-phased matching (QPM) degeneracy point, results in an ultra wide 0.5 mum acceptance bandwidth, permitting crystal rotation-free wavelength tuning of 4.0-4.5 mum, with 0.2 mW output power at 4.5 mum.

What is claimed is:  
     
       1. A method for generating a laser beam having a desired wavelength from a first laser source having a first output which is adjustable in wavelength and a second laser source producing a second output of fixed wavelength in a system including a periodically poled non-linear bulk crystal receiving the first and second outputs at one face of the crystal, the method comprising the steps of: 
       adjusting the wavelength of the first output;  
       simultaneously rotating the bulk crystal by a selected angle; and  
       combining the first and second outputs to thereby generate a resultant output of the desired wavelength.  
     
     
       2. The method as recited in claim  1 , wherein the combining step comprises subtracting the first output from the second output to thereby generate the resultant output having a wavelength less than that of either the first or the second outputs. 
     
     
       3. The method as recited in claim  2 , wherein the adjusting and rotating steps are performed so as to satisfy the conditions: 
       (1) 1/λ 3 =1/λ 1 −1/λ 2 ; and  
       (2) Λ eff =n 3 /λ 3 −n 1 /λ 1 +n 2 /λ 2    
       where λ 3 , λ 1 , λ 2  are wavelengths of said resultant, said first and second outputs, respectively, Λ is the period of the gratings of the bulk crystal and n 3 , n 1 , and n 2  denote the index of refraction of the crystal for the wavelengths λ 3 , λ 1 , λ 2 , respectively. 
     
     
       4. The method as recited in claim  1 , wherein the combining step comprises summing the first output and the second output to thereby generate the resultant output having a wavelength greater than that of said first and said second outputs. 
     
     
       5. The method as recited in claim  4 , wherein the adjusting and rotating steps are performed so as to satisfy the conditions: 
       (1) 1/λ 3 =1/λ 1 +1/λ 2 ; and  
       (2) Λ eff =n 3 /λ 3 −[n 1 /λ 1 +n 2 λ 2 ] 
       where λ 3 , λ 1 , λ 2  are wavelengths of said resultant, said first and said second outputs, respectively, Λ is the period of the grating of the crystal and n 3 , n 1 , and n 2  denote the index of refraction of the bulk crystal for the wavelengths λ 3 , λ 1 ,  2 , respectively. 
     
     
       6. A combination generating a resultant laser beam of desired wavelength comprising: 
       a first laser device generating a first beam of adjustable wavelength;  
       a second laser device generating a second beam of fixed wavelength;  
       a periodically poled non-linear crystal receiving the first and second beams at one face of said crystal;  
       a rotating mechanism for rotating said crystal so as control the angle of incidence of said first and second beams with respect to said face of said crystal so as to permit said first and said second beams to combine and thereby form the resultant beam.  
     
     
       7. The combination as recited in claim  6 , wherein said rotating mechanism comprises a turntable. 
     
     
       8. A method for generating a laser beam having a desired wavelength range from a first laser source having a first output which is adjustable in wavelength and a second laser source producing a second output of fixed wavelength in a system including a periodically poled non-linear bulk crystal receiving the first and second outputs at one face of the crystal, the method comprising the steps of: 
       providing a periodically poled non-linear bulk crystal have a domain period substantially equal to but less than its respective degeneracy point;  
       selecting a fixed wavelength of said first output; and  
       combining said fixed output and the second output to thereby generate a resultant output in the desired wavelength range.  
     
     
       9. The method as recited in claim  8 , wherein the combining step comprises subtracting the first output from the second output to thereby generate the resultant output having a wavelength less than that of either the first or the second outputs. 
     
     
       10. A combination generating a resultant laser beam in a desired wavelength range, comprising: 
       a first laser device generating a first beam of adjustable wavelength;  
       a second laser device generating a second beam of fixed wavelength; and  
       a periodically poled non-linear crystal receiving the first and second beams at one face of said crystal, wherein the period of the crystal is substantially equal to but less than the degeneracy point for said crystal, said crystal combining said first and said second beams to thereby form the resultant beam in the desired frequency range.  
     
     
       11. A laser system generating a resultant laser beam in a desired wavelength range using difference-frequency generation (DFG) in a quasi-phase matched (QPM) LiNbO 3  crystal carried out using a Nd:YAG laser and a high power semiconductor laser, wherein said crystal is oriented at the (QPM) degeneracy point to thereby permit generation of a 0.5 μm acceptance bandwidth.