Apparatus for spectrally combining broadband laser beams by volume bragg gratings

Abstract

A spectral beam combiner includes at least one transmitting volume chirped Bragg grating (TVCBG) which 1. diffracts a first broadband beam propagating at one central wavelength, which satisfies the Bragg condition, and incident on the TVCBG at one of (+) (−) Bragg angles, and 2. transmits at least one second broadband beam propagating at a second central wavelength, which does not satisfy the Bragg condition. The second broadband beam is incident on the TVCBG at the Bragg angle which is opposite to the one Bragg angle of the first broadband beam. The TVCBG is configured to eliminate divergence of the first broadband beam, which is resulted from dispersion of the one TVCBG, in a plane of diffraction, and combine the first diffracted and second transmitted broadband beams into a first single high-power collimated broadband output beam.

What is claimed is: 
     
         1 . A spectral beam combiner comprising at least one transmitting volume chirped Bragg grating (TVCBG) which
 diffracts a first broadband beam propagating at one central wavelength, which satisfies the Bragg condition, and incident on the TVCBG at one of (+)(−) Bragg angles, and   transmits at least one second broadband beam propagating at a second central wavelength, which does not satisfy the Bragg condition, and incident on the TVCBG at the Bragg angle which is opposite to the one Bragg angle of the first broadband beam,   
       wherein the one TVCBG is configured to:
 eliminate divergence of the first broadband beam, which is resulted from dispersion of the one TVCBG, in a plane of diffraction, and 
 combine the first diffracted and second transmitted broadband beams into a first single high-power collimated broadband output beam. 
 
     
     
         2 . The spectral beam combiner of  claim 1  further comprising at least one or more additional TVCBGs located upstream or downstream from the one TVCBG and diffracting a third broadband beam propagating at the Bragg angle and incident on the additional TVCBG at a central wavelength which satisfies the Bragg condition, wherein the additional TVCBG merges the first collimated output additional beams into a second high-power collimated broadband output beam. 
     
     
         3 . The spectral beam combiner of  claim 1  further comprising a first thermal lens compensator, wherein a thermal lens is induced in the one TVCBG by one of or both first and second broadband beams. 
     
     
         4 . The spectral beam combiner of  claim 3 , wherein the first thermal lens compensator includes a holographic achromatic broadband phase mask (HAPM) recorded in a designated PTR glass plate which is located downstream from the one TVCBG or recorded in a PTR glass plate with the one TVBG. 
     
     
         5 . The spectral beam combiner of  claim 3 , wherein the first thermal lens compensator includes a pair of holographic phase masks (HPM) which are aligned at respective opposite Bragg angles upstream from the one TVCBG, the HPMs diffracting the second broadband beam while converting a Gaussian intensity profile thereof to a donut-shaped intensity profile. 
     
     
         6 . The spectral beam combiner of  claim 1  further comprising at least one pair of identical first and second transmitting volume Bragg gratings (TVBGs) in optical communication with the TVCBG and spaced therefrom along a light path, the TVBGs being spaced apart and aligned at respective opposite “+” and “−” Bragg angles. 
     
     
         7 . The spectral beam combiner of  claim 6 , wherein the first and second TVBG sequentially diffract a fourth broadband beam at a fourth central wavelength satisfying the Bragg condition to provide a twice-diffracted fourth collimated broadband beam, the second TVBG transmitting the first broadband output beam which merges with the twice-diffracted fourth collimated beam into a single third broadband collimated output beam. 
     
     
         8 . The spectral beam combiner of  claim 7  further comprising at least one additional pair of first and second identical TVBGs aligned at respective opposite Bragg angles to provide sequential diffraction of a fifth broadband beam at a fifth central wavelength which satisfies the Bragg condition and is different from the first, second and fourth central wavelengths. 
     
     
         9 . The spectral beam combiner of  claim 8 , wherein the first and second TVBGs of respective pairs each are recorded in a designated PTR glass plates. 
     
     
         10 . The spectral beam combiner of  claim 8 , wherein the first TVBGs of respective pairs each are recorded in a designated PTR glass plate, whereas the second TVBGs of respective pairs both are recorded in a single multiplexing PTR glass plate. 
     
     
         11 . The spectral beam combiner of  claim 6  further comprising a second thermal lens compensator including a holographic achromatic broadband phase mask (HAPM) recorded in a designated F glass plate which is located downstream from the second TVBG or recorded in the PR glass with the second TVBG. 
     
     
         12 . The spectral beam combiner of  claim 6  further comprising a second thermal lens compensator which includes a pair of holographic phase masks (HPM) and is located upstream from the first TVBG, the HPMs being aligned at respective opposite Bragg angles so as to twice diffract the first broadband collimated output beam second broadband beam while converting a Gaussian intensity profile thereof to a donut-shaped intensity profile. 
     
     
         13 . The spectral beam combiner of  claim 12 , wherein the first broadband collimated output beam with the donut-shaped intensity profile merges with the fourth twice-diffracted broadband beam in the second TVBG such that the third collimated broadband output beam has a flattop intensity profile. 
     
     
         14 . The spectral beam combiner of  claim 6 , wherein the first and second TVBGs each have a thickness of at most about 1 mm and refractive index modulation (RIM) of about 1000 ppm to provide a 100% diffraction efficiency at a wavelength of the twice-diffracted first broadband beam in a 1 μm range. 
     
     
         15 . The spectral beam combiner of  claim 6 , wherein the first and second TVBGs are apodized to minimize leakage between diffracted and transmitted beams, the apodized TVBGs being configured with a bell-shaped profile of RIM recorded in a direction perpendicular to a grating vector of the TVBG. 
     
     
         16 . The spectral beam combiner of  claim 1 , wherein the first and second broadband beams each have a spectral width ranging between 3 and 10 nm. 
     
     
         17 . The spectral beam combiner of  claim 1 , wherein the first and second broadband beams each are a single transverse mode beam or multimode beam. 
     
     
         18 . The spectral beam combiner of  claim 6 , wherein the first and second TVBGs each are configured with a grating vector (K G ) which has an arbitrary orientation relative to the surface. 
     
     
         19 . The spectral beam combiner of  claim 1 , wherein the first and second central wavelengths each are selected from a 205-3500 nm wavelength range.