Diffractive Homogenizer for Diode Laser Uniformity
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Solution Overview
Problem
Diode laser pump arrays in high average power diode pumped solid state lasers produce anisotropic illumination due to uneven beam divergence, leading to non-uniform intensity profiles and reduced efficiency in solid state amplifiers and lasers.
Innovation Solution
A diffractive homogenizer system using photo-thermo-refractive glass is integrated along the optical path of the diode laser array, with a method of fabricating diffractive homogenizers involving UV exposure and thermal treatment to create a continuously varying index of refraction profile, ensuring uniform intensity profiles and improved beam quality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If lenslet arrays are used to match divergence angles, then the vertical divergence angle is reduced to match the horizontal divergence angle, but the intensity profile remains non-uniform with variations greater than 10%
Solution Approach 1:
The patent changes the optical parameters of the glass member by exposing it to UV radiation through a mask with varying transmissivity, creating spatially varying refractive index or absorption coefficients. This modifies the light propagation characteristics to achieve uniform intensity distribution without adding complex optical components.
Solution Approach 2:
The glass member acts as an intermediary element between the diode laser array and the amplifier slab. By preprocessing the light field through this intermediate medium with spatially varying properties, the non-uniform intensity profile is corrected before the light reaches the amplifier.
2Manufacturing precision
If a diffractive homogenizer with continuously varying index of refraction is used, then intensity variation is reduced to less than 10%, but the fabrication process becomes more complex requiring UV exposure and thermal treatment
Solution Approach 1:
The patent replaces traditional mechanical fabrication methods (such as precision machining or lithographic etching) with a photochemical approach. UV radiation exposure through a mask creates the desired refractive index or absorption profile through photo-induced changes in the glass material, followed by thermal treatment to stabilize the structure.
Solution Approach 2:
The fabrication process exploits parameter changes in the glass material induced by UV exposure and thermal treatment. The material's refractive index or absorption coefficient is spatially modulated during exposure and then stabilized through thermal processing, achieving precise intensity control without complex mechanical fabrication.
3Power
If diode laser pump arrays are used to pump large aperture amplifiers, then high average power is achieved, but anisotropic illumination with intensity variation greater than 10% reduces extraction efficiency
Solution Approach 1:
The patent applies local quality modification by creating spatially varying refractive index or absorption coefficients in the glass member. Different regions of the glass member have different optical properties that compensate for the anisotropic illumination pattern from the diode laser array, ensuring uniform energy deposition in the amplifier.
Solution Approach 2:
The optical parameters of the glass member are changed through UV exposure and thermal treatment to create a spatial map of refractive index or absorption coefficients that matches the inverse of the diode array's intensity distribution, thereby achieving uniform illumination and maximizing extraction efficiency.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution achieves a uniform intensity profile with intensity variation less than 10%, enhancing extraction efficiency, beam quality, and reducing thermally induced wavefront distortions, with transfer efficiencies exceeding 98% and improved reliability of the laser device.
Implementation Method 1
directing UV radiation through the partially transmissive optical element to impinge on the PTR glass
Implementation Method 2
exposing a predetermined portion of the PTR glass to the UV radiation to create a diffractive homogenizer with a predetermined index of refraction profile
Implementation Method 3
thermally treating the PTR glass to create a continuously varying index of refraction profile as a function of position within the transparent optical element
Implementation Method 4
The diffractive optic includes a photo-thermo-refractive glass member... A second intensity profile measured at the input face of the amplifier slab has a variation less than 10%
Data Source
Figure 1~2
Figure 3
Figure 4
AI summary
A method of fabricating a diffractive homogenizer comprises: providing a partially transmissive optical element having a predetermined grayscale intensity pattern thereon (610); providing a transparent optical element (612); directing UV radiation through the partially transmissive optical element to impinge on the transparent optical element (614); exposing a predetermined portion of the transparent optical element to the UV radiation (616); and thermally treating the transparent optical element to produce the diffractive homogenizer (618) characterized by a continuously varying index of refraction profile as a function of position within the transparent optical element.