PovRay rendering stops when simulating Gaussian beam passing through lens

Question

I am trying to create a scene in PovRay where I have a Gaussian beam (tilted by 45°) passing through a lens with a focal point of 500mm, then reflecting off a flat surface. Rendering without the lens is no problem but at the point when I included the lens, the rendering no longer finishes.

When reducing the photon count to 100K, the scene can be rendered but the quality is not good. When I use photon spacing instead, it doesn't finish the render at any given value. I have tried rendering on Windows and Linux. In the render message, the first photon count is always a different value but after that, every photon count is 0. It then looks like this:

==== [Rendering...] ========================================================
Photon count 608402
Photon count 0
Photon count 0
Photon count 0
Photon count 0
Photon count 0
Photon count 0
     ...

Here is my code, I currently have:

    // adding a photon{} block to global_settings activates photon mapping.
    // photons also need to be adjusted for light sources and objects.
    global_settings {
        photons {
            //spacing 0.01                              // specify the density of photons (0.001) for quite good quality  
            count 100000                                // alternatively use a total number of photons
            
            //gather min, max                           // amount of photons gathered during render [20, 100]
            media 20                                    // media photons
            jitter 1                                    // jitter phor photon rays
            max_trace_level 5                           // optional separate max_trace_level
            adc_bailout 1/255                           // see global adc_bailout
            //save_file "filename"                      // save photons to file
            //load_file "filename"                      // load photons from file
            autostop 0                                  // photon autostop option
            radius 10                                   // manually specified search radius
            //steps 20
            expand_thresholds 0.2, 40
        }
    } 
#declare surface_radius = 200;                          // radius of surface
#declare incident_angle = 45;                           // angle for lightreflection
#declare beam_intensity = 10000;                        // intensity of beam 
#declare lense_distance = 524; 
#declare radius_lense = 400;               

#declare lense =        intersection{
                            sphere{ <0,0,0>, radius_lense scale<1,1,1>  rotate<0,0,0>  translate<0,radius_lense-0.01,0>  
                            }                             
                            sphere{ <0,0,0>, radius_lense scale<1,1,1>  rotate<0,0,0>  translate<0,-radius_lense+0.01,0>  
                        }
                            material{   
                                texture { pigment{ rgbf <0.98, 0.98, 0.98, 0.9> }
                                          finish { diffuse 0.1 reflection 0.2 specular 0.8 roughness 0.0003 phong 1 phong_size 400}
                                } 
                                interior{ ior 1.5 caustics 0
                                } 
                            } 
                             
                            translate<0,lense_distance,0> rotate<0,0,incident_angle>
                            photons {
                                target
                                refraction on
                                reflection off
                                collect off
                            }  
                        }

camera {
    location <-40,40,-70>                             // position
    look_at  <0, 0, 0>                                // view
    right x*1920/1080                                 // aspect
    angle 40
}

// Gaussian
light_source {
    <0,0,0>                                           // light's position (translated below)
    color rgb <0,beam_intensity,0>                    // light's color and intensity
    //spotlight
    cylinder
    translate <0,2*lense_distance, 0>                             // <x y z> position of light 
    parallel
    point_at <0, 0, 0>                                // direction of spotlight
    radius 5                                          // hotspot (inner, in degrees)
    tightness 5                                       // tightness of falloff (1...100) lower is softer, higher is tighter
    falloff 5                                         // intensity falloff radius (outer, in degrees) 
    rotate <0,0,incident_angle>
}

object{lense} 

// flat surface
union{
    merge{       
        cylinder { <0,-1,0>,<0,0,0>, surface_radius} 
        
    }
    texture{ pigment { color rgb<1,1,1> }
        normal { spotted 0.1 scale -0.005 }
        finish { specular 1 phong 1 reflection{ 1.00 metallic 1.00} }
    } 
    scale <1,1,1> rotate <0,0,0> translate<0,0,0>
    photons {
        target
        refraction off
        reflection on
        collect on
    }
}