begin - create the initial field or diffractive wavefront.

Calling Sequence

[field_out]=begin(size,lambda[,number[,number2]])

Parameters

• size : the grid size of x axes and y axes in meters.
• lambda : the wavelength in meters.
• number : the grid dimension of x axes,now it must be even integer, number=256 if defaulted.
• number2 : the grid dimension of y axes, now it must be even integer, number2=number if defaulted.
• field_out : the output structure of field or diffractive wavefront, (in fact it is a 1xN matrix where N=30+2*number*number2)

Description

begin allocates memory for a square array of complex numbers, fills it with values corresponding to a uniform distribution of intensity and phase (plane wave) and construct a standard Scilab variant which include the header (containing information about sampling/wavelength/timstamp/frame,etc) and the formed field structure to use in the Scilab enviorment.

the amount of RAM needed : More than one megabyte is needed for 256x256 grid, 4MB for 512x512,16MB for 1024x1024 and a really large system is necessary for 2048x2048. These numbers may be slightly different for different computers. Some filters allocate additional memory (up to 8 times of the basic data structure in the worst case), rising further the memory requirements. If RAM is not sufficient, the system will swap to the hard-disk, slowing down not only your job, but the whole computer. The 512x512 size is safe for the majority of Unix systems.

Examples

	m=1;
	nm=1e-9*m;
	mm=1e-3*m;
	cm=1e-2*m;

	lambda=550*nm;
	sizes=5*mm;
	N1=32; N2=64;
	
	F1=begin(sizes,lambda);
	field_plot(F1);
	dwf_fits(F1,"file1");	
	
	F2=begin(sizes,lambda,N1);
	field_plot(F2);
	dwf_fits(F2,"file2");	
	
	F3=begin(sizes,lambda,N1,N2);
	field_plot(F3);
	dwf_fits(F3,"file3");	
 

Author

Chen jingyuan, Gan guangyong (IAPCM, China.)

See Also

create_field ,   interpol ,   sp_wave ,   pl_wave ,   start ,   emitter ,