with the second one has a zero intensity?! So the first order of diffraction would be bright and the weak light from far stars could be analyzed
Theoretically yes. A sinusoidal phase grating (no absorption) where the amplitude of the phase shift is pi/2. This grating would only have 2 orders, +1 and -1.
If all you want is to get rid of the +/-2nd orders all you have to do is to make sure the line-to-space ratio of the grating is 1. This ratio gets rid of all the even diffraction orders. If you also make sure the grating is a perfect phase grating then you'll also get rid of the 0th order.
Read section 2.5.1 in my thesis (http://kth.diva-portal.org/smash/get/diva2:398800/FULLTEXT01.pdf), it's 1.5 pages and has the formula for the efficiency of gratings (absorption and phase) with a rectangular grating profile.
There are several options:
1. Using the high frequency grating and appropriate angles to have only two or even one orders.
2. Using the blazed grating to send almost all energy to the chosen order.
3. Using the selective multiple layer grating (look X-ray diffraction on a multilayer structure modulated by surface acoustic waves A. I. Erko, D. V. Roshchupkin, A. A. Snigirev, A. M. Smolovich, A. Yu. Nikulin, G. V. Vereshchagin. Nuclear Instruments and Methods in Physics Research Section A 1989; Vol. 282: pp. 634-637 https://www.researchgate.net/publication/234272572_X-ray_diffraction_on_a_multilayer_structure_modulated_by_surface_acoustic_waves).
Article X-ray diffraction on a multilayer structure modulated by sur...
Also in practice, you can even make an amplitude gratind with just sin^2 printed. I did it once by simply printing it on a transparent film and they were really just +/-1 and 0 order. But why do you need such a solution for star spectrometry? Normal gratings are just not enough?
You can practically design a binary phase grating with 0 and pi rad ridges, which will control the amplitude of n diffraction orders, the common design id called "Damman grating" you can for example design a gating with +1 and -1 orders which amplitude close to 1 and 2,3..N close to 0. the amount of suppression depend on manufacturing tolerances.
Now I can also recommend our recent publication https://www.researchgate.net/publication/318205293_Optical_elements_containing_semitransparent_wavelike_films?ev=prf_ov_fet_res&_iepl%5BviewId%5D=naUGL2OYHS3OMfbdaje0o4DlXt4IGN1eAXOo&_iepl%5Bcontexts%5D%5B0%5D=prfhpi&_iepl%5Bdata%5D%5BstandardItemCount%5D=4&_iepl%5Bdata%5D%5BuserSelectedItemCount%5D=0&_iepl%5Bdata%5D%5BtopHighlightCount%5D=2&_iepl%5Bdata%5D%5BstandardItemIndex%5D=1&_iepl%5Bdata%5D%5BstandardItem1of4%5D=1&_iepl%5BtargetEntityId%5D=PB%3A318205293&_iepl%5BinteractionType%5D=publicationTitle as addition to point 3 of my previous answer. In it the dynamic theory of light diffraction by a locally periodic multilayer semitransparent wavelike film is developed. A simple analytical formula for near Bragg diffraction order intensity is obtained for the case when only one diffraction order lies within the hologram angular selectivity. A numerical calculation of hologram diffraction efficiency was performed.
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