Ultrafast laser inscription (ULI) is a rapidly maturing technique which uses focused ultrashort laser pulses to locally
modify the refractive index of dielectric materials in three-dimensions (3D). Recently, ULI has been applied to the
fabrication of astrophotonic devices such as integrated beam combiners, 3D integrated waveguide fan-outs and
multimode-to-single mode convertors (photonic lanterns). Here, we outline our work on applying ULI to the fabrication
of volume phase gratings (VPGs) in fused silica and gallium lanthanum sulphide (GLS) glasses. The VPGs we fabricated
had a spatial frequency of 333 lines/mm. The optimum fused silica grating was found to exhibit a first order diffraction
efficiency of 40 % at 633 nm, but exhibited approximately 40 % integrated scattered light. The optimum GLS grating
was found to exhibit a first order diffraction efficiency of 71 % at 633 nm and less than 5 % integrated scattered light.
Importantly for future astronomy applications, both gratings survived cooling to 20 K. This paper summarises the grating
design and ULI manufacturing process, and provides details of the diffraction efficiency performance and blaze curves
for the VPGs. In contrast to conventional fabrication technologies, ULI can be used to fabricate VPGs in almost any
dielectric material, including mid-IR transmitting materials such as the GLS glass used here. Furthermore, ULI
potentially provides the freedom to produce complex groove patterns or blazed gratings. For these reasons, we believe
that ULI opens the way towards the development of novel VPGs for future astronomy related applications.