The wchar_t* string is passed directly to Win32/CreateFileW
So, if you're able to use other Win32 file API calls, it should work for LibRaw too.
UPD: on modern windows, all interfaces are unicode already, starting from wmain/_tmain program 1st function, so there is no need to convert anything from/to 8-bit strings.
>> I tried various conversions
The wchar_t* string is passed directly to Win32/CreateFileW
So, if you're able to use other Win32 file API calls, it should work for LibRaw too.
UPD: on modern windows, all interfaces are unicode already, starting from wmain/_tmain program 1st function, so there is no need to convert anything from/to 8-bit strings.