PowerShell and DateTime

I create a type:

          $authTicketRepresentationSource = @"
using System;

namespace SonicFoundry.Mediasite.WebApi.Model
{
    public class AuthorizationTicketRepresentation`
    {`
        public string TicketId { get; set; }
        public string Username { get; set; }
        public string ClientIpAddress { get; set; }
        public string Owner { get; set; }
        public DateTime CreationTime { get; set; }
        public DateTime ExpirationTime { get; set; }
        public string ResourceId { get; set; }
        public int MinutesToLive { get; set; }
    }
}
"@
          Add-Type -TypeDefinition $authTicketRepresentationSource

I create an instance and populate it ad convert it to a JSON string:

        $PostStr = [System.Text.Encoding]::UTF8.GetBytes($jsonAuthTicketRepresentation.ToString())

Then I POST this data to a URL. The problem is that the dates come out as:

{
    "TicketId":  "00000000-0000-0000-0000-000000000000",
    "Username":  "kevinb",
    "ClientIpAddress":  "10.0.70.154",
    "Owner":  "",
    "CreationTime":  "\/Date(1379610208888)\/",
    "ExpirationTime":  "\/Date(-62135575200000)\/",
    "ResourceId":  "773820afc2004c8dad7b8c023201dec218",
    "MinutesToLive":  5
}

Rather than

{"TicketId":"00000000-0000-0000-0000-000000000000","Username":"kevinb","ClientIpAddress":"10.0.70.154","Owner":"","CreationTime":"2013-09-19T12:34:22.0987775-05:00","ExpirationTime":"0001-01-01T00:00:00","ResourceId":"599bc68366fd407a81c004e9ca91147a1d","MinutesToLive":5
}

This is causing deserialization issues with the server that this data is being posted to. How can I get the latter serialized representation of dates?

Thank you.

---

Kevin Burton