Source: www.qldbridge.com 
Bergen raises became popular in the 80s and are now widely played. They let you make pre-emptive, mixed and limit raises efficiently, though they seem to commit your side to the three-level whenever you have four trumps facing a major-suit opener. (This is a mirage: you are at liberty to make a simple raise of 1 to 2 with: J 7 6 4 Q 10 3 J 9 2 K 8 6
Indeed, I would consider it an error in judgment not to do so.) Facing a pre-emptive raise, there are no game tries available. I suggest opener uses the four calls between partner’s call and game as slam-tries, codified according to the reverse Romex pattern: an unspecified shortsuit slam-try, and three long-suit slam tries, with 3NT showing spades in the heart auctions.
Opener might have: A K J 7 6 4 A J 3 2 A K 6
For his short-suit slam-try via 3NT-4-4. Responder can, as before, ask, sign-off without asking, or show concentrated values in return. After 1 – 3 – 3NT bid 4 on: 9 5 3 2 K Q 9 4 10 9 4 8 3
Opener can bid 6[ without further ado on the example hand above. Exactly the same logic applies after a limit jump-raise as after a pre-emptive raise, the only difference being the values that opener will require to make his slam-try.
After the Bergen sequences, opener has more room to explore. Before we look at his additional actions, let’s just mention in passing that while there are (at least in theory) two schools of thought as to whether the 3 or 3 response should be the limit, the other being the mixed, or 6-9 HCP raise, there is only one tenable position to hold here. The Mixed Raise is wide-ranging, since some would make the call over a 1 bid on:
7 6 Q 10 3 2 J 9 2 A Q 9 2
As well as on a club suit such as K 10 9 2. That being so, you need space to ask partner whether he was serious or joking with the Mixed Raise – hence 3 should be allocated to that call to give opener room to enquire with 3. By contrast, the range for a limit raise is very narrow. With a high-card range of 10-11, opener should not need space to ask more questions. (For the record: this general rule about making the limit raise the call directly below the trump suit holds in other common sequences such as ‘Unusual over Unusual’.)
So after our Mixed Raise we can sign-off in partscore or game, or use the first (cheapest) step as a range-ask (responder signs off, bids game, or cuebids with a maximum). In the sequence 1 – 3 – 3, the last call is a game try focusing on hearts. Opener’s actions above three of the major are Reverse Romex slam tries, as in our other sequences. (Step one for unspecified shortness, with three long-suit slam tries, and this includes 1– 3-3NT).