EXHIBIT 31.1

Rule 13a-14(a)/15d-14(a) Certification of the
Chief Executive Officer

I, Günther
Braun, Chief Executive Officer of Rofin-Sinar Technologies, Inc., certify that:

|   |                                                                                                                                                                                                                                                                                                                                                  |                                                                                                                                                                                                                                                                                                                                                                                                  
|-- | ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------ | -------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
|1. | I have
  reviewed this Annual Report on Form 10-K of Rofin-Sinar Technologies Inc.                                                                                                                                                                                                                                                              
|   |                                                                                                                                                                                                                                                                                                                                                 
|2. | Based on my
  knowledge, this Annual Report does not contain any untrue statement of a
  material fact or omit to state a material fact necessary to make the
  statements made, in light of the circumstances under which such statements
  were made, not misleading with respect to the period covered by this report.                       
|   |                                                                                                                                                                                                                                                                                                                                                 
|3. | Based on my
  knowledge, the financial statements, and other financial information included
  in this Annual Report, fairly present in all material respects the financial
  condition, results of operations and cash flows of the Registrant as of, and
  for, the periods presented in this Annual Report.                                   
|   |                                                                                                                                                                                                                                                                                                                                                 
|4. | The
  Registrants other certifying officer(s) and I are responsible for
  establishing and maintaining disclosure controls and procedures (as defined
  in Exchange Act Rules 13a-15(e) and 15d-15(e)) and internal control over
  financial reporting (as defined in Exchange Act Rules 13a-15(f) and 15d-15(f)
  for the Registrant and have:
|   |                                                                                                                                                                                                                                                                                                                                                 
|   | a)                                                                                                                                                                                                                                                                                                                                               | designed
  such disclosure controls and procedures, or caused such disclosure controls
  and procedures to be designed under our supervision, to ensure that material
  information relating to the Registrant, including its consolidated
  subsidiaries, is made known to us by others within those entities,
  particularly during the period in which this report is being prepared;         
|   |                                                                                                                                                                                                                                                                                                                                                  |                                                                                                                                                                                                                                                                                                                                                                                                  
|   | b)                                                                                                                                                                                                                                                                                                                                               | designed such
  internal control over financial reporting, or caused such internal control
  over financial reporting to be designed under our supervision, to provide
  reasonable assurance regarding the reliability of financial reporting and the
  preparation of financial statements for external purposes in accordance with
  generally accepted accounting principles;                
|   |                                                                                                                                                                                                                                                                                                                                                  |                                                                                                                                                                                                                                                                                                                                                                                                  
|   | c)                                                                                                                                                                                                                                                                                                                                               | evaluated
  the effectiveness of the Registrants disclosure controls and procedures
  presented in this report our conclusions about the effectiveness of the
  disclosure controls and procedures, as of the end of the period covered by
  this report, based on such evaluation; and                                                                                                         
|   |                                                                                                                                                                                                                                                                                                                                                  |                                                                                                                                                                                                                                                                                                                                                                                                  
|   | d)                                                                                                                                                                                                                                                                                                                                               | disclosed in
  this report any change in the Registrants internal control over financial
  reporting that occurred during the registrants most recent fiscal quarter
  (the Registrants fourth fiscal quarter in the case of an Annual Report) that
  has materially affected, or is reasonably likely to materially affect, the
  registrants internal control over financial reporting; and
|   |                                                                                                                                                                                                                                                                                                                                                  |                                                                                                                                                                                                                                                                                                                                                                                                  
|5. | The
  Registrants other certifying officer and I have disclosed, based on our most
  recent evaluation of internal control over financial reporting, to the
  Registrants auditors and the audit committee of Registrants board of
  directors (or persons performing the equivalent functions):                                             
|   |                                                                                                                                                                                                                                                                                                                                                 
|   | a)                                                                                                                                                                                                                                                                                                                                               | all
  significant deficiencies and material weaknesses in the design or operation
  of internal control over financial reporting which are reasonably likely to
  adversely affect the Registrants ability to record, process, summarize and
  report financial information; and                                                                                                                
|   |                                                                                                                                                                                                                                                                                                                                                  |                                                                                                                                                                                                                                                                                                                                                                                                  
|   | b)                                                                                                                                                                                                                                                                                                                                               | any fraud,
  whether or not material, that involves management or other employees who have
  a significant role in the Registrants internal control over financial
  reporting.                                                                                                                                                                                                                 

Date: December
12, 2006

| |                           | 
| | ------------------------- | 
| | /s/ Günther
  Braun       | 
| |                           | 
| | Günther
  Braun           | 
| | Chief
  Executive Officer | 

---