Laser Pulse Compression & Stretching
Highly effective compression and stretching of picosecond and femtosecond laser pulses can be accomplished by using matched pairs of Volume Phase Holographic Gratings (VPHGs) in transmission geometry. As shown in the figure below, compression and stretching is proportional to the distance between the parallel gratings. A mirror can be inserted to double the dispersion and/or two identical lenses can be placed two focal lengths apart for compression purposes.

Benefits

Diffraction efficiencies >90%, combined with angles up to 70 degrees for S (TE) polarization, produce high throughput, compact devices.

Example Graph Below of 1213 lpmm grating (70.1 degrees) for 1550nm

 

 

 

 

 

 

 

 

 

Energy Density Information

We are collecting energy density data from various pulsed laser companies. Energy density failure is a mostly a function of the glue/gelatin/glass assembly with the glue usually failing first by softening. Below is information typical of a successful medical pulsed laser application. Continuous wave (CW) energy densities of up to ~10 watts/cm^2 are fine; up to ~100 10 watts/cm^2 is possible with suitable epoxies.

Energy Density Measurements (approximate) from Customers 

  • 2 Piece Glass Construction: Grating Diagrams
  • BK7 (2mm substrate + 2mm cover glass) and water white (1mm substrate + 1mm cover glass
  • NOA 61 or NOA 63 Epoxy: thickness ~25-50 microns
  • DCG Films: thicknesses vary from ~3-10 microns
Description Application #1 Application #2 Application #3
Pulsed Laser Type 1054nm, S polarized  

800nm, P polarized

530nm, P polarized
Grating Size >25mm >10mm >10mm
Beam Diameter  

5mm

3mm  

1.5mm

Pulse Duration 500 fs 130 fs <200 fs
Energy/pulse 30 microjoules  

360 microjoules

7 microjoules
Repetition Rate >10 KHz 1 KHz 1 KHz
Average Power 

(Energy/pulse X Repetition Rate )

>300 mW >300 mW >7 mW
Average Power Density 

(Average Power / Beam Area)

>1.5 Watts/cm2 >5 Watts/cm2 0.5 Watts/cm2
Peak Power 

((Energy/pulse) / Pulse Duration)

6×10^7 Watts 3×10^9 Watts >3×10^7 Watts
Peak Power Density 

(Peak Power / Beam Area)

3×10^8 Watts/cm2 4×10^10 Watts/cm2 2×10^9 Watts/cm2
Test Duration In commercial use 1.5 hours with no failure Preliminary

External Cavity Laser Tuning

Description
External cavity diode and dye lasers can be spectrally tuned and made to operate in a single-mode. Light exiting from the laser cavity diverges, passes through a collimator, and is imaged on a grating. In Littrow and Littman configurations, the grating is positioned so that light of the correct wavelength is redirected back through the collimator and focused into the laser cavity. Gratings for single or dual polarizations can be produced.

 

 

 

 

Littman System Using VPH Transmission Gratings, S (TE) Maximized

Grating Enhanced External Cavity Laser Diode (GEECLD): Graphs & diagrams courtesy of Andreas Wicht, University of Dusseldorf


 

Benefits

  • Tunable Diffraction Efficiency (>90%): High diffraction efficiencies are helpful to detune the laser far away from gain maximum.  Alternatively, to circumvent the gain maximum, especially at high currents, lower diffraction efficiencies are preferred.
  • Higher Spatial Frequencies (=> More Compact): In all Littman diode setups, transmission gratings allow the application of line densities which are about twice as large as for reflection gratings. This is because the first order is diffracted back into the laser diode, and not at ~90 degrees with respect to the incident beam.
  • Maximum Diffraction Efficiency: Higher efficiency than commercial reflection gratings.
  • Continuous Tuning Over A Wide Band

Stock: Dual Polarization VPH Transmission Gratings: AOI=AOD

Stock: Dual Polarization VPH Transmission Gratings: AOI=AOD
Description Spatial Frequency

Center Wavelength

AOI/AODat CWL S & P Efficiencies
Dickson®Grating 940 lpmm 1550nm 46.8o >90%
Dickson®Grating 1145 lpmm 1310nm 48.6o >90%
Custom VPH Transmission Gratings: >90% Efficiencies  

  • Polarizations Maximized: Single or dual polarization gratings (including Dickson® Gratings)
  • Symmetric or Non-Symmetric: Angle of Incidence (AOI) = Angle of Diffraction (AOD) or AOI ¹AOD
  • Frequencies: 400-4000 l/mm  ·  WavelengthRanges:350nm-2500nm   ·  Sizes: <5mm to >100mm
  • Environmentally Rugged ·  Substrates: BK7, Fused Silica               ·   Wavefront: <1/4 wave available
  • Energy Density: Continuous Wave is 100 watts/cm2 with appropriate epoxy selection.

 

 

 

 

 

 

 

 

 

 

These VPHGs can be customized for almost any wavelength or spatial frequency, are environmentally rugged, and scratch resistant. Process Instruments uses of our volume phase holographic gratings for their diode laser systems.

We provide a high level of customer service. Additionally, we offer consulting, design, prototype, product integration, and quantity production at competitive prices. For sales info contact 435-752-4301, email us, or send us a completed Customer Grating Worksheet.