Transient Grating Spectrometer HARPIA-TG

  • Carrier diffusion coefficient in a matter of minutes!
  • Non-invasive measurement technique
  • Fully automated and computer controlled
  • Continuous setting of grating period
  • Sensitivity down to µJ/cm² excitation level
  • Advanced measurement and analysis software
  • Photoluminescence (PL) measurement option

Features

  • Carrier diffusion coefficient in a matter of minutes!
  • Non-invasive measurement technique
  • Fully automated and computer controlled
  • Continuous setting of grating period
  • Sensitivity down to µJ/cm² excitation level
  • Advanced measurement and analysis software
  • Photoluminescence (PL) measurement option

HARPIA-TG is a transient grating spectrometer for the measurement of carrier diffusion and lifetime. Measurements are based on the laser-induced transient grating (LITG) technique. This method enables simultaneous observation of non-equilibrium carrier recombination and diffusion by all‑optical means.

HARPIA-TG allows the characterization of electrically non‑conductive or non-fluorescent samples. It is suitable for semiconductors materials and derivatives, e.g., silicon carbide (SiC), gallium nitride (GaN), perovskites, organic and inorganic solar cells, quantum dots, and even complex nanostructures such as quantum wells.

Coupled with CARBIDE or PHAROS laser with integrated optical parametric amplifier (I-OPA), the compact system is fully automated and computer-controlled via advanced measurement and analysis software. Thus, the user only needs to put the sample in the holder and start the measurement to obtain the diffusion coefficient in a matter of minutes.

  • Carrier diffusion measurement
  • Carrier lifetime measurement
  • Carrier diffusion length measurement
  • Single-wavelength absorption

The principle of a LITG measurement is depicted in the figure on the right. A pair of ultrashort pulses are overlapped both spatially and temporally at the sample plane. Angular separation of the excitation beams causes them to interfere at their crossing. The period of the interference pattern Λ depends on the beam intersection angle and the pump wavelength.

Excitation by a periodic pattern creates a spatially-modulated excited carrier distribution and, effectively, a periodic modulation of the refractive index. Therefore, this pumping geometry produces a transient grating from which a temporally-delayed probe pulse can diffract. Over time, the laser-induced grating decays due to carrier recombination (electronic decay with the rate of τR) and carrier diffusion (spatial decay with the rate of τD ). The diffusion term depends on the transient grating period: fine gratings (small Λ values) diffuse faster than coarser ones (large Λ values).  Accordingly, if we measure the temporal behavior of the diffracted signal over a series of different periods Λ, we can determine the carrier diffusion coefficient D[cm2/s] from the relationship,

where τG is the net decay rate of the transient grating.

Parameter Value
Diffusion coefficient 0.1 – 50 cm2/s
Carrier lifetime 1 ps – 80 ns

I.

Transient decay dynamics are measured at various grating periods Λ. HARPIA-TG allows continuous tuning of the excitation grating period. Periods ranging from 1.15 to 15 μm (depending on the pump wavelength) can be formed at the sample plane.

II.

Data obtained at each grating period is fit to an exponential decay. The retrieved reciprocal decay constants are plotted
as a function of the inverse square of the grating period. Tangent of this curve provides the carrier diffusion coefficient (at the given carrier concentration and temperature), while the zero-intercept point (Λ = ∞ μm) provides the intrinsic carrier recombination rate τR.

III.

Experiment is repeated at various excitation intensities to obtain a comprehensive dependence of the diffusion coefficient on the non-equilibrium carrier concentration.

Polarization and pump wavelength control enables more advanced spin grating and thermal grating measurements, respectively.

Model HARPIA-TG
Grating recording wavelength 1) 340 – 560 nm
Probe wavelength 2) 1030 nm
Grating period 3) 1.15 – 15 μm
Pulse duration < 290 fs
Delay range Up to 8 ns
  1. Extendable to long-wave VIS/NIR. Contact sales@lightcon.com for details.
  2. SH (515 nm) or OPA-based probe is available upon request. Contact sales@lightcon.com for details.
  3. Depends on the excitation wavelength.
Model HARPIA-TG
Diffusion coefficient 0.1 – 50 cm2/s
Carrier lifetime 1 ps – 80 ns
Model HARPIA-TG
Physical dimensions (L × W × H)
730 × 420 × 188 mm

HARPIA-TG Transient Grating Spectrometer

Product datasheet.

Rev. 05/01/2024. Size 0.5 MB.

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